Quick Home Energy Check-up Glossary

The following glossary of terms may be useful to you as you review the results of your Quick Home Energy Check-up and recommendations for energy efficiency improvements. If you have any questions during the Check-up process, do not hesitate to ask your Check-up Professional.

AFUE: Annual Fuel Utilization Efficiency is a measure of the amount of heat actually delivered to your home compared to the amount of fuel that you must supply to the furnace.

Air Barrier: The barrier that prevents infiltration of outdoor air into the conditioned space and exfiltration of indoor air to the outside. Also known as “pressure boundary.” It should be continuous and aligned with the thermal boundary (the part of the home that physically separates the conditioned spaces from the unconditioned spaces).

Air Duct: A hollow conduit or 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 Leak: A hole, crack, or gap where air can leak into or out of a home. Air leaks can make a home feel drafty or uncomfortable and waste energy.

Air Sealing: The process of sealing bypass ducts in the pressure boundary to prevent air leakage. Air sealing reduces heat flow from air movement and prevents water vapor from entering the wall.

Attic Bypass: An air connection between the living space and the attic.

Baseload: The amount of energy (electric and natural gas or oil, if these are used for heating) used to operate lighting and appliances year-round. The minimum amount of energy your home uses.

Blower Door: A diagnostic tool used to test for air leakage.

CCF: Cubic foot; may be used as a measurement of natural gas usage and roughly equivalent to 1 therm or 1,020 British thermal units (BTUs).

CO: Carbon monoxide; an odorless, tasteless, poisonous combustion byproduct that is lighter than air.

Compact Fluorescent Light Bulbs (CFLs): Redesigned lights for use in most conventional light fixtures. CFLs use about 75% less energy compared to standard (incandescent) bulbs.

Conditioned Space: Areas or zones within the house that are heated or cooled for comfort.

Consumption Analysis: An analysis of energy usage. This could be an in-depth review of month-to-month usage or a comparative analysis before and after work is completed.

Cooling Load: The amount of energy consumed to provide seasonal cooling.

Cost-Effectiveness: An indicator of how worthwhile an investment is.

Crawlspace: The space under a house, often used to distribute mechanical and electrical systems. It is usually unconditioned.

DHW: Domestic Hot Water system.

Distribution System: When used in the context of the Check-up or an energy audit, the system through which heated or cooled air is distributed throughout the house.

Draft: The movement of combustion byproducts through the flue and chimney and out of a building.

Duct Blaster: Duct leakage testing equipment.

EER: Energy Efficiency Ratio. This is a measure of how efficiently a cooling system operates. The higher the EER, the more efficient the air conditioner.

Efficient-Flow Aerators: Water aerator that restricts flow to approximately 1½ gallons/minute.

Efficient-Flow Showerhead: Restrictive showerhead that limits water flow to 1½ gallons/minute.

EPA: U.S. Environmental Protection Agency.

Exfiltration: Air leakage. Air leaving the building through the building envelope, caused by pressurization with reference to outside (replaced by an equal amount of air entering the building).

Heating Load: The number of BTUs per hour that must be added to provide indoor comfort. Heating load is based on worst-case Winter Design temperatures determined by local weather statistics.

Heating Degree Days: A value reflecting the amount of energy needed to heat a building. Annual Heating Degree Days (HDDs) are the total HDDs in a year based on 30-year averages for specific climate regions.

Infiltration: Air leakage caused by depressurization with respect to outside. The air that enters a structure through the envelope (replaced by an equal amount of air leaving the home).

Insulation: Any material that slows heat transfer.

Kilowatt Hour: 1,000 watts; 1 kWh = 3,414 BTUs.

Knee Wall: A short wall, usually about 3 to 4 feet high, in the attic of a home, anchored with plates between the attic floor joists and the roof joist. Sheathing can be attached to these walls to enclose an attic space. Commonly found in Cape-style homes.

Rate of Return: The percentage of savings from an energy investment accrued each year.

Relative Humidity: The percentage of moisture vapor present in the air, relative to the total amount of moisture the air could hold at a specific temperature/pressure, expressed as a percentage.

Rim Joist: The external frame for a floor platform of a house. Also called box sill.

R-Value: The measured resistance of a material to heat transfer.

Savings to Investment Ratio (SIR): The life-cycle savings of an energy improvement divided by the initial investment. (For every dollar invested in an energy improvement, how many dollars will be saved over the life of the improvement in today’s dollars?)

Seasonal Efficiency: Total system efficiency. Includes Annual Fuel Utilization Efficiency (AFUE) and distribution losses. Average efficiency over the course of a heating season.

SEER: Seasonal Energy Efficiency Ratio. This is a measure of the energy efficiency of the air conditioning system. SEER ratings permit consumers to compare operating costs of various cooling systems and products.

Simple Payback: The number of years it takes for annual savings from an energy improvement to equal the initial investment.

Therm: A unit of heat equal to 100,000 British thermal units.

Thermostat: Control for maintaining heat at a prescribed temperature.

Unconditioned Space: An area or zone in a building that is not intentionally conditioned.