• AFUE (Annual Fuel Utilization Efficiency): 90% means 90 cents for every dollar goes to heat your home … 55% means 45 cents goes right up the chimney
  • Airflow: The distribution or movement of air.
  • Air Change: The amount of air required to completely replace the air in a room or building; not to be confused with recirculated air.
  • Air Diffuser: Air distribution outlet or grille designed to direct airflow into desired patterns.
  • Air Handler: Fan-blower, filter and housing parts of a system.
  • Add On Heat Pump: Installing a heat pump in conjunction with an existing fossil fuel furnace. The result is a dual fuel system.
  • Balance Point: The lowest outdoor temperature at which the refrigeration cycle of a heat pump will supply the heating requirements without the aid of a supplementary heat source.
  • Blower (Fan): An air handler device for moving air in a distribution system.
  • BTU (British Thermal Unit): Quantity of heat required to raise the temperature of one pound of water one degree Fahrenheit.
  • Charge: Amount of refrigerant placed in a refrigerating unit.
  • Comfort Zone: The range of temperatures, humidity and air velocities at which the greatest percentage of people feel comfortable.
  • Compressor: Pump of a refrigerating mechanism which draws a low pressure on cooling side of refrigerant cycle and squeezes or compresses the gas into the high pressure or condensing side of the cycle.
  • Condensing Unit: Part of refrigerating mechanism which pumps vaporized refrigerant from the evaporator, compresses it, liquefies it in the condenser and returns it to the refrigerant control. The outdoor portion of a split system air conditioner contains the compressor and outdoor coil ignoring the reverse cycle operation, also the outdoor in a heat pump system.
  • Dehumidification: The reduction of water vapor in air by cooling the air below the dew point; removal of water vapor from air by chemical means, refrigeration, etc.
  • Defrost Cycle: The process of removing ice or frost buildup from the outdoor coil during the heating season.
  • Duct: A pipe or closed conduit made of sheet metal, fiberglass board, or other suitable material used for conducting air to and from an air handling unit.
  • Emergency Heat (Supplementary Electric Heat): The backup electric heat bulit into a heat pump system. The same as an auxiliary heater, except it is used exclusively as the heat source when the heat pump needs repair.
  • Filter: A device for removing dust particles from air or unwanted elements from liquids.
  • Furnace: The part of an environmental system which converts gas, oil, electricity or other fuel into heat for distribution within structure.
  • Heat Gain: The amount of heat gained, measured in BTU’s, from a space to be conditioned, at the local summer outdoor design temperature and a specified indoor design condition.
  • Heat Loss: The amount of heat lost, measured in BTU’s from a space to be conditioned, at the local winter outdoor design temperature and a specified indoor design condition.
  • Heat Pump: Compression cycle system used to supply heat to a temperature controlled space. Same system can also remove heat from the same space.
  • HEPA is High Efficiency Particulate Arrestor
  • HSPF (Heating Seasonal Performance Factor): The total heating output of a heat pump during its normal annual usage period for heating divided by the total electric power input in watt-hours during the same period.
  • Humidifier: A device that adds moisture to warm air being circulated or directed into a space.
  • Humidistat: A device designed to regulate humidity input by reacting to changes in the moisture content of the air.
  • Infiltration: Air flow inward into a space through walls, leaks around doors and windows or through the building materials used in the structure.
  • Indoor Unit: This is usually located inside the house and contains the indoor coil, fan, motor, and filtering device, sometimes called the air handler.
  • Indoor Coil: Refrigerant containing portion of a fan coil unit similar to a car radiator, typically made of several rows of copper tubing with aluminum fins.
  • KWH (Kilo Watt Hour): ten 100 watt light bulbs burning for one hour
  • Outdoor Coil: Refrigerant containing portio of a fan coil unit similar to a car radiator, typically made of several rows of copper tubing with aluminum fins.
  • Refrigerant: Substance used in refrigerating mechanism. It absorbs heat in evaporator by change of state from a liquid to a gas, and releases its heat in a condenser as the substance returns from the gaseous state back to a liquid state.
  • Register: Combination grille and damper assembly covering an air opening or end of an air duct.
  • Return Air: Air drawn into a heating unit after having been circulated from the heater’s output supply to a room.
  • SEER (Seasonal Energy Efficiency Ratio): The total cooling of a central unitary air conditioner or unitary heat pump in BTU’s during its normal annual usage period for cooling divided by the total electric energy input in watt-hours during the same period.
  • Setpoint: The temperature to which a thermostat is set to result on a desired heated space temperature.
  • Split System: Refrigeration or air conditioning installation, which places condensing unit outside or away from evaporator. Also applicable to heat pump installations.
  • Thermostat: A tempature sensitive switch for controlling the operation of a heater of furnace.
  • THERM = 100,000 btu’s
  • TON (12,000 btu’s) the amount of heat it takes to melt a ton of ice in 24 hours