AIR BARRIER – Any part of the building shell that offers resistance to air leakage.

AIR EXCHANGE – The total building air exchanged with the outdoors through air leakage and ventilation.

ANNUAL FUEL UTILIZATION EFFICIENCY (AFUE) – A laboratory derived efficiency rating for heating appliances that 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) – Measurement of energy, 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.

CELLULOSE INSULATION – Insulation made from recycled newspaper and cardboard treated with a fire retardant.

CFM 50 – 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. It is the most common and accurate way of comparing the air tightness of buildings that are tested with a blower door.

CFM N – The number of cubic feet of air flowing through a house during natural conditions.

COEFFICIENT OF PERFORMANCE – Rating of heat pump efficiency ranging from 1.5 to 4, the higher the better.

CONDENSE – When a gas turns into a liquid, opposite of evaporation.

CONDUCTION – Heat flow in a solid substance.

CONVECTION – Transfer of heat caused by the movement of a fluid like water or air.

DEGREE DAYS – A measure of the temperature element of climate in a certain location. The government lists the degree-days for different localities.

DEW POINT – The warmest temperature of an object in an environment where water condensation would form on that object.

ENVELOPE – The building shell generally consisting of exterior walls, floor, and roof assembly.

GABLE – The triangular section of an end wall formed by the pitch of the roof.

HEAT RECOVERY VENTILATOR- A central ventilator that transfers heat from exhaust to intake air.

HOME HEATING INDEX (HHI) -  The number of BTUs of energy used by a building divided by its area, and then divided by heating degree-days.

JOIST – A horizontal framing member that supports a floor or ceiling.

Kilowatt (KW) – Unit of electrical power.

MINIMUM VENTILATION GUIDELINE (MVG) – The measured blower door air leakage value below which mechanical ventilation is necessary.

PAYBACK PERIOD – The number of years that an investment will take to repay its cost.

PERM – A measurement of how much water vapor a material will let pass.

R – VALUE  - A measure of thermal resistance.

RADON – A radioactive gas.

RAFTER – A roof beam that follows the roof’s slope.

RELATIVE HUMIDITY – The percent of moisture absorbed in the air compared to the maximum amount possible.

RIM JOIST – The outermost joist around the perimeter of the floor framing.

SAVINGS TO INVESTMENT RATIO (SIR) – Measures how many times an improvement pays for itself during its lifetime.

SEALED COMBUSTION – A combustion appliance that draws combustion air from outdoors and has a sealed exhaust system. Requires no chimney.

SEASONAL ENERGY EFFICIENCY RATIO – A measurement of energy efficiency for central air conditioners, minimum of 8.9 rating.

SHADING COEFFICIENT (SC) – A decimal describing how much solar energy is transmitted through a window opening, compared to clear glass with an SC of 1.0.

SOFFIT – The underside of a roof overhang or a small lowered ceiling.

SPLIT SYSTEM – An air conditioner or heater that has the compressor outside and the active element inside.

STEADY STATE EFFICIENCY – The efficiency of a heating appliance measuring the heat that crosses the heat exchanger and is measured with a combustion analyzer.

THERMAL BARRIER – A material that protects materials behind it from reaching 250 degrees during a fire. Drywall is a 15-minute thermal barrier.

THERMAL BOUNDARY – A line or plane where insulation and air barriers exist in order to resist thermal transmission and air leakage.

U FACTOR – The amount of heat that will flow through a square foot of building cross section experiencing a temperature difference of 1 degree F.

UNCONDITIONED SPACE – An area within a building not intentionally heated or cooled.

VAPOR BARRIER – A material that retards the passage of water vapor.