HVAC Glossary


AFUE (Annual Fuel Utilization Efficiency): 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. A higher rating indicates more efficient equipment. This rating is calculated in accordance with test procedures outlined by the Department of Energy.

Air Handler: The evaporator section of an air conditioning system that circulates and delivers the conditioned air. The air handler is often referred to as the indoor unit. It contains the evaporator coil, indoor fan motor and generally a heat strip for supplemental heating.

Air Infiltration: Leakage of air into rooms through cracks, windows, doors and other openings.

Air Change: The amount of air required to completely replace the air in a room or building; not to be confused with re-circulated air.

Air Conditioner: Assembly of equipment for the simultaneous control of air temperature, relative humidity, purity, and motion.

Air Diffuser: Air distribution outlet or grille designed to direct airflow into desired patterns.

Air Flow: The distribution or movement of air.

Air Handler: The portion of the central air conditioning or heat pump system that moves heated or cooled air throughout a home’s ductwork. In some systems a furnace handles this function.

ARI (Air-Conditioning and Refrigeration Institute): A non-profit organization comprised of heating, air conditioning and refrigeration manufacturers. ARI publishes standards for testing and rating heat pumps and air conditioners to provide a standardized measure of comparison. Recently merged with the Gas Appliance Manufacturers Association (GAMA) to form the Air-Conditioning, Heating, and Refrigeration Institute (AHRI)

Balance Point: An outdoor temperature, usually between 30° F and 45° F, at which a heat pump’s output exactly equals the heating needs of the home. Below the balance point, supplementary electric resistance heat is needed to maintain indoor comfort.

Blower: An air handling device for moving air in a ductwork distribution system. Also called a fan.

BTU (British Thermal Unit): 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).

BTU/hr: The abbreviation for British thermal units per hour.

Capacity: The ability of a heating or cooling system to heat or cool a given amount of space. For heating, this is usually expressed in BTU’s. For cooling, it is usually given in tons.

Carbon Monoxide: Carbon Monoxide (CO) is a colorless, odorless gas produced by burning any fuel. CO is poisonous and symptoms of CO poisoning are similar to those of the flu: headaches, fatigue, shortness of breath, nausea and dizziness. The Consumer Product Safety Commission (CPSC) recommends a yearly, professional inspection.

CFM (Cubic Feet per Minute): The abbreviation for cubic feet per minute; commonly used to measure the rate of air flow in an air conditioning system.

Charge: Amount of refrigerant in a system.

Compressor: A machine that increases the pressure of gaseous refrigerant.

Condensation: The process by which a gas is changed into a liquid at constant temperature by heat removal.

Condensation Point: The temperature at which the removal of any heat will begin a change of state from a vapor to a liquid.

Condenser Coil: A series or network of tubes filled with refrigerant, located in the condensing unit that removes heat from the hot, gaseous refrigerant so that the refrigerant becomes liquid again.

Condensing Unit: The outside section of a an air conditioning system which pumps vaporized refrigerant from the evaporator, compresses it, liquefies it in the condenser and returns it to the evaporator coil. The outdoor portion of a split system air conditioner contains the compressor and outdoor coil.

Cooling Load: Heat which flows into a space from outdoors and/or indoors.

Damper: A type of “valve” used in ductwork that opens or closes to control airflow. Used in zoning to control the amount of warm or cold air entering certain areas of the ductwork distribution 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.

Direct Vent: Venting system for a gas heating unit. This type of unit brings in outside air for combustion and vents combustion gases directly outside through dedicated vent piping.

Down flow Furnace: A furnace that pulls in return air from the top and expels warm air at the bottom. Houses built on concrete slabs or crawl spaces often have this type of furnace.

Ductwork: 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 such as a furnace.

Efficiency A rating on home comfort equipment is that is similar to the miles per gallon rating on your car. The higher the rating number, the more efficient the system and the lower your fuel consumption will be.

Electronic Air Cleaner: An electronic device that filters out large particles and contaminants in indoor air. It then electronically pulls out tiny particles that have been electrically charged, such as viruses and bacteria, drawing them to a collector plate.

Emergency Heat (Supplemental or Auxiliary Heat): The back-up heat built into a heat pump system.

Energy Efficiency Ratio (EER): Means the ratio of the cooling capacity of the air conditioner in British Thermal Units per hour, to the total electrical input in watts under specified test conditions.

Evaporator Coil: Part of an air conditioner located indoors. The evaporator coil cools and dehumidifies the air by converting liquid refrigerant into a gas, which absorbs the heat from the air. The warmest refrigerant is then carried through a tube to the outdoor unit (condenser coil).

Filter: A device used to remove dust and other particles from air for the purposes of reducing the load on the respiratory system and to protect the HVAC equipment. Filters vary greatly in efficiency. Mechanical filters (fiberglass or pleated paper filters) use the MERV rating system to measure filter effectiveness. The higher the MERV rating, the better the filtration. MERV stands for Minimum Efficiency Reporting Value.

Freon®: The name commonly used for refrigerant. This is a brand name registered by DuPont. The correct name for this gas is R-22. It is a chlorofluorocarbon (CFC), and its use is strictly regulated by the Federal Government due to its effect on the ozone layer of the atmosphere. New products that use R-22 Freon are no longer allowed to be produced as of January 1, 2010.

Furnace: That part of a home comfort system which converts gas, oil, electricity or other fuel into heat for distribution within a home.

Geothermal or Ground Water-Source: Water from an underground well is being used as the heat source or heat sink for a heat pump.

Heat Exchanger: A device for the transfer of heat energy from the source to the conveying medium. In a gas furnace, the heat exchanger cells separate the combustion gasses from the air in the home that is being heated.

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.

Heating Capacity: The rate at which a specific device can add substantial heat to a substance, expressed in BTU/h (British Thermal Units per hour).

Heat Pump: A heat pump is a reverse cycle air conditioner. When you run your air conditioner, your outdoor unit will be blowing hot air (removing heat from your home and sending it outside). When you run your heat pump, you reverse the flow of refrigerant and remove the heat from the atmosphere outside and blow it inside. When the temperature dips below 40 degrees outside, the electric heat strip switches on to provide supplemental heat. Dual fuel systems combine a gas furnace with a heat pump. This offers a significant savings as compared to an electric back up heat source.

Heating Seasonal Performance Factor (HSPF): This is the total heating output of a heat pump in British Thermal Units during its normal usage period for heating divided by the total electrical energy input in watt-hours during the same period.

Home Comfort System: System in which air is treated at a central location and carried to and from the rooms by one or more fans and a system of ducts.

Horizontal Furnace: A furnace that lies on its side, pulling in return air from one side and expelling warm air from the other.

HVAC: Heating, Ventilation, and Air Conditioning.

Humidification: The process of adding moisture to the air within a space.

Humidifier: A piece of equipment that adds water vapor to heated air as it moves out of the furnace. This adds moisture to the air to protect your furnishings and reduce static electricity.

Humidistat: A device designed to regulate humidity input by reacting to changes in the moisture content of the air.

Humidity: The amount of moisture in the air.

Indoor Coil: See Evaporator Coil

Infiltration: Air flow into a space usually through walls and leaks around doors and windows.

Insulation: Any material that slows down the transfer of heat.

Kilowatt (kW): Equal to 1,000 watts. Kilowatt-hour (kWh) – This is a common unit of electrical consumption measured by the total energy created by one kilowatt in one hour.

Load Calculation: A design tool used to determine the heat gain and heat loss in a building so that properly sized air conditioning and heating equipment may be installed. Manual J version 8 is the current standard.

Matched System: A heating and cooling system comprised of products that have been certified to perform at promised comfort and efficiency when used together, and used according to design and engineering specifications.

NATE (North American Technician Excellence): A certification for HVAC technicians. Only well trained technicians can pass the series of tests to obtain NATE certification.

Operating Cost: The day-to-day cost of running your home comfort equipment, based on daily energy use.

Packaged Unit: A self-contained heating and/or air conditioning system.

Programmable Thermostat: A state of the art electronic thermostat with a built in memory that can be programmed for different temperature settings at different times of the day.

Puron®: The Carrier Corporation registered trade name for refrigerant R410a. This refrigerant has replaced Freon® R-22 in new equipment manufactured after January 1, 2010. Refrigerant R410a does not harm the ozone layer.

Reclaiming: Returning used refrigerant to the manufacturer for disposal or reuse.

Recycling: Removing, cleaning and reusing refrigerant.

Refrigerant: Absorbs heat by a change of state (evaporation) from a liquid to a gas, and releases heat by a change of state (condenses) from a gas back to a liquid.

Refrigerant Lines: Also known as a line set. Set of two copper lines connecting the outdoor unit and the indoor unit. Refrigerant travels from the condenser to the indoor coil and back through these lines.

Register: Combination grille and damper assembly which is installed in the supply openings in the room.

Relative Humidity: The ratio of the amount of vapor contained in the air to the greatest amount the air could hold at that temperature. This is normally expressed as a percentage.

Return Air: Air drawn into a comfort system after having been circulated from the supply to a room.

SEER: Seasonal Energy Efficiency Ratio. This is the approximate efficiency of an air conditioning unit over a season in a given climate. In the past, a unit with a SEER rating of 8.00 was considered standard efficiency and a unit with a 13.00 SEER was considered high efficiency. Since January 1st, 2006, the minimum SEER required by the Department of Energy is 13.00 and 15.00+ SEER is considered high efficiency.

Set point: The temperature to which a thermostat is set for desired comfort level.

Split System: A central air conditioner consisting of two major components. The system usually consists of the condensing unit which contains the compressor, installed outside the building and an air handling unit installed within the building that contains the evaporator coil. This is the most common type of air conditioning system installed in a home.

Supplementary Heat: The auxiliary or emergency heat, usually electrical resistance heat, provided at temperatures below a heat pump’s balance point.

Thermidistat: Highly sophisticated programmable thermostat that senses the outdoor temperature, indoor air temperature, and indoor relative humidity. A microprocessor communicates with the heating and cooling equipment to determine the most efficient way to achieve perfect comfort. Can be used to turn the air conditioning system on to reduce humidity without a call for cooling.

Thermostat: A temperature control device that consists of a series of sensors and relays that monitors and controls the functions of a home comfort system.

Tonnage: The unit of measure used in air conditioning to describe the cooling capacity of a system. One ton of cooling is based on the amount of heat needed to melt one ton (2000 lbs.) of ice in a 24 hour period. One ton of cooling is equal to 12,000 Btu/hr.

Up flow furnace: A type of furnace in a home comfort system that discharges air into the conditioned space via a top-mounted discharge plenum or through an overhead duct system.

Ventilation: The process of supplying or removing air, by natural or mechanical means, to or from any space. Such air may or may not have been conditioned.

Ventilator: A ventilator captures heating or cooling energy from stale indoor air and transfers it to fresh incoming air.

Water Source: Water is being used as the heat source or heat sink for a heat pump. Sources of underground water are wells and sources of surface water are lakes, large ponds, and rivers. Also known as Geothermal

Watt: A unit of electrical power.

Zone System: A method of dividing the ductwork in a home into zones using motorized dampers. This will enable you to control the temperatures in each area.

Zoning: The practice of providing independent heating and/or cooling to different areas in a structure. Zoning typically utilizes a system controller, motorized zoning dampers which are controlled by a thermostat in each zone, and a bypass damper to regulate static pressure in the supply duct.