Glossary
A
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 at 50 pascals (ACH50)
The number of times that the complete volume of a home is exchanged for outside air when a blower door depressurizes the home to 50 pascals.
Air Duct
A hollow tube (square or round) that circulates air from a forced-air heating and/or cooling system to a room (supply duct) or returns air back to the main system from a room (return duct).
Air handler
A steel cabinet containing a blower with cooling and/or heating coils connected to ducts.
Assessment
The process of identifying energy efficiency opportunities in buildings.
Annual fuel utilization efficiency (AFUE)
A laboratory-derived efficiency rating for heating appliances which accounts for chimney losses, jacket losses, and cycling losses.
Air Leak
A hole, crack or gap where air can leak in or out of a house. Air leaks can make a home feel drafty or uncomfortable and waste energy.
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B
Backdrafting
Continuous spillage of combustion gases from a combustion appliance.
Batt
A narrow blanket of fiberglass insulation, often 14.5 or 22.5 inches wide.
Blower door
A device that consists of a fan, a removable panel, and gauges used to measure and locate air leaks.
Boot
A duct section that connects between a duct and a register.
British thermal unit (Btu)
The quantity of heat required to raise the temperature of one pound of water one degree Fahrenheit.
Building Science
Branch of science dealing with construction, maintenance, safety, and energy efficiency of buildings.
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C
Capillary action
The ability of water to move through materials, even upward against gravity, through small tubes or spaces.
Capillary barrier
A material or air space designed to stop capillary action from carrying water into a building.
Carbon dioxide
One of two main products of complete combustion of a hydrocarbon (the other is water vapor).
Carbon monoxide
An odorless and poisonous gas produced by incomplete combustion.
Caulking
A mastic compound for filling joints and cracks.
Cellulose insulation
Insulation, packaged in bags for blowing, made from newspaper or wood waste and treated with a fire retardant.
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 pascals (0.2 inches of water). This figure is the most common and accurate way of comparing the airtightness of buildings that are tested using a blower door.
Coefficient of performance (COP)
A heat pump or air conditioner's output in watt-hours of heat moved divided by watt-hours of electrical input.
Coil
A snakelike piece of copper tubing surrounded by rows of aluminum fins that clamp tightly to the tubing in order to aid in heat transfer.
Combustion air
Air that provides oxygen for combustion.
Compressor
A motorized vapor pump that compresses the gaseous refrigerant and sends it to the condenser where collected heat is released.
Condense
when a gas turns into a liquid as it cools, we say it condense. Condensation is the opposite of evaporation.
Condenser
The coil in an air conditioning system where the refrigerant condense and releases heat.
Conditioned
Intentionally heated or cooled areas of a building are conditioned.
Conduction
Heat flow from molecule to molecule in a solid substance.
Convection
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.
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 saving-to-investment ratio.
Cubic foot per minute (cfm) A measurement of air movement past a certain point or through a certain structure.
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D
Degree-days
A measure of the temperature element of climate produces by multiplying temperature difference by time.
Depressurize
Cause to have a lower pressure or vacuum with respect to a reference of a higher pressure.
Dew point
The warmest temperature of an object in an environment where water condensation from the surrounding air would form on that object.
Distribution system
A system of pipes or ducts used to distribute energy.
Duct Blaster
A blower-door-like device used for testing duct leakiness and air flow.
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E
Energy
A quantity of heat or work.
Energy consumption
The conversion or transformation of potential energy into kinetic energy for heat, light, electricity, etc.
Energy efficiency
Term describing how efficiently a building component uses energy.
Energy efficiency ratio (EER)
A measurement of energy efficiency for air conditioners. The EER is computed by dividing cooling capacity, measured in British Thermal Units per hour (Btuh), by the watts of power.
Energy factor
The fraction of water heater input remaining in an assumed 64 gallons of hot water used by residents.
Energy-recovery ventilator
A ventilator that recovers latent and sensible energy from the exhaust airstream and imparts it to the incoming airstream.
Envelope
The building shell. The exterior walls, floor; and roof assembly of a building.
Environmentally sensitive
A person who is highly sensitive to pollutants, often because of overexposure, is said to be environmentally sensitive.
Evaporation
The change that occurs when a liquid becomes a gas. Evaporation is the key process in the operation of air conditioners and evaporative coolers.
Evaporator
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.
Exfiltration
Air flowing out of a residence from its conditioned space through the shell.
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F
Fiberglass
A fibrous material made by spinning molten glass.
Fire stop
Framing member designed to stop the spread of fire within a wall cavity.
Flue
A channel within an appliance or chimney for combustion gases.
Foamboard
Plastic foam insulation manufactured most commonly in 4'x8' sheets in thickness of 1/4" to 3".
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H
Heat gains
Heat that accumulates in homes; this is desirable during the heating season and undesirable during the cooling season.
Heat loss
The amount of heat escaping through the building shell during some period of time like a month or a year.
Heat-recovery ventilator
A central ventilator that transfer heat from exhaust to intake air.
Heating load
The maximum heating rate needed by a building during the very coldest weather.
Heating seasonal performance factor (HSPF)
Rating for heat pumps describing how many Btus they provide per watt-hour of electricity consumed.
House pressure
The difference in pressure between the indoors and outdoors measured by a manometer.
Humidistat
An Automatic control that switches a fan, humidifier, or dehumidifier on and off to control relative humidity.
Hydronic
A heating system using hot water or steam as the heat-transfer fluid.
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I
Incandescent lamp
The common light bulb found in residential lamps and light fixtures and sold in stores everywhere.
Infiltration
The inflow of outdoor air into the indoors, which is accompanied by an equal outflow of air from indoors to the outdoors.
Insulated glass
Two or more glass panes spaced apart and sealed in a factory.
Insulation
A material that is designed to slow down the flow of heat in or out of a house.
Internal gains
The heat generated by bathing, cooking, and operating appliances, that must be removed during the summer to promote comfort.
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K
Kilowatt (kW)
A unit of electric power equal to 1000 joules per second or 3412 Btus per hour.
Kilowatt-hour (kWh)
A unit of electric energy equal to 3600 kilojoules or 3412 btus.
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L
Latent heat
The heat absorbed or released by a substance when it changes state. for instance, from a liquid to a gas.
Low-e
Short for low emissivity, which means the characteristic of a metallic glass coating to resist the flow of radiant heat.
M
Make-up air
Air supplied to a space to replace exhausted air.
Mastic
A thick creamy substance used to seal seams and cracks in building materials.
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O
Open-combustion heater
A heater that takes its combustion air from the surrounding room.
P
Pascal
A unit of measurement of air pressure.
Payback period
The number of years that an investment in energy conservation will take to repay its cost in energy savings.
Perm
A measurement of how much water vapor a material will let pass through it per unit of time.
Plate
A piece of lumber installed horizontally to which the vertical studs in a wall frame are attached.
Plenum
The piece of ductwork that connects the air handler to the main supply duct.
Polyethylene
Polymer plastic used for vapor barriers, air barriers, and foam backer rod.
Pressure
A force encouraging flow by virtue of a difference in some condition between two areas.
Pressure boundary
An air barrier - usually the primary air barrier.
Pressure diagnostics
The practice of measuring air pressures and flows in buildings.
Pressure pan
A device used to block a duct register, while measuring the static pressure behind it, during a blower door test.
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R
R-value
A measurement of thermal resistance.
Radiant barrier
A foil sheet or coating designed to reflect heat rays or retard their emission.
Radiant temperature
The average temperature of objects in a home like walls, ceiling, floor, furniture, and other objects.
Radiation
Heat energy, which originates on a hot body like the sun, and travels from place to place through the air.
Radon
A radioactive gas that decomposes into radioactive particles.
Recovery efficiency
A water heater's efficiency at actually heating incoming water.
Refrigerant
A special fluid used in air conditioners and heat pumps that heats air when it condenses and cools air when it evaporates.
Register
A grille covering a duct outlet.
Relative humidity
The percent of moisture absorbed in the air compared to the maximum amount possible. Air that is saturated has 100% relative humidity.
Resistance
The property of a material resisting the flow of electrical energy or heat energy.
Retrofit
An energy conservation measure that is applied to an existing building. Also means the action of improving the thermal performance or maintenance of a building.
Return air
Air circulating back to the furnace from the house, to be heated by the furnace and supplied to the rooms.
Rim joist
The outermost joist around the perimeter of the floor framing.
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S
Savings-to-investment ratio (SIR)
Measures how many times an energy retrofit pays itself during its lifetime.
Sealed-combustion heater
A heater that draws combustion air from outdoors and has a sealed exhaust system.
Seasonal energy efficiency ratio (SEER)
A measurement of energy efficiency for central air conditioners. The SEER is computer by dividing cooling capacity, measured in Btuh, by the watts.
Sensible heat
The heat absorbed by a substance which raises its temperature.
Sheathing
A structural sheeting, attached on top of the framing, underneath siding and roofing of a building.
Shell
The building's exterior envelope - walls, floor, and roof of a building.
Soffit
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 and contributes to the need for cooling.
Solar heat
Radiant energy from the sun with wavelengths between 0.7 and 1 micrmeters.
Solar heat-gain coefficient (SHGC)
The ratio of solar heat gain through a window to incident solar heat. Includes both transmitted heat and absorbed and reradiated heat.
Spillage
Temporary flow of combustion gases from a dilution device.
Split-system air conditioner
An air conditioner that has the condense and compressor outdoors and the evaporator indoors.
Supply air
Air that has been heated or cooled and is then moved through the ducts and out the supply registers of a home.
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T
Therm
A unit of energy equaling 100,000 Btus or 29.3 kilowatt-hours. Ten therms equal one decatherm (dkt).
Thermal break
A piece of relatively low conducting material between two high conducting materials.
Thermal resistance
Same as R-value, expressing ability to retard heat flow.
U
U-value
The amount of heat that will flow through a square foot of building cross-section with multiple slabs of materials, Also known as U-factor when applied to windows.
Unconditioned space
An area within the building envelope that is not intentionally heated or cooled.
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V
Vabor retarder
A material that retards the passage of water vapor.
Ventilation
The movement of air through an area for the purpose of removing moisture, air pollution, or unwanted heat.
Venting
The removal of combustion gases by a chimney or other type of combustion vent.
Visible transmittance
The percent of visible light transmitted by a glass assembly.
Volt
The energy contained in each unit of charge in joules per coulomb.
W
Watt
A unit of electrical power equivalent to one joule per second or 3.4 Btuh.
Weatherization
The process of reducing energy consumption and increasing comfort in buildings by improving energy efficiency of the building.
Weatherstripping
Flexible gaskets, often mounted in rigid metal strips, for limiting air leakage.
Window films
Plastic films, coated with a metallized reflective surface, that are adhered to window glass to reflect heat rays from the sun.
Worst-case depressurization test
A safety test, performed by specific procedures, designed to asses the probability of chimney backdrafting.
Z
Zone
A room or portion of a building separated from other rooms by an air barrier - not usually an effective air barrier.
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