Technical Glossary



A measure or set of measures designed to permanently eliminate a hazard (e.g., lead-based paint). Abatement strategies include removal of the hazardous materials, replacement of building components containing the hazardous material, enclosure, or encapsulation. All of these strategies require proper preparation, cleanup, waste disposal, post-abatement clearance testing, and if applicable, record keeping and monitoring. Abatement activities are not allowable expenses to be funded by Department of Energy Weatherization Assistance Program dollars.
Absolute Humidity
Air moisture content expressed in grains (or pounds) of water vapor per pound of dry air.
The ratio of a solar energy absorbed to incident solar. Also called absorbtivity.
A solid material’s ability to draw in and hold liquid or gas.
Accent Lighting
Accent lighting illuminates walls, reduces brightness and contrast between walls and ceilings or windows.
Adhesion of a thin layer of molecules to a surface they contact.
Air Barrier
Any part of the building shell that offers resistance to air leakage. The air barrier is effective if it stops most air leakage. The primary air barrier is the most effective of a series of air barriers.
Air Changes per Hour at 50 Pascals (ACH50)
The number of times the volume of air in a structure will change in one hour at the induced blower door house pressure of 50 pascals.
Air Changes per Hour Natural (ACHnat) – The number of times the indoor air is exchanged with the outdoor air in one hour under natural driving forces. It can be estimated using a blower door.
Air Exchange
The process whereby indoor air is replaced with the outdoor air through air leakage and ventilation.
Air-Free Carbon Monoxide
A measurement of CO in an air sample or flue gas that takes into account the amount of excess air (oxygen, O2) in the sample, incorporating an adjustment to the as-measured CO ppm value, thus simulating air-free (oxygen-free) conditions in the sample. Usually measured in units of parts per million (ppm).
Air Handler
A steel cabinet containing a blower with cooling and/or heating coils connected to ducts that transports indoor air to and from the air handler.
Air Infiltration Barrier
A spun polymer sheet (for example, house wrap) that stops almost all the air traveling through a building cavity, while allowing moisture to pass through it.
Air Sealing
Also known as “house doctoring,” air sealing is a systematic approach to “tightening” a dwelling unit’s heated envelope (building shell) to reduce uncontrolled heat loss through air leakage points present in the shell. The prevalent technique is to perform this tightening from the interior of the home. Trained workers seal the air leakage points using a variety of materials, such as insulation, caulk, foam, vapor barriers, and weather-strip. Air leakage identification is usually aided by using diagnostic equipment like blower doors and infrared scanners, since many leakage point are not obvious to the naked eye. Part of the air sealing protocol includes testing to ensure that the building envelope is not sealed too tightly. Over-tightening can result in health and safety problems for the occupants, including back drafting of combustion equipment (furnaces, hot water heaters) and moisture condensation causing mold and mildew on surfaces.
Altitude Adjustment
The input modification for a gas appliance installed at a high altitude. When a gas appliance is installed more than 2000 feet above sea level, its input rating must be reduced by approximately 4 percent per 1000 feet above sea level.
Ambient Air
Air in the habitable space.
Ambient Lighting
Lighting spread throughout the lighted space for safety, security, and aesthetics.
American National Standards Institute, Inc. (ANSI)
A private non-profit organization that oversees the development of voluntary consensus standards for products, services, processes, systems, and personnel in the United States.
American Society of Heating, Refrigeration, and Air Conditioning Engineers (ASHRAE)
A technical society for individuals and organizations interested in heating, ventilation, air-conditioning, and refrigeration.  ASHRAE publishes standards and guidelines relating to HVAC systems and issues.
American Society for Testing and Materials (ASTM)
A standards organization that develops and publishes voluntary consensus technical standards for a wide range of materials, products, systems, and services.
A unit of measurement that tells how much electricity flows through a conductor. It is comparable to a cubic foot per second measurement of water flow. For example, a 1,200-watt, 120-volt hair dryer pulls 10 amperes of electric current (watts divided by volts).
Annual Fuel Utilization Efficiency (AFUE)
A laboratory-derived efficiency for heating appliances that accounts for chimney losses, jacket losses, and cycling losses, but not distribution losses or fan/pump energy.
Annual Return
The yearly savings divided by the initial cost needed to achieve the savings, expressed as a percent.
A heating control device that controls the burner or the circulator in a hydronic heating system
As-Measured Carbon Monoxide
A measurement of CO in a sample of air or flue gas that does not take account of the amount of excess air (oxygen, O2) diluting the CO concentration. Usually measured in units of parts per million (ppm).
A fibrous mineral with fireproof and insulation characteristics which may be shaped into a variety of building materials. Small, sharp, asbestos fibers may cause damage to lungs if they are inhaled.
Atmospheric Appliance
A combustion appliance that burns at normal atmospheric pressure. Most gas water heater burners and gas range top burners are atmospheric.
Atmospheric Pressure
The weight of air and its contained water vapor on the surface of the earth. At sea level this pressure is 14.7 pounds per square inch.
Attic Insulation
The installation of approved insulation products (rockwool, fiberglass, and cellulose) evenly across the unconditioned attic area to achieve desired levels of thermal resistance. Insulation products have manufacturer rated “R” levels (resistance to heat loss measurements). The more inches of insulation installed the higher the resistance level. The recommended “R” values vary by climatic regions of the country. It is common for weatherization programs to install a minimum of R-19 or as much as R-38 in colder regions. The cost-effective level of insulation to be added, if any, depends on the existing level of insulation in the attic. Auditors determined the amount of insulation to be added through prescriptive lists or energy audit programs that calculate the saving to investment ratio from increasing insulation levels.
Attic Preparation
This refers to the protocol for inspecting and preparing an attic area for the installation of insulation. The preparatory work is directed primarily to air infiltration and safety issues. Some of the protocols include placing barriers around heat-producing sources in the attic (electrical junction boxes, recessed lights, etc.); placing chutes by the eaves to prevent the insulation from blocking needed air ventilation paths; and sealing bypasses and other penetrations between the heated space and the unconditioned attic area.
The process of identifying energy conservation opportunities in buildings.
American Wire Gauge


Continuous spillage of combustion gases from a vented combustion appliance into the conditioned space.
Backdraft Damper
A damper, installed near a fan, that allows air to flow in only one direction.
Backer Rod
Polyethylene foam rope used as a backer for caulking.
A plate or strip designed to retard or redirect the flow of flue gases.
Balance point
The outdoor temperature at which no heating is needed to maintain inside temperatures.
Balance Heating
This is the result of balancing the airflow of the central heating distribution system so that intake and output air exists at levels to maximize efficiency. The balancing of the distribution system assures that all areas of the home being served by the same heating or cooling system or any zone within the system receive approximately equal heated or cooled air.
A coil of wire or electronic device that provides a high starting voltage for a lamp and limits the current flowing through it
Band Joist
See – Rim Joist
Barometric Vent Damper
A device installed in the heating unit vent system to control draft. Usually used on oil-fueled units or gas units with power burners
A blanket of preformed insulation, generally 14.5 inches or 22.5 inches wide, and varying in thickness from 3.5 inches to 9 inches.
A strong horizontal building support used to carry the weight of a floor or roof.
Belly Return
A configuration found in some mobile homes that uses the belly cavity as the return side of the heating/cooling distribution system.
Bimetal Element
A metal spring, lever, or disc made of two dissimilar metals that expand and contract at different rates as the temperature around them changes. This movement operates a switch in the control circuit of a heating or cooling device.
A construction element or material used to prevent the movement of air or insulation into or through building cavities.
Blower Door
A blower door is a diagnostic tool used to locate the points of infiltration in the building envelope and help prioritize the air sealing protocols. This device can be mounted in an exterior door or window opening. The blower door uses a calibrated, powerful, variable speed fan to pressurize or depressurize the dwelling. Its adjustable frame allows the fan assembly to fit snugly in most frames. Air movement and pressure differentials are measured using a set of gauges attached to the frame and fan. These calculations of air movement allow technician to quantify the level of leakage. Such leakage measurements are usually expressed in terms of equivalent leakage area (ELA), air changes per hour (ACH), and cubic feet per minute of airflow (CFM). Any one or more of these measurements can help determine levels of air leakage, indoor air quality, and amount of sealing work to be performed. In addition to measuring air movement, the blower door will exaggerate the leakage points in the building shell for easy identification. This diagnostic tool, when used in conjunction with an infrared scanner, produces even more accurate results.
The act of removing water from a boiler to remove sediment and suspended particles.
Blower Fan
The squirrel-cage fan in a furnace or air handler.
Blown Insulation
A loose-fill insulation that is blown into attics and building cavities using an insulation blowing machine.
A fossil fuel appliance used for producing hot water or steam as the medium to distribute heat to the dwelling unit.
A duct section that connects between a duct and a register or between round and square ducts
Branch Circuit
An electrical circuit used to power outlets and lights within a home.
The intensity of the sensation derived from viewing a lit surface. Measured in footlamberts, it is also called luminance or luminous intensity.
British Thermal Unit (Btu)
The quantity of heat required to raise the temperature of one pound of water one degree Fahrenheit.
BTUh – British Thermal Units per hour.
Building Cavities
The spaces inside walls, floors, and ceilings between the interior and exterior sheeting
Building Envelope
The area of the building that encloses conditioned space. Only the exterior four walls to the ceiling under the attic and the floor above the unheated basement area are considered part of the building envelope. The floor of a unit that is built on stilts or is above an unheated crawl space is considered a part of the building envelope. The roof of a building that has no ceilings (or that is part of the ceiling) is considered part of the building envelope.
Building Science
A complex perspective on buildings, using contemporary technology to analyze and solve problems of design, construction, maintenance, safety, and energy efficiency.
Building Tightness Limit (BTL)
Calculation procedure, expressed in units of CFM50, based on the American Society of Heating, Refrigerating and Air- Conditioning Engineers Standard 62-2001, Ventilation for Acceptable Indoor Air
Quality. This method was clearly explained in an article in Home Energy magazine, (Tsongas 1993). The method closely follows the parameters set in ASHRAE 62-2001: For acceptable indoor air quality, 15 CFM per person (set minimum of 5 people) or 0.35 air changes per hour (ACH), whichever is greater, must be supplied by natural air leakage and/or continuously operating ventilation.
A device that facilitates the burning of a fossil fuel, like gas or oil.
An air leakage site that allows air to leak out of a building passing around the air barrier and insulation.


Carbon Dioxide (CO2)
A heavy, colorless, nonflammable gas formed by the oxidation of carbon, by combustion, and by the respiration of plants and animals.  One of two main products of complete combustion of a hydrocarbon (the other is water vapor).
Carbon Monoxide (CO)
Carbon Monoxide is a tasteless, odorless, colorless and poisonous gas that is a by-product of incomplete combustion of fossil fuels. It is usually caused by a lack of air to support combustion or impingement of the flame.
Exposed molding or trim around a window or door.
Mastic compound for filling joints and cracks.
Category I Fan-Assisted Gas Appliance
An appliance that operates with negative static pressure in the vent, a temperature that is high enough to avoid condensation in vent, and an integral fan to draw a controlled amount of combustion supply air through the combustion chamber.
Category I Gas Appliance
An appliance that operates with negative static pressure in the vent and a temperature that is high enough to avoid condensation in vent.
Category II Gas Appliance
An appliance that operates with negative static pressure in the vent and a temperature that is low enough to cause excessive condensation in the vent.
Category III Gas Appliance
An appliance that operates with positive static pressure in the vent and a temperature that is high enough to avoid condensation in vent.
Category IV Gas Appliance
An appliance that operates with positive static pressure in the vent and a temperature that is low enough to cause excessive condensation in the vent. Comment: Airtight vent connector;
Cellulose Insulation
Insulation, packaged in bags for blowing, made from newspaper or wood waste and treated with a fire retardant
A temperature scale on which water freezes at 0 degrees and boils at 100 degrees
Central Heating System
This refers to the primary heating system of the dwelling unit including the heat producing appliance, the return and supply system for heat distribution, and ducts or pipes for flue gas ventilation. Central heating systems usually do not include wood stoves, kerosene heaters, space heaters, and electric baseboard heating units.
This term means the amount of cubic feet per minute of air moving through a structure and measured at 50-pascal pressure.

The cubic feet of air flowing through a house from indoors to outdoors during typical, natural conditions. This figure can be roughly estimated using a blower door.


CFM Per Person or Per Room
An estimate of the cubic feet per minute of fresh air available or required per occupant or per room.


CFM – Cubic Feet per Minute
Usually seen as CFM 50, cubic feet per minute of air movement due to 50 pascal house/outdoor pressure differential.
A building component designed for the sole purpose of assuring combustion by-products are exhausted to the exterior of the building.
Chimney Flue
A passageway in a chimney for conveying combustion gases to the outdoors.
Circuit Breaker
A device found in a Circuit Panel Box that completes an electric circuit. This breaker disconnects the circuit from electricity when it senses an overload of current.
Clean and Tune (C&T)
A procedure performed on a heating system by a licensed furnace service technician to maximize the appliance efficiency using existing hardware. The C&T is usually preceded by a combustion efficiency test to assess whether other conditions exist requiring extensive furnace work. The C&T can involve a variety of activities to upgrade the efficiency and safe operation of the heating system. These can include pilot and burner adjustment, adjustment of ventilation and combustion, check and reset controls, inspect filters, lubricate motors, flush low water cut-off, check operation of steam and water relief valves, check thermostat, check safety valve, and check thermocouple.
Cleanout Opening
An opening in a chimney (usually at its base) to allow inspection and the removal of ash or debris.
Circuit Breaker
A device that automatically disconnects an electrical circuit from electricity under a specified or abnormal condition of current flow.
Co-efficient of Performance (COP)
A heat pump or air conditioner’s output in watt-hours of heat moved divided by watt-hours of electrical input.
A snake-like piece of copper tubing surrounded by rows of aluminum fins that clamp tightly to the tubing and aid in heat transfer.
Cold Air Return (return side)
Ductwork through which house air is drawn for reheating during a furnace’s cycle.
Color Rendering Index (CRI)
A measurement of a light source’s ability to render colors the same as sunlight. CRI has a scale of 0 to 100.
Color Temperature
A measurement of the warmness or coolness of a light source in the Kelvin temperature scale.
A vertical building support usually made of wood or steel.
Means something will burn, although not necessarily readily.
Combustible Gas Leak Detector
A device for determining the presence and general location of combustible gases in the air.
The act or process of burning. Oxygen, fuel, and a spark must be present for combustion to occur.
Combustion Air
Air that chemically combines with a fuel during the combustion process to produce heat and flue gases, mainly carbon dioxide and water vapor.
Combustion Analyzer
A device used to measure and analyze combustion gases for efficiency and safety in heating units.
Combustion Appliance
Any appliance in which combustion occurs.
Combustion Appliance Zone (CAZ)
The closed space or area that holds one or more combustion appliances.
Combustion Chamber
The area inside the heat exchanger where the flame burns
Combustion Test
This test is performed to determine the efficiency at which a heating appliance is operating at steady state. The actual tests or sequence of tests may vary in conjunction with the type of testing equipment used or the type of heating appliance being tested. Persons performing these tests must be extremely familiar with the testing equipment being used and must be trained in conducting the tests. In some states, a license is required to perform such tests.
Common Vent
The portion of the vent or chimney through which passes products of combustion from more than one appliance.
Compact Fluorescent Lamp (CFL)
A small fluorescent light engineered to fit conventional incandescent fixtures.
A motorized pump that compresses the gaseous refrigerant and sends it to the condenser where heat is released
Concentrically Constructed Direct-Vent
A direct-vent appliance that has an exhaust-gas vent and a combustion-supply-air vent arranged in a concentric fashion, i.e., one vent is inside the other with a space between the walls of each.
When a gas turns into a liquid as it cools, it condenses. Condensation is the opposite of evaporation. When a gas condenses into a liquid it releases heat.
The coil in an air conditioning system where the refrigerant condenses and releases heat, which is then carried away by air moving through the coil.
Vapor condensed back to a liquid.
Condensate Receiver
A tank for catching returning condensate water from a steam heating system.
Intentionally heated or cooled areas of a building
The quantity of heat, in BTUs, that will flow through one square foot of material in one hour, when there is a one degree Fahrenheit temperature difference between both surfaces. Conductance values are given for a specific thickness of material.
Conduction is the transfer of heat through a material by molecular movement. Reducing heat loss through conduction can include the installation insulation in wall, ceiling, and floor cavities, insulation of hot water tanks, creating thermal breaks in window and door framing, and sealing of bypasses and other sources of air movement.
The quantity of heat that will flow through one square foot of homogeneous material, one inch thick, in one hour, when there is a temperature difference of one degree Fahrenheit between its surfaces.
Confined Space
A space with a volume of less than 50 cubic feet per 1,000 BTU per hour of the total input rating of all combustion appliances installed in that space.
Difference in brightness measured by the relationship between an object’s brightness and the brightness of its background.
Control Circuit
A device that opens and closes a power circuit or opens and shuts a valve.
The transfer of heat caused by the movement of a fluid like water or air. When a fluid becomes warmer it becomes lighter and rises.
Convective Air Flow
Air movement where less dense (warmer) air is displaced by more dense (cooler) air. Often expressed by the phrase “hot air rises.” Convective air flow can be useful if controlled, as in gravity hot air heating systems, but is more often a contributor to heat loss.
Convective Loop
A structural heat loss resulting from temperature differences between the inside and outside wall surfaces causing an air movement loop within the wall cavity. This condition can be present when a stud cavity has no insulation. Air in the cavity is heated near the interior surface of the wall, rises, circulates back toward the exterior siding, falls, re-circulates back to the warm side, is re-heated, and so on.
Conventionally Vented Combustion Appliance
Combustion appliances that are characterized by atmospheric burners or natural draft. Sealed or direct-vent appliances are not conventionally vented.
Cooling Load
The maximum rate of heat removal required of an air conditioner when the outdoor temperature and humidity are at the highest expected level.
Cost Effective
Having an acceptable payback, return-on-investment, or savings-to-investment ratio.
Critical Framing Juncture
An intersection of framing members and envelope components that require special attention during prep and installation of insulation.
Cross Section
A view of a building component drawn or imagined by cutting through the component.
CSBG – Community Services Block Grant
The Community Services Block Grant (CSBG) is federal, anti-poverty block grant which funds the operations of a state-administered network of local agencies. This CSBG network consists of more than 1,100 agencies that create, coordinate and deliver programs and services to low-income Americans in 96% of the nation’s counties.
Most agencies in the CSBG network are Community Action Agencies (CAAs), created through the Economic Opportunity Act, a predecessor of the CSBG. Community representation and accountability are hallmarks of the CSBG network, where agencies are governed by a tri-partite board. This structure consists of elected public officials, representatives of the low-income community, and appointed leaders from the private sector. Because the CSBG funds the central management and core activities of these agencies, the CSBG network is able to mobilize additional resources to combat the central causes of poverty.
Cubic Foot Per Minute (CFM)
A measurement of air movement past a certain point or through a certain structure
Cubic Feet Per Minute50 (CFM50)
The number of cubic feet per minute of air flowing through the fan housing of a blower door when the house pressure is 50 Pacals (0.2 inches of water column). This figure is the most common and accurate way of comparing the tightness of buildings that are tested using a blower door.
Cubit Feet Per Minutenat (CFMnat)
The number of cubic feet of air flowing through a house from indoors to outdoors during typical, natural conditions. This figure can be roughly estimated using a blower door using the LBL (Lawrence Berkeley Labs) infiltration model.
Curtain Wall
A wall between columns and beams that supports no weight but its own
Customer Certification
A final determination concerning program eligibility based on income and ownership, resulting in the customer’s receipt or denial of WAP benefits.


A rectangular groove cut into wood.
The wood material installed under roofing material to support the roofing.
Degree Days (DD)
A measure of outdoor temperature produced by adding the temperature differences between the inside (65°F) and the daily average outside temperature for a one-year period.
Demand for Energy
The peak need for electrical energy. Some utilities levy a monthly charge for demand.
Demand Side Management (DSM)
The planning and implementation of those utility sponsored activities designed to influence customer use of electricity or gas in ways that will produce desired changes in the utility’s load shape, such as changes in the pattern and magnitude of the utility’s load. DSM study has resulted in a variety of utility-sponsored programs to redirect their customer’s usage patterns, especially in the peak load periods. While mainly an electric utility applied concept, there is some application to gas utilities as well. The ultimate goal for most utilities is to avoid the need to invest in new power plants or distribution due to excessive demands on current capacity.
The weight of a material divided by its volume, usually measured in pounds per cubic foot.
Cause to have a lower pressure or vacuum with respect to a reference of a higher pressure.
A liquid or solid material used to absorb water or water vapor.
Design Temperature
A high or low temperature used for designing heating and cooling systems when calculating the building load.
Dew Point
The warmest temperature of an object in an environment where water condensation from the surrounding air would form on that object
Dilution Air
Air that enters through the dilution device-an opening where the chimney joins to an atmospheric-draft combustion appliance
Dilution Device
A draft diverter, draft hood, or barometric draft control on an atmospheric-draft combustion appliance.
Direct-Vent Appliance
A combustion appliance for which all combustion gases are vented to the outdoors through an exhaust vent pipe and all combustion supply air is vented to the combustion chamber from the outdoors through a separate, dedicated supply-air vent.
Distribution System
This term refers to that part of a central heating system used to deliver heated transfer media to the living space, and return the cooled transfer media to the appliance for re-heating. In a forced air system this includes the blower, ducts, registers, dampers, and cold air returns. In a hot water system this includes circulators, supply lines, radiators, and return lines.
Domestic Hot Water (DHW)
Refers to a separate, closed system to heat potable (drinkable) water and supply it to the dwelling unit for washing, bathing, etc.
A framed structure projecting above a sloping roof surface, and normally containing a vertical window.
A pressure difference that causes combustion gases or air to move through a vent connector, flue, chimney, or combustion chamber.
Draft Diverter
A device located in gas appliance flue pipe. Used to moderate or divert draft that could extinguish the pilot or interfere with combustion
Draft Fan
A mechanical fan used in a venting system to augment the natural draft in gas- and oil-fired appliances. These electrically operated, paddle-fan devices are installed in vent connectors.
Draft Hood
A nonadjustable device built into an appliance or a part of the vent connector that is intended to 1) provide for escape of flue gases if blockage or backdraft occurs, 2) prevent a downdraft of outdoor air from entering the appliance, 3) neutralize the effect of stack action of the chimney, and 4) lower the dew point temperature of the flue gas by the infusion of ambient room air.
Draft Regulator
A self-regulating damper attached to a chimney or vent connector for the purpose of controlling draft. A draft regulator can reduce draft; it cannot increase draft.
Gypsum interior wallboard used to produce a smooth and level interior wall surface and to resist fire. Also called gypsum wall board or sheetrock.
Dry Bulb Temperature
Normal ambient air temperature measured by a thermometer.
Duct Blower
A blower-door-like device used for testing duct leakiness and air flow.
Duct Zone
A building space or cavity that contains heating or cooling ducts.
Any structure which consists of two separate dwelling units in one building.
Dwelling Unit
A house, including a stationary mobile home, an apartment, a group of rooms, or a single room occupied as separate living quarters.



The part of a roof that projects beyond its supporting walls (See – Soffit)
The ratio of output divided by input
The number of lumens produced by a watt used for lighting a lamp. Used to describe lighting efficiency.
Electric Service
The electric meter and main switch, usually located outside the building.
Eligible Multifamily Dwelling Units
A multifamily building qualifies to be weatherized in its entirety when 66% (50% for 2 and 4 unit buildings) or more of the total dwelling units in the building are determined to be eligible as per DOE rules.
Eligible Unit
A unit occupied by a household that is categorically eligible or income eligible by DOE and/or LIHEAP standards.
The rate that a material emits radiant energy from its surface. Also called emissivity.
Any covering or coating that acts as a barrier between the hazard (e.g., lead-based paint) and the environment, the durability of which relies on adhesion and the integrity of existing bonds between existing layers (e.g., paint) and the substrate.
The building shell. The exterior walls, floor, and roof assembly of a building. Also referred to as building envelope.
A quantity of heat or work
Energy Audit
The process of identifying energy conservation opportunities in buildings.
Energy Consumption
The conversion or transformation of potential energy into kinetic energy for heat, light, electricity, etc.
Energy Education
The process used by WAP staff to inform customers of the ways they can further reduce energy consumption through altering their behavioral patterns. The most effective protocol includes multiple interaction and reinforcement with the household residents and use of a negotiated and written action plan.
Energy Efficiency
Term used to describe how efficiently a building component uses energy.
Energy Efficiency Ratio (EER)
A measurement of energy efficiency for room air conditioners. The EER is computed by dividing cooling capacity, measured in British Thermal Units per hour (Btuh), by the watts of power. (See – Seasonal Energy Efficiency Rating or SEER)
The internal heat of a material measured in Btus per pound.
Heat unavailable to a closed thermodynamic system during a heat transfer process.
The building shell. The exterior walls, floor, and roof assembly of a building. Also referred to as building enclosure.
Environmentally Sensitive
Highly susceptible to adverse effects of pollutants.
EPA , U.S. Environmental Protection Agency
EPA’s mission is to protect human health and to safeguard the natural environment – air, water, and land – upon which life depends. For 30 years, EPA has been working for a cleaner, healthier environment for the American people.
Equivalent Leakage Area (ELA)
Calculation, in square inches, of the total area of all holes and cracks in a structure. The leakage area is then accumulated to represent one total leakage point.
The change that occurs when a liquid becomes a gas. Evaporation is the key process in the operation of air conditioners and evaporative coolers.  Evaporation is a cooling process.
Evaporative Cooler
A device for cooling homes in dry climates by humidifying and cooling incoming air by the evaporation of water.
The heat transfer coil of an air conditioner or heat pump that cools the surrounding air as the refrigerant inside the coil evaporates and absorbs heat.
This term describes the movement of air out of a building. Often refers to warm air leaving a building due to pressurization, infiltration, wind, stack effect, and/or convective flow.


A temperature scale used in the United States and a few other countries. On the Fahrenheit scale, water boils at 212 degrees and freezes at 32 degrees.
Family Unit
All persons living together in a dwelling unit
Fan-Assisted Combustion
A combustion appliance with an integral fan to draw combustion supply air through the combustion chamber.
Fan Control
A bimetal thermostat that turns the furnace blower on and off as it senses the presence of heat.
Fan-Off Temperature
In a furnace, the supply air temperature at which the fan control shuts down the distribution blower.
Fan-On Temperature
In a furnace, the supply air temperature at which the fan control activates the distribution blower.
Federal Energy Management Program (FEMP)
A program of DOE that implements energy legislation and presidential directives. FEMP provides project financing, technical guidance and assistance, coordination and reporting, and new initiatives for the federal government. It also helps federal agencies identify the best technologies and technology demonstrations for their use.
Feeder Wires
The wires connecting the electric meter and main switch with the main panel box indoors.
Window and door openings in a building’s wall.
A fibrous material made by spinning molten glass used as an insulator and heat loss retardant.
Fill Tube
A plastic or metal tube used for its stiffness to blow insulation inside a building cavity.
Fin Comb
A comb-like tool used to straighten bent fins in air conditioning coils.
Fire Stop
Framing member designed to stop the spread of fire within a wall cavity.
Flame Safety Control
A control device used to stop the flow of fuel to the burner assembly in the event of no ignition.
Combustible; readily set on fire.
Waterproof material used to prevent leakage at intersections between the roof surface at walls or penetrations.
Floor Joists
The framing members that support the floor area.
The channel of pipe used to control air flow of combustion gases.
Foam Board
Plastic foam insulation manufactured most commonly in 4’x8′ sheets in thickness of 1/4″ to 3″.
Foot Candle
A measure of light striking a surface.
The part of a foundation system that actually transfers the weight of the building to the ground.
Forced Draft
A vent system for which a fan installed at the combustion appliance moves combustion gases to the outdoors with positive static pressure in the vent pipe. Because of this positive pressure, the vent connector must be air-tight.
Easily broken into small fragments or reduced to powder, e.g., as with asbestos
Frost Line
The maximum depth of the soil where water will freeze during the coldest weather
An appliance for heating a medium to distribute heat throughout the dwelling unit.
Thin wood strips fastened to a wall or ceiling surface as a nailing base
for finish materials.


The triangular section of an end wall formed by the pitch of the roof.
Gable Roof
A roof shape that has a ridge at the center and slopes in two directions.
Gas Heating System
A heating system that uses natural gas or bottled liquid propane gas as fuel
Gas Oven Bake Burner
Oven burner used for baking located just below the oven compartment floor.
Gas Oven Broiler Burner
Oven burner used for broiling located at the top of the oven compartment.
Elastic strip that seals a joint between two materials.
Glass Load Factor
A number combining glass’s solar heat transmission and its heat conduction. Used for cooling load calculations.
Glass installation. Pertaining to glass assemblies or windows
Glazing Compound
A flexible, putty-like material used to seal glass in its sash or frame.
Gravity Furnace
A central heating system that uses natural gravity to distribute heat throughout the dwelling unit as opposed to forced circulation, pumps, or circulation blowers.
Ground Fault Circuit Interrupter (GFI or GFCI)
An electrical connection device that breaks a circuit if a short occurs. These are required for all exterior use of electrical equipment, or when an electrical outlet is located near a water source.
A metal or wood plate added to the surface of a joint to strengthen the connection.
Gypsum Board
A common interior sheeting material for walls and ceilings made of gypsum rock powder packaged between two sheets of heavy building paper. Also called sheetrock, gyprock, or gypboard.


Habitable Space
A building space intended for continual human occupancy.  Examples include areas used for sleeping, dining, and cooking, but not bathrooms, toilets, hallways, storage areas, closets, or utility rooms. See
occupiable space and conditioned space.
Handicapped Person
Any individual who is: 1) handicapped as defined in Section 7 (6) of the Rehabilitation Act of 1973; 2) under a disability as defined in Section 1614 (1) (3) (A) or 223 (d) (i) of the Developmental Disabilities Services and Facilities Construction Act; or 3) who is receiving benefits under Chapter 11 or 15 of Title 38, U.S.C. Other conditions may apply state to state, which can deem an individual as handicapped for the purposes of the WAP.s
Hazardous Condition
A situation that is causing a danger to the client/crew/contractor that exists before, is created by, or is exacerbated by, weatherization. For example, a dwelling could have a moisture problem that is allowing biological hazards (molds, viruses, bacteria, etc.) to flourish. Another example would be fiberglass entering the conditioned space due to improperly fastened or sealed ductwork.
Hazardous Material
A particular substance that is considered a danger to the sclient or crew.
Heating Degree Day(s) (HDD)
The number of degrees per day that the daily average temperature (the mean of the maximum and minimum recorded temperatures) is below a base temperature, usually 65 degrees Fahrenheit, unless otherwise specified; used to determine indoor space heating requirements and heating system sizing. Total HDD is the cumulative total for the year/heating season. The higher the HDD for a location, the colder the daily average temperature(s).
Heat Anticipator
A very small electric heater in a thermostat that causes the thermostat to turn off before room temperature reaches the thermostat setting, so that the house does not overheat from heat remaining in the furnace and ducts after the burner shuts off.
Heat Capacity
The quantity of heat required to raise the temperature of 1 cubic foot of a material 1 degree F.
Heat Exchanger
The device in a heating unit that separates the combustion chamber from the distribution medium and transfers heat from the combustion process to the distribution medium.
Heat Gains
Term used to mean unwanted heat that accumulates in homes, making mechanical cooling desirable or necessary.
Heat Loss
The amount of heat escaping through the building shell as measured for a specific period of time (month, year, etc.)
Heat Pump
A type of heating/cooling unit, usually electric, that uses a refrigerant fluid to heat and cool a space.
Heat Rise
The number of degrees of temperature increase that air is heated as it is blown over the heat exchanger. Heat Rise equals supply temperature minus return temperature.
Heat Transmission
Heat flow through the walls, floor, and ceiling of a building, not including air leakage.
Heat Transfer Coefficient
See U-value.
Heating Degree Day
Each degree that the average daily temperature is below the base temperature (usually 65 degrees F) constitutes one heating degree day.
Heating Load
The maximum rate of heat conversion needed by a building during the very coldest weather.
Heating Seasonal Performance Factor (HSPF)
Rating for heat pumps describing how many Btus they transfer per kilowatt-hour of electricity consumed.
High Limit
A bimetal thermostat that turns the heating element of a furnace off if it senses a dangerously high temperature.
Hip Roof
A roof with two or more contiguous slopes, joined along a sloping “hip.”
Home Energy Index
The number of BTUs of energy used by a home, divided by its area of conditioned square feet and by the number of heating degree days during one year.
Home Energy Rating Systems (HERS)
A nationally recognized energy rating program that give builders, mortgage lenders, secondary lending markets, homeowners, sellers, and buyers a precise evaluation of energy losing deficiencies in homes. Builders can use this system to gauge the energy quality in their home and also to have a star rating on their home to compare to other similarly built homes.
Home Heating Index
The number of Btus of energy used by a home divided by its area in square feet, then divided by the number of heating degree days during the time period.
HOME Program
A program created under Title II (the Home Investment Partnership Act) of the National Affordable Housing Act of 1990. Provides funds for states to expand the supply of decent and affordable housing for low-income people. This program can be easily coordinated with a state’s WAP efforts.
Home Ventilating Institute (HVI)
Any individual or group of individuals who are living together as one economic unit for whom residential energy is customarily purchased in common or who make undesignated payments for energy in the form of rent.
House Pressure
The difference in pressure between the indoors and outdoors measured by a manometer.
U.S. Department of Urban Housing and Development
An automatic control that switches a fan, humidifier, or dehumidifier on and off to control relative humidity.
Humidity Ratio
Same as “absolute humidity.” The absolute amount of air’s humidity measured in pounds of water vapor per pound of dry air.
Heating, Ventilation, and Air-Conditioning System.  All components of the appliances used to condition interior air of a building.
Hydronic System
A heating system that uses hot water or steam as the heat-transfer fluid.  Commonly called a hot-water heating system.


Indoor Air Quality.  The quality of indoor air relative to its acceptability for healthful human habitation. Assessing and ameliorating, when necessary, the quality of indoor air is a major concern of the weatherization process. In particular, all by-products of major combustion appliances must be directly evacuated to the outdoors under all operating conditions.
The light level measured on a horizontal plane in Foot Candles
In-Kind Contributions
In-kind contributions represent the value of non-cash contributions provided by the grantee, and non-Federal parties. In-kind contributions may be in the form of charges for real property and non-expendable personal property and the value of goods and services directly benefiting and specifically identifiable to the project or program.
Inaccessible Cavity
An area that is too confined to enter and/or maneuver in by an average installer/technician.
Incandescent Light
The common light bulb found in residential lamps and light fixtures and known for its inefficiency.
Inches of Water Column (IWC)
A non-metric unit of pressure difference. One IWC is equal to about 0.004 Pascals.
Inch of Water
Small air pressure differences caused by wind, blower doors, furnace fans, and chimneys are measured in inches of water (in.-H2O) in the American measurement system.
Incidental Repairs
Under DOE rules, this term refers to the repairs on a dwelling unit necessary for the effective performance or preservation of the allowable energy conservation measures to be installed. Usually, a specific dollar amount is set by a state to limit such incidental repairs.
Induced Combustion
See “Fan-Assisted Combustion”.
Induced Draft
A vent system for which a fan – installed at or very near the termination point of the vent pipe – moves the combustion gases to the outdoors with negative static pressure in the vent pipe.
Infiltration refers to the movement of air into a building through cracks and penetrations in the building envelope. Cold air often enters the structure due to depressurization, exfiltration, wind, stack effect, and/or convective airflow.
Pertaining to heat rays emitted by the sun or warm objects on earth.
Infrared Camera
A special camera that “sees” temperature differences on surfaces, allowing the user to determine if a building assembly is insulated properly. This instrument is also useful for detecting air leakage if used with a
blower door.
Infrared Thermography
The science of using infrared imaging to detect radiant energy or heat loss characteristics of a building. The infrared camera or scanner electronically senses heat radiated by objects and converts that thermal energy into images visible to the human eye. The camera or scanner, similar to a camcorder in appearance, produces varying shades of black and white images of the building structure. The darker the image, the colder the corresponding surface; the lighter areas are the hotter surfaces. Some scanners can automatically record these images on video, as well as allow the operator to record audio commentary as he/she scans the building. A certain degree of interpretation skill is required to properly assess the images being recorded. Used in conjunction with a blower door, the scanner can provide valuable data, since the pressurization or depressurization can magnify air leakage sites and thermal bypasses.
Input Rating
The measured and assigned rating indicating the level at which an energy-using device consumes electricity or fossil fuel.
The amount of solar radiation striking a surface
A material used to retard heat transfer.
Insulating Glass
Two or more glass panes spaced apart and sealed in a factory, and having a higher R-value than a single pane of glass.
Intermittent Ignition Device (IID)
A device that lights the pilot light on a gas appliance when the control system calls for heat, thus saving the energy wasted by a standing pilot.
Internal Gains
The heat generated by bathing, cooking, and operating appliances, that must be removed during the summer to promote comfort.
Intermediate Zone
A zone located between the building’s conditioned space and the outdoors, like a crawl space or attic.
Interstitial Space
Space between framing and other building components.


The side or top piece of a window or door frame.
A horizontal wood framing member that supports a floor or ceiling.
A unit of energy. One thousand joules equals 1 BTU.


A unit of electric power equal to 1000 joules per second or 3412 Btus per hour.
The most commonly used unit for measuring the amount of electricity consumed over time; one kilowatt of electricity supplied for one hour.  A unit of electric energy equal to 3600 kilojoules.
Kinetic Energy
Consisting of, or depending on, motion; distinguished from potential energy.


A light bulb.
Landlord/Tenant Agreement
Document required for completed application when applicant is a renter. The Agreement is legally binding contract, signed by the tenant, the landlord (or property owner), and the local agency specifying the role and responsibilities of each party. The basic goal of the WAP is to ensure that the benefits of the program accrue to the low-income family. A variety of standard clauses can be incorporated into the Agreement, including clauses on landlord’s inability to raise rents for specified period of time, eviction prohibition, and landlord required “participation.” Participation can take the form of actual cash, provided labor, and/or in-kind contributions.
Latent Heat
The amount of heat energy required to change the state of a substance from a solid to a liquid, or from a liquid to a gas, without changing the temperature of the substance.
A support for plaster, consisting of thin strips of wood, metal mesh, or gypsum board.
Lead-Safe Work Practices (LSW)
Work practices required by DOE for pre-1978 homes when the weatherization work will disturb more than 2 square feet of painted surface in an interior room, 10 percent of a small component such as a
baseboard or door casing, and/or when the work will disturb more than twenty square feet of painted exterior surface.
Leakage Ratio
Measurement of total square inches of infiltration area per 100 feet of building envelope surface area.
Leverage Activity
The actions of the state and local agencies to obtain and account for resources provided to supplement or supplant federal funding being used to weatherize dwelling units.
Light Quality
The relative presence or absence of glare and brightness contrast. Good light quality has no glare and low brightness contrast.
Living Space Return System
In a mobile home, a forced warm air circulation system where air returns to the air handler through the living space, rather than through ductwork or through the mobile home belly.
Local Agency
Also referred to as the subgrantee, contractor, service delivery network member, or local service provider, a local agency is a nonprofit organization or unit of local government responsible for providing WAP services in a specified political subdivision.
Short for “low emissivity”, which means the characteristic of a metallic glass coating to resist the flow of radiant heat.
Low Water Cutoff
A float-operated control for turning the burner off if a steam boiler is low on water.
A unit of light output from a lamp.



Main Panel Box
The electric service box containing a main switch, and the fuses or circuit breakers located inside the home.
Make-up Air
Air supplied to a space to replace exhausted air.
A tube with one inlet and multiple outlets, or multiple inlets and one soutlet.
A differential gauge used for measuring pressure.
Manufactured Home
A mobile home or a “double-wide” structure.
A thick creamy substance used to seal seams and cracks in building materials.
Stone, brick, or concrete block construction.
Materials Safety Data Sheet (MSDS)
A sheet containing data regarding the properties of a particular substance, intended to provide workers with procedures for handling or working with that substance in a safe manner, including  information such as physical data, toxicity, health effects, first aid, storage, disposal, and protective equipment.
Mechanical Draft
A combustion appliance with induced draft of forced draft.
To make less severe or to mollify.
Mobile Home Energy Audit (MHEA)
A software tool that predicts manufactured home energy consumption and recommends weatherization retrofit measures.
A mixture of sand, water, and cement used to bond bricks, stones, or blocks together.
A recessed area cut into the wood framing member where a hinge or wood tongue fits.


National Association for State Community Services Programs (NASCSP)
NASCSP’s mission is to assist state in responding to poverty issues. NASCSP members are state administrators of the Community Services Block Grant (CSBG) and U.S. Department of Energy’s Weatherization Assistance Program (DOE/WAP). The CSBG, administered by the states, provides core funding to local agencies to reduce poverty, revitalize low-income communities and to empower low-income families to become self-sufficient. The DOE/WAP helps low-income families reduce their energy costs by making homes more energy efficient. The local agencies funded by these programs provide a wide range of services such as weatherization, energy assistance, child care, job training, and housing. NASCSP keeps its members, the federal government, and other interested parties informed about issues related to CSBG and DOE/WAP through its publications.
National Bureau of Standards (NBS)
Renamed by the Department of Commerce as the National Institute of Standards and Technology (NIST).
National Energy Audit (NEAT)
Created by Oak Ridge National Laboratories as a DOE approved audit qualifying for the 40% materials waiver. It is a computerized auditing tool for prioritizing energy conservation measures for houses.
National Fire Protection Association (NFPA)
Creates and maintains minimum standards and requirements for fire prevention, training, and equipment, developing and publishing codes and standards such as the NFPA 70, the National Electric Code, and NFPA 54, the National Fuel Gas Code.
National Institute for Occupational Safety and Health (NIOSH)
A federal agency responsible for conducting research and making recommendations for the prevention of work-related injury and illness to help ensure safe and healthful working conditions.
Natural Draft
A vent system that relies on natural draft (buoyant air) to move combustion gases to the outdoors.
Natural Ventilation
Ventilation using only natural air movement without fans or other mechanical devices.
Net Free Vent  Area (NFVA)
The area of a vent after that area has been adjusted for insect screen, louvers, and weather covering. The free area is always less than the actual area.
An orifice for spraying a liquid like fuel oil.


People of any age living in a dwelling. Animals are not defined as occupants.
Occupational Safety and Health Administration (OSHA)
An agency of the United States Department of Labor, with a mission to prevent work-related injuries, illnesses, and occupational fatality by issuing and enforcing standards for workplace safety and health.
Occupiable Space
An enclosed space inside the pressure boundary of a room or house, and intended for human activities including, but not limited to, all habitable spaces, bathrooms, toilet rooms, closets, halls, storage and utility areas, and laundry areas. See habitable space and conditioned space.
A unit of measure of electrical resistance. One volt can produce a current of one ampere through a resistance of one ohm.
Oil Heating System
Refers to a central heating system that uses #2 fuel oil, kerosene, or residual oil as the primary fuel for heat generation.
Open-Combustion Heater
A heating device that takes its combustion air from the surrounding room air.
A hole in a gas pipe or nozzle fitting where gas or fuel oil exits to be mixed with air before combustion occurs in the heating chamber.  The size of the orifice will help determine the flow rate.
Oscillating Fan
A fan, usually portable, that moves back and forth as it operates, changing the direction of the air movement.
Output Capacity
The conversion rate of useful heat that a heating unit produces after accounting for any waste caused by the conversion of energy into heat.
Oxygen Depletion Sensor
A safety device on a heating unit that shuts off the fuel supply to the combustion chamber when oxygen is depleted.


Packaged Air Conditioner
An air conditioner that contains the compressor, evaporator, and condenser in a single cabinet.
Parts per Million (ppm)
The unit commonly used to represent the degree of pollutant concentration, where the concentrations are small.
Pascal (Pa)
A unit of measurement of air pressure. One column inch of water equals 247 pascals. Atmospheric pressure (29.92 inches of mercury) is equivalent to 102,000 PA.  2.5Pa = 0.01 inches of water column.
Payback Period
The number of years that an investment in energy conservation will take to repay its cost through energy savings.
Perimeter Pull
A technique used in attics previously insulated with batt insulation. The batts are cut back two feet from the eaves and the area is insulated with blown insulation to ensure coverage over the outer wall top plate, and to prevent wind washing of the insulation under the existing batts.
A heat-expanded mineral used for insulation.
A measurement of how much water vapor a material will let pass through it per unit of time.
Photovoltaic  (PV)
A solid-state electrical device that converts light directly into direct current electricity of voltage-current characteristics that are a function of the characteristics of the light source and the materials in and design of the device. Solar photovoltaic devices are made of various semi-conductor materials including silicon, cadmium sulfide, cadmium telluride, and gallium arsenide, and in single crystalline, multi-crystalline, or amorphous forms.
A plastic mixture of sand, lime, and Portland cement spread over wood or metal lath to form the interior surfaces of walls and ceilings.
A framing member installed horizontally to which the vertical studs in a wall frame are attached.
The piece of ductwork, usually found above the heat exchanger of a hot air furnace, that connects the air handler to the main supply duct.
Absolutely vertical at a right angle to the earth’s surface.
Laminated wood sheeting with layers cross-grained to each other.
A plastic made by the polymerization of ethylene, used in making translucent, lightweight, and tough plastics, films, insulations, vapor retarders, air barriers, etc.
A plastic foam insulation sold in sheets, similar in composition to polyurethane.
Polystyrene Insulation
A rigid plastic foam insulation, usually white, pink,  green, or blue in color.
A versatile plastic foam insulation, usually yellow in color.
Potential Energy
Energy in a stored or packaged form, like fuel oil, coal, wood, etc.
Power Burner
A burner for which air is supplied at a pressure greater than atmospheric pressure. Most oil-fired burners are power burners. Gas burners used to replace oil burners are usually power burners.
Power Draft
See “Mechanical Draft”.
A force encouraging movement by virtue of a difference in some condition between two areas.
Pressure Diagnostics
The practice of measuring pressures and flows in buildings to control air leakage, and also to ensure adequate heating and cooling air flows and ventilation.
Pressure Pan
A device used to block a duct register while measuring the static pressure behind it.
A control that turns a steam boiler’s burner on and off as steam pressure changes.
Pressure Relief Valve
A safety component required on a boiler and water heater, designed to relieve excess pressure buildup in the tank.
Prime Window
The main window installed on the outside wall consisting of fixed or moveable lights that slide on permanently fixed tracks (not to be confused with a storm window).
Priority List
The list or ranking of installation measures developed by a program to produce the most cost effective energy savings results based on a savings to investment ratio calculation.
Program Income
Income earned by the grantee from grant-supported activities, including but not limited to, income from service fees, sale of commodities, usage or rental fees, and royalties on patents and copyrights.
The study of the relationship between air, water vapor, and heat.
Framing members that sit on top of rafters, perpendicular to them, designed to spread support to roofing materials.


A measurement of thermal resistance for materials and related surfaces.
Radiant Barrier
A foil sheet or coating designed to reflect heat flows.  Radiant barriers are not mass insulating materials.
Radiant Temperature
The average reflective temperature of objects in a home, like walls, ceiling, floor, and furniture.
Heat energy that is transferred by electromagnetic energy or infrared light, from one object to another. Radiant heat can travel through a vacuum and other transparent materials.
A radioactive gas that decomposes into radioactive particles.
A roof beam that follows the roof’s slope.
Rated Ventilation
A ventilation system that has been designed and installed under the guidelines established by the American Society of Heating, Refrigeration, and Air Conditioning Engineers (ASHRAE) Standard for
Acceptable Indoor Air Quality (Standard 62).
Recovery Efficiency
A water heater’s efficiency at actually heating water to capacity level without regard to standby or distribution losses.
The ratio of lamination or radiant heat reflected from a given surface to the total light falling on it. Also called reflectivity.
Reflective Glass
Glass that has a mirror-like coating on its exterior surface to reflect solar heat. The solar heat gain coefficient of reflective glass ranges from 0.10 to 0.40.
Any of various liquids that vaporize at a low temperature, used in mechanical refrigeration.
The grille cover over a duct outlet for warm air distribution or cold air return and sometimes control the flow.
The replacement of an existing, standard light bulbs with lower wattage energy efficient bulbs like compact fluorescent lamps.
Relative Humidity
The percent of moisture absorbed in the air compared to the maximum amount possible. For instance, air that is completely saturated has 100% relative humidity.
An automatic, electrically-operated switch.
Reset Controller
Adjusts fluid temperature or pressure in a central heating system according to outdoor air temperature.
The property of a material resisting the flow of electrical energy or heat energy.
An energy conservation measure applied to an existing building or the action of improving the thermal performance or maintenance of a building.
Return Air
Air circulating back to the furnace or central air conditioning unit from the house, to be heated or cooled and supplied back to the living area.
Reweatherized Unit
Any unit that received weatherization services prior to September 30, 1994 and has received additional services under subsequent grants or allowed by current DOE regulations.
Rim Joist
The outermost joist around the perimeter of the floor framing.  Also known as “band joist” or “band board”.
Rocking on the High Limit
Refers to the gas burner being shut down by the high limit switch on a furnace, instead of being properly activated by the fan-on/fan-off control.
Room Air Conditioner
An air conditioning unit installed through a wall or window, which cools the room by removing heat and releasing it outdoors.


A movable or stationary part of a window that frames a piece of glass.
Savings-to-Investment Ratio (SIR)
SIR is computed over the lifetimes of the retrofit measures installed and expressed in terms of the net present value of the retail cost of the dwelling’s fuel. Under some methodologies, other benefits, etc. Investment usually takes into account materials, labor, and support costs. SIRs of greater than one are counted as cost effective under this DOE WAP method of determining cost-effectiveness.
Sealed Combustion Heater
A heater that draws air for combustion from outdoors and has a sealed exhaust system.  Also called a direct-vent appliance.
Seasonal Efficiency
Refers to the overall efficiency of the central heating system including on and off cycle fuel utilization and heat loss. The calculation of these factors is represented in the Annual Fuel Utilization Efficiency (AFUE) rating for the appliance. Distribution system loss is not factored into the AFUE.
Seasonal Energy Efficiency Ratio (SEER)
A measurement of energy efficiency for central air conditioners. The SEER is computed by dividing cooling capacity, measured in BTUh, by the Watts (see also Energy Efficiency Rating).
Seasonal Performance Factor (SPF)
Ratio of useful energy output of a device to the energy input, averaged over an entire heating season.
Sensible Heat
The heat required to change the temperature of a material without changing its form.
Separate Living Quarters
Living quarters in which the occupants do not live and eat with any other persons in the structure and that have either a direct access from the outside of the building or through a common hall or complete kitchen facilities for the exclusive use of the occupants. The occupants maybe a single family, one person living alone, two or more families living together, or any other group of related or unrelated persons who share living arrangements.
A bimetal switch that turns on the elements of an electric furnace in sequence.
Service Wires
The wires coming from the utility transformer to the service equipment of the building.
This term refers to the effect of insulation depressing over time and, thereby, reducing the overall energy efficiency of the materials. This process is primarily the result of using too much air when installing the blown-in insulation – commonly called “fluffing,” or the effect of long periods of time on the materials. One reason to re-inspect some work several months after installation to assess the settling factor. Settling can also occur during the installation of sidewall insulation when the cavity is not completely filled. This is usually avoided if “dense pack” protocols are followed during the installation.
Shading Coefficient (SC)
A decimal describing how much solar energy is transmitted through a window opening compared to clear single glass having an SC of 1.0. For example, reflective glass has an SC of .20 to .45.
Structural sheeting, attached on top of the framing, underneath the siding and roofing of a building. Any building material used for covering a building surface.
Sheet Metal and Air Conditioning Contractors’ National Association (SMACNA)
Common term for any building material used for covering a building surface.
See drywall.
The building’s exterior envelope including walls, floor, and roof.
A modular roofing material, usually asphalt, that is installed in overlapping rows to cover the entire roof.
Short Circuit
A dangerous malfunction in an electrical circuit where electricity is flowing through conductors and into the ground without going through an electric load, like a light or motor.
Sidewall Insulation
The process of installing insulation material, usually blown cellulose, into the non-insulated wall stud cavities of a structure to reduce heat loss. Installation is achieved by drilling one or more rows of holes into the wall, one in each stud cavity. To achieve the most effective results, a dense pack protocol is used to install “high density” insulation materials. The “packing” of the materials should be tight enough that the installer cannot move the insulation when complete. It is common to install materials at 3.5 pounds per square foot.
The bottom of a window or door frame.
Sill Box
The outer area of the floor bound by the rim joist, floor joist, sill plate, and floor.
Site-Built Home
Includes a house built on the site from building supplies, or manufactured homes assembled on the site from pieces shipped to the site on flatbed trucks. Does not include mobile homes and double-wides.
Sling Psychrometer
A device holding two thermometers that is slung through the air to measure relative humidity.
The roof section of an attic with the roof and ceiling surfaces attached to the rafters.
The underside of a roof overhang or a small lowered ceiling, as above cabinets or a bathtub.
Solar Gain
Heat from the sun that is absorbed by a building’s materials and contributes to the heating and cooling requirements of the dwelling.
Solar Heat
Radiant energy from the sun with wavelengths between 0.7 and 1 micrometers.
Solar Heat Gain Coefficient (SHGC)
The ratio of solar heat gain through a window to incident solar heat, including both transmitted heat and absorbed/radiated heat.
Solar Heat Gain Factor (SHGF)
Solar heat gain amount on a surface with a particular angle and orientation expressed in Btus per square foot per hour.
Solar Transmittance
The percent of total solar energy transmitted by a material.
A magnetic device that moves a switch or valve stem.
Sone Level
An international unit used to measure sound levels. One Sone is equivalent to the sound of a quiet refrigerator in a quiet kitchen.
Space Heating
Heating the living spaces of the home with a room heater or central heating system.
Horizontal distance between supports.
Specific Heat
The ratio of the heat storage capacity of a particular material to the heat storage capacity of water.
Temporary flow of combustion gases from a dilution device.
A strip of vinyl, rubber, or plastic that, when inserted into a groove, holds a screen or plastic film in place on a frame.
Split-System Air Conditioner
An air conditioner having the condenser and compressor outdoors and the evaporator indoors.
Stack Effect
The term describes the effect of higher pressure at the top of a structure, lower pressure at the bottom of a structure, and neutral pressure somewhere in between, relative to the ambient (surrounding) air pressure. It is usually the result of different densities of warmer and cooler air (convective airflow).
Standing Loss
Heat loss from a hot water storage tank through its shell.
Steady State Efficiency (SSE)
The measurement of heat system balance in the on-cycle when heat into system equals heat out. Generally provided as a percentage of the maximum available heat generation capacity (100%) against the amount of usable heat being sent to the distribution system. This figure can also represent the percentage of heat being used within the system as compared to the heat lost through the flue. The reading is most valid when the stack temperature becomes constant and the distribution pumps or blowers are operating.
Steam Trap
An automatic valve that closes to trap steam in a radiator until it condenses.
Steam Vent
A bimetal-operated air vent that allows air to leave steam piping and radiators, but closes when steam strikes the surface.
A thin, trim board for windows and doors to close against or slide against.
Strike Plate
The metal plate attached to the door jamb that the latch inserts into upon closing.
A vertical wood or metal framing member used to build a wall.
The sheathing over the floor joists and under the floor covering.
Supply Air
Air that has been heated or cooled and is moved through the ducts and to the supply registers of a home.
Suspended Ceiling
Modular ceiling panels supported by a hanging frame.


Taped Duct Test (TDT)
A procedure using the blower door to measure the “potential” for leakage reduction of the duct system. All supply registers and return grills are taped shut following the initial blower door reading and a subsequent air leakage test taken. if closing off the duct system in this manner causes an appreciable reduction in the air leakage rate, this is an indication that there are significant duct leaks.
A unit of energy equal to 100,000 Btus or 29.3 kilowatt-hours.
Thermal Break
A relatively low heat/cold conductive material separating two highly conductive materials, installed to reduce heat flow through the assembly.
Thermal Bridging
Rapid heat conduction resulting from direct contact between very thermally conductive materials like metal and glass.
Thermal Boundary
A ceiling/roof, wall, floor, window, or door that separates the habitable, occupiable, and conditioned spaces from the outdoor weather. The thermal boundary should be air sealed and/or insulated if it is cost-effective to do so. Exterior doors are always examples of thermal boundaries. An attic floor is most often an example of a thermal boundary.
Thermal Bypass
Similar to a convection loop, this structural heat loss is characterized by heated air traveling up exterior or interior stud cavities and leaking out the top of that cavity to the attic through joints and cracks in the framing, wiring and plumbing holes, etc. These types of heat loss sources are sometimes the most difficult to locate.  An indirect penetration that tends to reduce the effectiveness of insulation by allowing conditioned air to move out of a structure, or allowing unconditioned air to move in.
Thermal Conductance
A material’s ability to transmit heat; the inverse of the R-Value (see U-factor).
Thermal Enclosure
The boundaries of a dwelling that serve to envelop the space to be kept warm during cold weather and cool during warm weather. The surfaces of the thermal enclosure usually serve as a thermal and pressure barrier.
Thermal Resistance
R-value; a measurement expressing the ability to retard heat flow.
A bimetal-junction electric generator used to keep the safety valve of an automatic gas valve open.
The science of heat.
A device used to control a heating or cooling system to maintain a set temperature.
Through-the-Wall Vented
Combustion appliances that are vented through a wall rather than into a vertical-rise chimney or vent. Such appliances are usually Category III or IV, but might also be Category I (e.g., direct-vent Category I water heater).
Title XVI
Term to be used interchangeably with those income groups known as SSI (Supplemental Security Income) recipients.
Tracer Gas
A harmless gas used to measure air leakage in a building.
A double coil of wire that increases or decreases voltage from a primary circuit to a secondary circuit.
Decorative wood that covers cracks around window and door openings and at the corners where walls meet floors and ceilings. Sometimes called molding.
A braced framework usually in the shape of a triangle to form and support a roof.
Type IC Recessed Electrical Fixture
An electrical fixture that is rated to be in direct contact with thermal insulation.


The total heat transmission in BTUs per square feet per hour with a 1°F temperature difference between the inside and the outside; the thermal conductance of a material.
Ultraviolet Radiation
Light radiation having wavelengths beyond the violet end of the visible spectrum; high frequency light waves.
Unconditioned Space
An area within the building envelope not intentionally or unintentionally heated.
Sheeting installed to provide a smooth, sound base for a finish material.
Underwriter’s Laboratory (UL)


Vapor Barrier
A material that retards the passage of water vapor.
Vapor Diffusion
The flow of water vapor through a solid material.
Vapor Retarder
A vapor barrier.
To change from a liquid to a gas.
Veiling Reflection
Light reflection from an object or task that obscures details.
The outer layer of a building component (e.g., interior doors often have a wood veneer; some wood-frame houses have brick veneer walls, etc.).
Vent Connector
The vent pipe carrying combustion gases from the appliance to a vent or chimney.
Vent Damper
An automatic damper powered by heat or electricity that closes the chimney while a heating device is off.
The removal of combustion gases by a chimney.
Venting System
A continuous passageway from a combustion appliance to the outdoors through which combustion gases can safety pass.
Refers to the controlled air exchange within a structure. All dwellings must “breathe” and proper ventilation rates must be determined. If the structure requires more interior/exterior air exchanges, there are mechanical and non-mechanical options for increasing those rates. The most common option is passive ventilation through the installation of roof, soffit, or gable vents.
A heat-expanded mineral used for insulation.
Visible Transmittance
The percent of visible light transmitted by a glass assembly.
Polyethylene film vapor barrier.
A unit of electromotive force. It is the amount of force required to steady current of one ampere through a resistance of one ohm. Electrical systems of most homes in the United States have 120-volt systems.


Watt (W)
A unit of measure of electric power at a point in time, as capacity or demand. One Watt of power maintained over time is equal to one joule per second.
One Watt of power extended for one hour. One thousandth of a kilowatt-hour.
Weatherization – The process of reducing energy consumption and increasing comfort in buildings by improving the energy efficiency of the building and maintaining health and safety.
Weatherization Assistance Program (WAP)
DOE’s Weatherization Assistance Program is the nation’s largest residential energy efficiency program. Its mission is to increase the energy efficiency of dwellings occupied by low-income Americans, thereby reducing their energy costs, while safeguarding their health and safety.
DOE works directly with the states, U.S. Territories, the District of Columbia, and Native American Tribal Governments to carry out these goals. These Grantees, in turn, contract with approximately 1,000 local governmental or non-profit agencies to deliver weatherization services to our low-income clients.
Flexible gaskets, often mounted in rigid metal strips, for limiting air leakage at openings in the shell like doors and windows.
A reinforcing fabric used with mastics and coatings to prevent patches from cracking.
Weep Holes
Holes drilled for the purpose of allowing water to drain out of an area in a building where it has accumulated.
Wet-Bulb Temperature
The temperature of a dampened thermometer of a Sling Psychrometer used to determine relative humidity, dew point, and enthalpy.

Whole House Weatherization
A concept that addresses the house as a single energy consuming system, rather than a loose collection of unrelated systems.  The whole house approach is based on a sophisticated analyses of individual homes, to maximize energy and dollar savings.


Window Films
Plastic films coated with a metallic reflective surface that are adhered to window glass to reflect infrared  rays from the sun.

Window Frame
The sides, top, and sill of the window forming a box around window sashes and other components.
Worst-Case Depressurization Test
A safety test, performed by specific procedures, designed to assess the probability of chimney back-drafting.  A condition created when 1) all exhaust appliances (bathroom exhaust, kitchen exhaust, vented dryers, etc.) are operating, 2) the interior doors of a house are in a position that causes the
greatest negative pressure in the Combustion Appliance Zone, and 3) the furnace air handler is operating (if such operation causes increased negative pressure in the Combustion Appliance Zone).





A room or portion of a building separated from other rooms by an air barrier.