Absolute humidity - Air moisture content expressed in grains (or pounds) of water vapor per pound of
dry air.
Absorptance - The ratio of a solar energy absorbed to incident solar. Also called absorptivity.
Absorption - A solid material's ability to draw in and hold liquid or gas.
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 conditioning - Cooling buildings with a refrigeration system. More generally means both heating and
cooling.
Air exchange - The total building air exchanged with the outdoors through air leakage and ventilation.
Air handler - A steel cabinet containing a blower with cooling and/or heating coils connected to ducts.
Asbestos - A material made of brittle mineral fibers that damage lungs and other bodily tissues.
Annual fuel utilization efficiency (AFUE) - A laboratory-derived efficiency rating for heating appliances
which accounts for chimney losses, jacket losses, and cycling losses.
Annual return - The yearly savings divided by the initial cost needed to achieve the savings, expressed as
a percent.
, Backdrafting - Continuous spillage of combustion gases from a combustion appliance.
Backdraft damper - A damper, installed near a fan, that allows air to flow in only one direction
British thermal unit (Btu) - The quantity of heat required to raise the temperature of one pound of water
one degree Fahrenheit.
Capillary action - The ability of water to move through materials, even upward against gravity, through
small tubes or spaces.
Carbon dioxide - One of two main products of complete combustion of a hydrocarbon(Do you recall the
other?)
Combustion efficiency - Synonymous with fuelburning efficiency or steady-state efficiency. Usually
means the latter.
Depressurize - Cause to have a lower pressure or vacuum with respect to a reference of a higher
pressure.
Distribution system - A system of pipes or ducts used to distribute energy.
Dormer - A vertical window projecting from a roof.
Draft diverter - A device located in gas appliance chimneys that moderates draft and diverts down drafts
that could extinguish the pilot or interfere with combustion.
Draft inducer - A fan that depressurizes the venting system and exhausts combustion products.
Drywall - Gypsum interior wallboard used to produce a smooth and level interior wall surface and to
resist fire. Also called sheetrock.
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