Glossary of Terms

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AFUE: Stands for Annual Fuel Utilization Efficiency and refers to the ration of annual output of useful energy or heat to the annual energy input to the furnace. The higher the AFUE, the more efficient the furnace – higher efficiency translates to more savings on fuel bills.

BALANCING: The process of adjusting the flow of air in duct systems, or water flow in hot-water heating systems. Proper balancing is performed using accurate instrumentation to deliver the right amount of heating or cooling to each area or room of the home.

BTU: Stands for British Thermal Unit and is the quantity of heat required to raise the temperature of 1 lb. of water 1 degree F at 39.2 degrees F. BTUH stands for British Thermal Unit Per Hour – this establishes a time reference to BTU input or output rates.

CENTRAL FORCED AIR HEATING SYSTEM: A piece of equipment that produces heat in a centralized area, then distributes it throughout the home through a duct system.

CONFIGURATION: This describes the direction in which a furnace outputs heat. A furnace may have an upflow, downflow or crossflow (horizontal) configuration.

DAMPER: A device that is located in ductwork to adjust air flow. There are basically two types of dampers; Manual, and motorized. A manual damper generally consists of a sleet metal (or similar material) flap, shaped to fit inside of a round or rectangular duct. By rotating a handle located outside of the duct a technician can adjust (see Balancing) air flow to match the needs of a particular area or room. A motorized damper is generally used in a zoned system (see Zoning) to automatically deliver conditioned air to specific rooms or zones.

DUCTWORK: The delivery system through which warm air from the furnace is brought to where it?s needed. Ductwork is made of sheet metal, fiberglass, or flexible plastic, and can be round or rectangular is shape.

EFFICIENCY: The rate at which a furnace maximizes fuel use. This rate is numerically described as a ratio called AFUE (see above). As of January 1991, no furnaces can be manufactured with efficiencies lower than 78% AFUE. High efficiency furnaces will be rates 85-95% AFUE.

ENERGY RECOVERY VENTILLATORS (ERV): These devices preheat incoming outside air during the winter and pre-cool incoming air during the summer to reduce the impact of heating and/or cooling the indoor air. This means that smaller capacity heating and cooling systems can be used in homes, which results in lower installation costs, lower peak demand for energy, and lower operating costs.

FORCED AIR: This describes a type of heating system that uses a blower motor to move air through the furnace and into the ductwork.

HEAT EXCHANGERS: These are devices that enable furnaces to transfer heat from combustion safely into breathable air. The primary heat exchanger transfers heat from combustion gases to the air blowing through the ductwork. It?s vital that none of the combustion gas itself gets into the air stream. The primary heat exchanger handles the hottest gases. In high-efficiency furnaces, secondary heat exchangers recover heat that used to be vented up the chimney with the exhaust gases. By recovering this heat, the furnace becomes more efficient. Part of the heat recovered here causes the water and acid to condense out the exhaust gas. Because this liquid is corrosive, secondary heat exchangers must be designed to prevent deterioration. Usually this means they are made of stainless steel or some derivative of it.

HEAT RECOVERY VENTILLATORS: These devices bring fresh, outside air into the home while simultaneously exhausting stale indoor air outside. In the process of doing this, HRVS remove heat from the exhaust air and transfer it to incoming air, pre-heating it. This allows for the reclamation of much of the energy that otherwise would simply be vented outside. The end result: home comfort systems operate more efficiently.

SIZING: Refers to the procedure a heating contractor goes through to determine how large a furnace (measured in BTUH) is needed to heat a house efficiently. Too small a furnace won?t deliver enough heating; too large a furnace increases energy costs and can have an adverse effect on comfort. Sizing depends on the square footage of the home, the amount of ceiling and wall installation, the window area, use of storm doors, storm windows, and more.

THERM: Another measurement of heat. One therm = 100,000 BTUH.

ZONING: A system in which living areas are divided into separate spaces and each space?s heating/air conditioning is controlled independently. This can be accomplished by using either multiple independent systems, or a single system using electronic controls and motorized dampers (see Damper).