Glossary of Terms
Acid Rain - Rain that has become acidic due to the
emission of sulfur dioxide and nitrogen oxides. To learn more,
see the U.S. Environmental Protection Agency's Acid Rain Home
Air Leakage Rating - The air leakage rating is a measure
of how much air leaks through the crack between the window
sash and frame. The rating reflects the leakage from a window
exposed to a 25-mile-per-hour wind, and is measured in cubic
feet per minute per linear foot of sash crack.
Annual Fuel Utilization Efficiency (AFUE) - A rating
that denotes the efficiency of gas heating equipment. It is
the amount of heating your equipment delivers for every dollar
spent on fuel. An indication of how well a furnace converts
energy into usable heat. A higher rating indicates more efficient
equipment. The rating is expressed as a percentage of the
annual output of heat to the annual energy input to the furnace.
This rating is calculated in accordance with the Department
of Energy test procedures.
Blower Doors - Energy contractors use blower doors
to see how much air leaks through windows, doors, and other
places in your house. The blower door is a large board that
blocks the front door of your house. A powerful fan installed
in the door draws the air out of your house and causes a strong
draft inside where ever the air is leaking in. This can help
the contractor locate the air leaks, and gives a good overall
indication of how "leaky" your house is.
British thermal unit (Btu) - One British thermal unit,
or Btu, is roughly equivalent to burning one kitchen match.
The standard of measurement used for measuring the amount
of heat required to raise the temperature of one pound of
water by one degree (Fahrenheit). That may not sound like
much, but a typical home consumes about 100 million Btus per
year. Approximately one-half for the total is used for space
Energy Efficiency Ratio (EER) - The ratio of the
cooling capacity of the air conditioner, in Btu per hour,
to the total electrical input in watts under test conditions
specified by the Air-Conditioning and Refrigeration Institute.
Global Warming - Global warming is the gradual increase
in global temperatures caused by the emission of gases that
trap the sun's heat in the Earth's atmosphere. Gases that
contribute to global warming include carbon dioxide, methane,
nitrous oxides, chlorofluorocarbons (CFCs), and halocarbons
(the replacements for CFCs). The carbon dioxide emissions
are primarily caused by the use of fossil fuels for energy.
Heat Exchanger - A device used to transfer hear from
a fluid (liquid or gas) to another fluid, where the two fluids
are physically separated (usually by metal tubing). Household
examples of heat exchangers are heating radiators and the
coils on your refrigerator and room air conditioner.
Heat Pump - Devices that extract available heat from
one area (the heat source) and transfers it to another (the
heat sink) to either heat or cool an interior space. For instance,
in heating climates, during the winter the heat pump extracts
heat from the air outside and transfers it to the inside of
the house to heat the house. In cooling climates, during the
summer the heat pump extracts heat from the air inside the
house, cooling it, and transfers it outside. Heat pumps work
very much like your refrigerator: heat is released from the
back of your refrigerator as it grows cooler inside. This
is exactly like cooling your house during the summer.
Heat pumps can be very energy efficient, because instead
of actually generating heat like a furnace, they just draw
heat from the outside. But because the efficiency drops as
the air outside gets very cold, many builders are turning
instead to ground-loop or geothermal heat pumps. These heat
pumps operate more efficiently than the standard air-source
heat pumps, because the ground doesn't get as cold as the
outside air (and during the summer, it doesn't heat up as
Heat Transfer - The flow of heat from one substance
to another, for instance, the flow of heat from your water
heating element to the water that surrounds it.
Heating Seasonal Performance Factor (HSPF) - The total
heating output of a heat pump in Btu during its normal usage
period for heating divided by the total electrical energy
input in watt-hours during the same period.
Housewrap - Housewrap is a sheet of plastic, often
fiber-reinforced, that is used to reduce air leakage in new
homes. These sheets are wrapped around the outside of a house
during construction. Builders must seal the housewrap at all
joints and seams to create a truly continuous, effective air
Infrared Cameras - Energy contractors use infrared
cameras to look at the heat leaking into or out of your house.
The infrared camera "sees" the heat and can show "hot spots"
where a lot of heat is being lost. This helps to identify
the places where your home's energy efficiency can be improved.
Kilowatt-Hour (kWh) One kilowatt-hour (kWh) is equal to using
1000 watts of electricity for one hour. This is equal to burning
a 50-watt light bulb for 20 hours, or roughly equivalent to
cooking a pot of rice for an hour. Your utility bill usually
shows what you are charged for the kilowatt-hours you use.
The average residential rate is 8.3 cents per kWh. A typical
U.S. household consumes about 10,000 kWh per year, costing
an average of $830 annually.
Seasonal Energy Efficiency Ratio (SEER) - The total
cooling output of a central air conditioner in British thermal
units during its normal usage period for cooling divided by
the total electrical energy input in watt-hours during the
same period. The test procedure is determined by the Air-Conditioning
and Refrigeration Institute.
Solar Heat Gain Coefficient (SHGC) - The solar heat
gain coefficient, also called a shading coefficient, is a
measure of how well a window absorbs or reflects heat from
the sun. The lower the coefficient, the better the window
is at blocking the sun's heat. Windows in hot or temperate
climates should have a low SHGC; south-facing windows in cold
climates should have a high SHGC.
Storm Windows - An extra pane of glass or plastic
added to a window to reduce air infiltration and boost the
insulation value of a window. If you are considering adding
storm windows, you should compare the costs to installing
new energy-efficient windows
Surface thermometers - As the name implies, surface
thermometers have a temperature probe that can be placed directly
on a surface to see what temperature it is. This can help
energy contractors evaluate how well heat is passing through
your doors, windows, walls, floor, and ceiling. Placed on
a window, for instance, it can tell you if the window is close
to the room temperature (indicating that it insulates well)
or closer to the outside temperature (indicating that it insulates
Vapor Barrier - Also called a vapor retarder, this
is a material that retards the movement of water vapor through
a building element (such as walls, floors, and ceilings) and
prevents metals from corroding and insulation and structural
wood from becoming damp.
Whole-House Fan - A large fan used to ventilate your
entire house. This is usually located in the highest ceiling
in the house, and vents to the attic or the outside. Although
whole-house fans are a good way to draw hot air from the house,
you must be careful to cover and insulate them during the
winter, when they often continue to draw hot air from people's