Industry Terminology

Industry Terminology

  • AFUE

    Annual Fuel Utilization Efficiency. The AFUE tells you what percentage of your energy dollar spent for fuel goes into your house, the rest goes up the stack. If you buy a furnace with an AFUE of 80, it means 20 cents out of every dollar in fuel goes up the stack.

  • AHRI

    The Air Conditioning, Heating, and Refrigeration Institute (AHRI) is a North American trade association that represents HVAC manufacturers, and tests equipment to ensure government standards are met.

  • AHRI Reference Number

    All HVAC equipment tested and certified by AHRI receives a unique reference number.

  • Air Cleaner

    An HVAC product designed to filter pollutants out of indoor air.

  • Air Handler

    The air handler is responsible for pushing conditioned air through ductwork or directly into an interior space.

  • Air-Side Economizer

    A controlled means by which an HVAC system introduces fresh air into a space to alleviate the need for artificial cooling in mild/cold weather conditions.

  • Airflow

    The amount of air an HVAC system can move in cubic feet per minute.

  • AOH

    Based on geographical factors and anticipated weather conditions, annual operating hours (AOH) estimate the number of hours an air conditioner, furnace, or other HVAC unit might typically operate in a year.


    ASHRAE is a global organization focused on sustainable, built environment technology. Formerly the American Society of Heating, Refrigeration, and Air Conditioning Engineers.

  • Boiler

    A boiler is a pressurized vessel used to generate steam for heating.

  • BTU

    BTU stands for British thermal unit, which is a unit of heat energy. One Btu is the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit.

  • BTU/H

    British Thermal Units per Hour (BTU/H) are a rate at which a system consumes or delivers units of heat energy in an hour.

  • Carbon Monoxide

    Often called the silent killer, carbon monoxide is an invisible, odorless, colorless gas created when fuels (such as gasoline, wood, coal, natural gas, propane and oil) burn with inadequate amounts of oxygen, creating a condition known as incomplete combustion.

  • CEER

    CEER stands for Combined Energy Efficiency Ratio and is most typically associated with room air conditioner or window air conditioner HVAC units. CEER measures the combined efficiency of the unit when it is in standby and when it's actually cooling a space.

  • Central Air Conditioning System

    System in which air is cooled at a central location and distributed to and from rooms by one or more fans and a series of ducts.

  • Certified Matched System

    A heating and cooling system comprised of equipment that has been certified to perform at certified efficiency levels when used together, and used according to design and engineering specifications.

  • CFC

    Chlorofluorocarbon (CFC) refrigerants are ozone-depleting chemicals once used as air conditioner and heat pump refrigerants.

  • CFM

    Cubic Feet per Minute indicates how many cubic feet of air passes by a stationary point in one minute. The higher the number, the more air that is being moved through the ductwork by the system.

  • Chiller

    Chiller systems remove heat from water in large-scale cooling applications.

  • Combustion

    Combustion takes place when gaseous, liquid or solid fuels react at an elevated temperature with oxygen by burning, thus releasing heat.

  • Compressor

    The outdoor portion of an air conditioner or heat pump that compresses and pumps refrigerant to meet household cooling requirements.

  • Condensate

    The liquid that separates from a gas due to a reduction in temperature or an increase in pressure.

  • Condenser Coil

    The outdoor portion of an air conditioner or heat pump that either releases or collects heat, depending on the time of the year.

  • Condensing Furnace

    This is a furnace with an AFUE of 89% or higher. Efficiency is achieved by extracting heat from the exhaust gases to the point where water is condensed out of the gases.

  • COP

    Coefficient of Performance (COP) is a metric for measuring performance efficiency. Higher COP is better than lower COP.

  • Damper

    When used in ductwork, the damper is a movable plate that regulates airflow. Dampers are used to direct air to the areas that need it most. Typically used in zoning applications.

  • dB

    A decibel (dB) is a unit used to measure the relative intensity of sound.

  • Defrost

    The defrost cycle on an HVAC system is used to melt accumulated ice.

  • DOE

    Abbreviation for the U.S. Department of Energy, the federal agency responsible for setting national appliance efficiency standards and monitoring the consumption of energy sources.

  • Downflow

    Usually installed in an attic, downflow HVAC units draw air in from the top of the cabinet and blow warm air out through the bottom.

  • Dry-Charged Unit

    A dry-charged unit is any air conditioner or heat pump system shipped from the factory without refrigerant pre-charged in the coils.

  • Dual Fuel

    A heat pump and furnace combination system that uses both electricity and gas to heat.

  • Ductwork

    The system by which air is channeled from the furnace or the blower coil throughout your home.

  • EER

    Energy Efficiency Ratio (EER) is a rating system used to measure the efficiency of an air conditioner. A higher EER is better.

  • Electric Heat Strip

    An electric heat strip looks like a series of coils. It attaches to the air handler on an air conditioning system and then heats the air coming out of the blower using radiant heat (with the AC in “fan only” mode). Essentially, it converts the air handler into a small-scale electric furnace.

  • Electronic Air Cleaner

    An electronic device that filters out large particles and bio-aerosols in indoor air.

  • Energy Factor

    Energy Factor (EF) is the amount of energy delivered as heated water in a day divided by the total daily energy consumption of a residential water heater. The EF is used to compare the energy efficiency of water heater models. Water heaters with higher EFs will have lower annual operating costs than comparable models with lower EFs.

  • Energy Guide Label

    A bright yellow tag indicating how much energy an appliance uses, and the estimated annual operating cost.

  • Energy Input Rating

    The amount of input energy delivered at the burner of furnaces, water heaters and boilers, measured in British thermal units (BTUs) per hour.

  • Energy Star

    An EPA designation attached to HVAC equipment to identify models that meet EPA guidelines for high-efficiency performance that exceed standard government minimums.

  • EPA

    An abbreviation for the U.S. Environmental Protection Agency, the federal agency that develops and enforces federal environmental regulations. The EPA oversees the nationwide ENERGY STAR® program.

  • Evaporator Coil

    The part of the air conditioner or heat pump that is located inside the air handler or attached to the furnace. Its primary function is to absorb the heat from the air in your house.

  • Fan Coil

    A fan coil consists of a fan and a coil. They are common in duct-free systems.

  • FHR

    First Hour Rating (FHR) is a measure of the capacity of a water heater referring to the amount of hot water a tank water heater can supply in an hour starting with a full tank of hot water. The number is stated in gallons and is found on the top left corner of the Energy Guide label.

  • Flow Rate

    The amount of water in gallons flowing past a fixed point over a period of time, typically expressed in gallons per minute.

  • FLUE

    The passageways in heating equipment and vents through which combustion products pass to the outside atmosphere.

  • FLUE Collar

    The portion of a gas appliance designed for the attachment of a venting system.

  • Flue Damper

    When a combustion heating system comes on, the flue damper automatically opens access to the flue, so that potentially damaging byproducts can be expelled safely.

  • Furnace

    A combustion heating system that will keep your home warm in cold weather.

  • FVIR Technology

    Flammable vapor ignition-resistance technology prevents the ignition of flammable vapors around your water heater. All gas-fired residential tank water heaters manufactured since July 1, 2003, must have this technology.

  • GAMA

    The GAMA Efficiency Rating Certified logo appears on space and water heating equipment that has been certified by the Air-Conditioning, Heating and Refrigeration Institute. It is your guarantee that the equipment’s energy-efficiency ratings have been independently verified by a third party. Space and water heating equipment displaying the GAMA emblem includes furnaces, water heaters, boilers and direct heating equipment.

  • Gas Furnace

    A combustion furnace fueled by natural gas.

  • Gas Pack

    An HVAC system that houses both cooling and gas heating components in the same cabinet.

  • Geothermal

    An energy efficient heat pump design that uses the Earth as its heat source and sink.

  • Heat Exchanger

    The heat exchanger is responsible for heating the air that is then distributed throughout the interior environment.

  • Heat Pump

    A heat pump is an air conditioner with a reversing valve that allows for the ability to provide heating in addition to cooling.

  • HEPA Filter

    A High Efficiency Particulate Absorption (HEPA) filter can remove pollen, dust, mold, and other particulate pollutants from indoor air.

  • Horizontal Flow

    A Horizontal Flow unit is a design that draws air into one side of a cabinet, then expels the air into ductwork or a conditioned space connected to the other side.

  • HSPF

    Heating Season Performance Factor (HSPF) is the metric used to measure the heating efficiency of heat pumps. The higher the HSPF rating, the better.

  • Humidifier

    A humidifier adds moisture to interior air.

  • Humidistat

    The humidistat is an HVAC tool that can automatically monitor and manage the humidity level in your home.

  • Humidity

    In an HVAC context, humidity is a measure of the moisture level in your home air.

  • HVAC

    Heating, Ventilating, and Air Conditioning (HVAC) systems are used to deliver effective air comfort in homes all over the world.

  • IAQ

    Indoor Air Quality (IAQ) is a term used to describe the state of your home air.

  • Kilowatt

    Kilowatt (kW) is a measure of electrical power equal to 1000 watts.

  • LEED

    Leadership in Energy and Environmental Design (LEED) is a program to certify buildings that are environmentally conscious in construction, design, and daily operation.

  • Lineset

    In a heating and air conditioning system, a lineset is the conduit for refrigerant to move between interior and exterior components.

  • Load Calculation

    A load calculation can be performed to determine a building's ideal HVAC system production capacity.

  • Louver

    A louver is a system of blades, sometimes adjustable, in a duct or frame to manipulate air movement.

  • Manual J Calculation

    The Manual J Calculation is a load calculation specifically for residential HVAC systems. If you don't know what size air conditioner you need for your home, a Manual J Calculation will tell you.

  • Media Filter

    A media filter is the component in an air cleaner that physically removes the pollutants from interior air.

  • MERV Rating

    Minimum Efficiency Reporting Value (MERV) is a measure of air filter effectiveness. The higher the MERV rating, the better the filter will trap foreign particulate.

  • Microchannel

    A microchannel coil is designed with small channels in the tubes to increase energy efficiency.

  • Net Metering

    Net metering is a service many utility companies provide to customers with solar panels. The solar power goes into the grid, and the homeowner may receive credit at full retail value.

  • Oil Furnace

    An oil furnace is a combustion heating system that uses oil for fuel.

  • Package Unit

    A package unit houses all the necessary heating and/or cooling components in a single cabinet.

  • Packaged Terminal Heat Pump

    A packaged terminal heat pump is similar to a through-the-wall PTAC, but utilizes a heat pump instead of only an air conditioner.

  • Pilot Light

    The pilot light on a combustion heating system is a small gas flame used to ignite the main burner.

  • Programmable Thermostat

    A programmable thermostat allows a homeowner to control and program their heating and air conditioning system.

  • Prop 65 WARNING

    This product can expose you to chemicals including lead and lead compounds, which are known to the State of California to cause cancer and birth defects or other reproductive harm. For more information go to

  • PSC Motor

    A permanent-split capacitor (PSC) motor is commonly used in HVAC blowers, fans, and air handling units.

  • PTAC

    A Packaged Terminal Air Conditioner (PTAC) is a self-contained air conditioning system installed through a wall, typically in an apartment or hotel.

  • PV Module

    Photovoltaic (PV) modules convert solar energy into electricity.

  • R-22 Refrigerant

    A previous generation chemical refrigerant used in HVAC systems that is slowly being phased out of active use.

  • R-410A Refrigerant

    A non-ozone depleting refrigerant used in HVAC systems and approved to replace previous generation chemicals like R-22.

  • Radiant Floor

    A radiant floor system circulates hot fluid via subfloor channels to deliver even, powerful heating.

  • Refrigerant

    Refrigerant is the chemical in an air conditioner coil that traps and moves heat throughout the system.

  • Room Air Conditioner

    Room air conditioners are compact, single-zone units designed for easy installation in a window or through the wall.

  • Rotary Compressor

    A rotary compressor uses a roller design to compress refrigerant in an HVAC system.

  • Scroll Compressor

    A scroll compressor uses a spiral design to compress refrigerant in an HVAC system.

  • SEER

    Seasonal Energy Efficiency Ratio (SEER) measures how efficiently an air conditioner or heat pump operates over a cooling season. Higher SEER is always better.

  • Single-Stage

    A single-stage operating system is the current industry standard in heat pump and air conditioner units.

  • Split System

    An HVAC split system requires linked interior and exterior components.

  • Thermal Efficiency

    The thermal efficiency of a water heater is a measure of how much heat it can generate from a given amount of energy.

  • Thermidistat

    A thermidistat automatically adjusts an HVAC system to maintain a desired interior humidity.

  • Thermostat

    A thermostat automatically adjusts an HVAC system to maintain the indoor temperature you desire.

  • Two-Stage Operation

    Two-stage operation provides superior efficiency and better long term performance than a single-stage system.

  • TXV

    A thermal expansion valve (TXV) measures the refrigerant flowing out of the evaporator and controls the refrigerant flowing into it.

  • Upflow

    Usually located in a basement or closet, upflow HVAC systems draw in air through the side or bottom and circulate it out through the top.


    The United States Green Building Council is a nonprofit organization dedicated to sustainability-focused practices in the building industry.

  • UV Light System

    Ultraviolet (UV) light systems neutralize and kill airborne pathogens.

  • Variable Speed

    Variable speed blower motors can manipulate airflow to improve comfort and efficiency.

  • Water Heater

    A water heater is a device that heats water for household use.

  • Zoning

    Zoning partitions a building into separate zones to maximize comfort and operational efficiency.

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