Glossary of Terms
The field of Heating, Ventilating & Air Conditioning, or HVAC, has its own technical language. In order to make it easier for you to understand the terms and acronyms we use, here are the most often used HVAC technical terms with their definitions. Feel free to ask us to help you understand any other technical words we use.
This is the new minimum efficiency standard (effective January 2006) for an air conditioner or heat pump. All new units must now meet this standard. Previously manufactured equipment may be used, sold, and installed. SEER is defined later.
The Air Conditioning Contractors of America, a national trade association that represents heating, ventilation, air conditioning, and refrigeration contractors.
Air Handling Unit
Equipment with a heating element and/or cooling coil and other components in a cabinet or casing used to distribute the air through the duct system.
Annual Fuel Utilization Efficiency: A measurement of the seasonal energy efficiency of gas heating equipment. It is the annual output energy of the equipment divided by its annual input energy, expressed in consistent units (i.e. Btu-out per Btu-in). AFUE includes any input energy required by the pilot light but does not include any electrical energy or fans or pumps.
Air-Conditioning and Refrigeration Institute, a non-profit, voluntary organization composed of heating, air conditioning and refrigeration manufacturers. ARI publishes standards for testing and rating heat pumps and air conditioners.
British Thermal Unit/per hour. One of the two (watts-hours is the other) standard units of measure ( IP System) for the amount of energy consumed by a process, the amount of energy transferred from one location to another, or the amount of embodied energy (such as the heat contents of fuels). Specifically, it is the amount of energy required to raise the temperature of one pound of water by one degree Fahrenheit. The term 'kbty' stands for "kiloBtu" or 1,000 Btu. The term of 'Mbtu' stands for "MegaBtu" or 1,000,000 Btu. One Btu/his equal to 0.293 watt-hours (Wh).
The rate at which the heating or cooling load can be satisfied by a given equipment system designed to heat or cool and dehumidify a conditioned space or heat service hot water. Heating and cooling capacity is normally given on equipment nameplates in units of Btu/h. The air conditioning industry often uses units of "tons" to refer to equipment capacity. One ton of capacity equals 12,000 Btu/h.
A reciprocating or rotary pump for raising the pressure of air or another gas; this may be a single-stage or multistage unit. Reciprocating Compressor: a machine that compresses gases, composed of one or several cylinders; each cylinder contains a piston that is moved by a crankshaft through a connecting rod. Rotary Compressor: a machine having a rotating member that directly compresses fluid in an enclosed housing; the fluid pressure rises as the volume of the closed space decreases.
Coefficient of Performance: A measurement of the instantaneous efficiency of heating or cooling equipment. It represents the steady-state rate of energy output of the equipment divided by the steady-state rate of energy input to the equipment, expressed in consistent units(i.e. watts-out per watts-in or Btu/h-out per Btu-in). Most vapor-compression heating and cooling equipment has COPs greater than unity, that means it delivers more heat energy than it consumes.
A heating or cooling element made of pipe or tubing, (usually with plates or fins) used to transfer heat or cooling from inside the home to outside.
The final step in installing a heating or air conditioning system. Every component is checked and tested for compliance with codes, ACCA manuals, manufacturer requirements, and occupant needs. After commissioning, the technician will provide documentation of testing, provide all equipment manuals, and show the homeowner how to operate the system.
Condenser (Heat Exchanger)
The outside unit of a heating or air conditioning system, here the refrigerant condenses from a gas to a liquid and hot or cold air from the building is released to the outside.
A device that removes excess moisture and latent heat from the air.
The U.S. Department of Energy, the federal agency that sets industry efficiency standards.
Conduits used to carry air. They can be round or rectangular, sheet metal or fiberglass or vinyl tubes. In air conditioning systems they carry air from the home to the air conditioning system or furnace and back to the home.
Energy Recovery Ventilator, a machine that draws fresh air into the home and exhausts stale air from the home. It uses a process to preheat or pre-cool (depending on the season) to reduce energy costs associated with conditioning the air.
A government supported branding used to identify energy efficient products. The branding was developed by the US Department of Energy and the US Environmental Protection Agency.
U.S. Environmental Protection Agency
A self-contained heating unit that is designed to deliver heated air to a home.
Gas Appliance Manufacturing Association is a national trade association serving the interests of manufacturers of gas, oil, and electric appliances and equipment, components and related products used in residential, commercial, and industrial applications.
1. The part of a furnace that transfers heat from burning fuel to the air used to heat your home.
2. A device, such as a condenser or evaporator, in which heat is added or removed in order to heat or cool your home.
A heat pump is a heat transfer machine, collecting heat from one area (where it is not wanted) and depositing it in another (where it is wanted). It can act as a heating or cooling device depending on the flow of the refrigerant.
Heat Recovery Venilator, a machine that brings fresh air into a home through a process that preheats the air so it has less impact on your utility bill.
Heating Season Performance Factor is the measurement of the seasonal efficiency of an electric heat pump using a standard heating load and outdoor climate profile over a standard heating season. It represents the total seasonal heating output in Btu divided by the total seasonal electric power input in watt-hours (Wh). The resultant value for HSPF has units of Btu/Wh.
A device for adding moisture to warm air for your home.
Heating, ventilating, and air conditioning
Is air that enters your home through holes, gaps, and cracks, (e.g., plumbing or electrical holes, the heating and air conditioning system, doors, and windows).
Indoor air quality
The energy that suspends moisture vapor in the air.
The quantity of heat that must be added to or removed from the building (or the hot water tank) to satisfy specific levels of service - in other words, to keep the space temperature or hot water temperature at a specified thermostat setting ( see also the definitions of energy and thermostat).
A mathematical determination of how much cooling and heating (BTUs) an HVAC system must deliver for occupant safety and comfort. It is based on a variety of factors: square footage, building orientation, number of occupants, size and placement of rooms, number and size of windows and doors, amount of insulation, number of floors, and climate.
An ACCA procedure covering the proper design, installation, maintenance, and repair of ductwork.
An ACCA procedure covering the method for calculating heating and cooling requirements (load calculation) for single-family detached homes and mobile homes.
An ACCA publication covering the design, installation, and commissioning of a residential HVAC system.
An air conditioner or heat pump system composed of equipment that has been certified by ARI to work together to deliver the specified heating and cooling capacity at the stated efficiency rating.
Is a natural by product of the fungi family that thrives when organic substances and water combine under certain circumstances. Mold reproduces via spores that can remain dormant, yet viable, for years. Many molds are beneficial. For example, they are the "bleu" in bleu cheese, and we use them to make wine, penicillin, and antibiotics. However, some molds can cause health problems.
North American Technician Excellence, the nonprofit organization that tests and certifies HVACR technicians.
Planned maintenance agreement, which provides regular maintenance of your HVACR system. Most ACCA member contractors offer PMAs, although they may use different names such as Maintenance Inspection Agreement, Planned Service Agreement, Energy Service Plan, etc.
A refrigerant containing chlorine used in air conditioning systems. The EPA has mandated that R-22 cannot be manufactured after 2010 because it has been linked to the depletion of the ozone layer and global warming. Most commonly referred to by its trademarked name, Freon.
The refrigerant that replaces R-22. It does not contain chlorine. New residential units use R-410A.
A fluid that absorbs heat at low temperatures and rejects heat at higher temperatures.
Refrigerant Charge (or, "charging the refrigerant")
The procedure an HVACR technician performs to ensure that the system has enough of the right kind refrigerant for peak operating performance.
Relative Humidity (RH)
The percent of moisture actually in the air compared to the maximum amount of moisture the air can hold at that temperature.
Return, Return Air, Return Side
The path the air takes to get to an air-handling unit or furnace so it can be cooled or heated. It is the "return" path. The return side should be "balanced" with the supply side to ensure proper air flow and comfort.
(Seasonal) Energy Efficiency Ratio: A measurement of the instantaneous energy efficiency of cooling equipment. It normally is used only for electric air conditioning equipment. EER is the steady-state rate of heat energy removal by the equipment in Btu/h divided by the steady-state rate of energy input to the equipment in watts. Thus, the resultant value for EER has units of Btu/Wh. The EER of a given system is always higher than the COP of that system by a factor equal to the number of Btu/h in a watt, or 3.413.
The temperature of the air. This type of heat is measured with a thermometer.
A two-component heating and cooling (heat pump) or cooling only (air conditioner) system. The condensing unit is installed outside, the air handling unit is installed inside (preferably in conditioned space). Refrigerant lines and wiring connect them together.
Supply or Supply Side
The part of an HVAC system that takes (supplies) the conditioned air from the air-handling unit or furnace to your home. The supply side should be "balanced" with the return side to ensure proper air flow and comfort.
A control device that measures the temperature of the air in a home or the water in a hot water tank and activates the heating or cooling equipment to cause the air or water temperature to remain at a pre-specified value, normally called the set point temperature (see also the definitions of load and energy).
A term used primarily by the air conditioning industry to characterize the cooling capacity of air conditioning equipment. One ton equals 12,000 Btu/h.
Ton of Refrigeration - The amount of heat necessary to completely melt one ton of 32 oF ice in 24 hours.
Zones, Zoned System, Zoning
A single HVAC system that can meet different heating and cooling needs in different areas (zones). Each zone of a home has its own thermostat with which it can regulate the temperature and humidity in its area. One "zoned air conditioner" could be set for a high temperature in one zone and for a lower temperature in the other zone. Zone systems have two or more zones.