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HVAC Glossary

Our goal is to provide you with the information needed to help choose the best HVAC equipment for your home. As you browse our website, reference this glossary for definitions of the most common HVAC industry words, phrases, and acronyms.



Annual Fuel Utilization Efficiency (AFUE), is a standardized measure of efficiency for furnaces and boilers.

Advanced Reciprocating Compressor

Type of compressor that uses a more efficient process for compressing refrigerant for better cooling efficiency.

Air Handler

An air handler is another term for a fan coil, which is typically installed with a heat pump as the indoor unit of a heating and cooling system. It controls your home environment by moving air over the coil, heating or cooling it, then sending it throughout ductwork in your home.

Air Purifier

Air purifiers help clean the air flowing through your HVAC system before it circulates, removing particulates, bacteria, and select viruses from the air that flows through the filter.



British Thermal Unit. Used for both heating and cooling, BTU is a measure of the heat given off when fuel is combusted. Or for cooling, it's a measure of heat extracted from your home. (One BTU is approximately equal to the heat given off by a wooden kitchen match.)


A British Thermal Unit (BTU) is the unit of heat required to raise one pound of water by one degree Fahrenheit. British Thermal Units per Hour (BTUH) is the benchmark used to display the capacity of heating systems, such as gas furnaces. Heat extracted by an air conditioner is measured in BTUs, while cooling and heating capacities are measured in BTUH.



Cubic Feet per Minute. A measurement of airflow that indicates how many cubic feet of air pass by a stationary point in one minute. The higher the number, the more air is being forced through the system.


The ability of a heating or cooling system to heat or cool a given amount of space. For heating, this is usually expressed in BTUs. For cooling, it is usually given in tonage.

Carbon Monoxide

A colorless and odorless, yet highly poisonous gas produced when carbon-based fuels burn. This includes natural gas, propane and more.

Carbon Monoxide Alarm

A device that reads and detects levels of carbon monoxide (CO) in your home. When unsafe levels of CO are present, a loud, high-pitched alarm will sound to alert you.

Central Air

Central air-conditioning offers comfort for your whole home. Air is cooled at a central location and distributed throughout your home via a fan and ductwork, as opposed to a window unit, which focuses on a certain room.


Part of the heat pump or air conditioner unit that controls the pressure applied to the refrigerant, necessary for taking in heat to warm your home or getting rid of heat to cool it.

Condenser Coil

Also referred to as an outdoor coil, this is part of the outdoor portion of a split-system air conditioner or heat pump. By converting refrigerant in a gas form back to a liquid, the coil sends heat carried by the refrigerant outdoors.


An HVAC condenser is another term used to describe either an air conditioner or heat pump



Decibels (dB) are a unit measuring the intensity of noise.


A damper HVAC,also known as a duct damper, is a type of valve found in ductwork that opens and closes to regulate airflow and direct it to certain areas of the home. Dampers are used in zoning or zone control systems.


A device that can be added to your heating and cooling system that works to draw excess moisture out of indoor air.


A type of furnace that takes cool air from the top and blows warm air to the bottom, if . located in a second-floor closet or utility area.

Dual Fuel Heat System

A dual fuel heat system combines the installation of a heat pump with your furnace, giving you two sources to heat your home. The heat pump is primary and the gas furnace kicks in during colder weather if the heat pump can’t meet the heating demands of your home.


Ductwork is a system of ducts, used to transfer warm or cool air from the furnace or air handler to the air vents throughout your home.


Energy Efficiency Ratio 2 (EER2)

Energy Efficiency Ratio 2 (EER2), is the cooling capacity of an air conditioner or heat pump unit for a specific amount of energy used in a specific testing climate. This standardized rating is important to know because it helps allow you to compare the efficiency of different cooling products.

Electronic Air Cleaner (EAC)

An Electronic Air Cleaner (EAC) is a device that utilizes electrically charged filters to reduce harmful contaminants such as viruses, bacteria, and allergens in indoor air. Electrically charged filters trap and kill harmful particles to prevent them from recirculating through your home.

Electronic Air Filter

The electronic air filter can be installed with your heating and cooling systems ductwork to help provide whole-home filtration.


ENERGY STAR is a U.S. government-backed program helping businesses and individuals protect the environment through superior energy efficiency. Products that are ENERGY STAR certified are both efficient and can help save on energy bills.

Evaporator Coil

An evaporator coil, also referred to as cooling coil or an indoor coil, is installed with your furnace and helps complete your air conditioner or heat pump system. Its purpose is to cool and dehumidify the air by converting liquid refrigerant into a gas, which absorbs heat from the air.


Fan Coil

A fan coil is an indoor unit of a heating and cooling system that controls your home environment by moving air over the coil, heating or cooling it, then sending it to ductwork throughout your home.


The trade name Freon is a registered trademark for R22 refrigerant belonging to The Chemours Company. Production of Freon ceased in 2015 per the Montreal Protocol.


Geothermal Heat Pump

Carrier geothermal heat pumps tap into the earth’s surface to use the energy and consistent heat found in the ground, instead of using outdoor air like traditional heat pumps.



Heating Seasonal Performance Factor 2 (HSPF2) is a standardized rating used by all heat pump manufacturers to compare energy efficiencies between split-system air-source heat pumps. Like miles per gallon for a car, the higher the HSPF 2, the more efficient the system.


Term used for Heating Ventilation and Air Conditioning.

Heat Exchanger

The part of a furnace that transfers heat to nearby air. That air is then distributed throughout the ductwork in your home.

Heat Pump

A heating and air conditioning unit that heats or cools by moving heat.

Horizontal Flow

A type of furnace, installed on its "side," that draws in air from one side, heats it and sends the warm air out the other side. Most often used for installations in attics or crawl spaces.


An HVAC humidifier can be added to an HVAC system to help improve indoor air quality.It’s typically installed in the ductwork of your system to help provide whole-home humidification.


A humidistat is a part of your heating and cooling system that senses the moisture level in the air and automatically adjusts it to maintain a set humidity level.

Hybrid Heat®

Hybrid Heat systems are a dual fuel systems that utilizes both an electric heat pump and a furnace. This system allows you to heat your home with the most energy-efficient option depending on the outdoor conditions.



Indoor Air Quality (IAQ) refers to the cleanliness of the air in a home. IAQ factors include particulate count (pollen, mold), humidity, and volatile organic compounds (VOCs) found in a home’s air – all of which can aggravate allergy and asthma symptoms.


Load Calculation

A series of studies performed to determine the heating or cooling requirements of your home. An energy load analysis uses information such as the square footage of your home, window or door areas, insulation quality, and local climate to determine the heating and cooling capacity needed by your furnace, heat pump, or air conditioner. When referring to heating, this is often known as a Heat Loss Analysis, since a home's heating requirements are determined by the amount of heat lost through the roof, entryways, and walls.

Low Boy

Low Boy is a type of furnace configuration in which the furnace is lower in height and occupies more floor space.



The Minimum Efficiency Reporting Value (MERV) is the standard comparison of an air filters efficiency. The MERV scale ranges from 1 (least efficient) to 16 (most efficient), and measures a filter's ability to remove particles from 3 to 10 microns in size.

Matched System

A heating and cooling system comprised of products certified to perform at promised comfort and efficiency levels when used together according to design and engineering specifications.


A multi-direction configuration that allows for both upflow and downflow installations.


Operating Cost

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


Packaged Product

Contrary to a split system, which has both an indoor and outdoor unit, a packaged product is an outdoor unit that contains all the components of the system in a single unit.

Payback Analysis

Overall measure of the efficiency and value of your home comfort system. By combining your purchase price and ongoing operating costs, a payback analysis determines the number of years required before monthly energy savings offset the purchase price.

Puron® Refrigerant

Puron Refrigerant is an environmentally sound refrigerant designed not to harm the earth's ozone layer. Puron Refrigerant is approved by the U.S. Environmental Protection Agency as a replacement for R-22.


R-22 Refrigerant

R-22, commonly known as Freon, is a single-component HCFC refrigerant with low ozone depletion potential. It has long been used in many air conditioning and refrigeration applications in a variety of markets. Production of R-22 ceased in 2015 per the Montreal Protocol.

R-410A Refrigerant

R-410A is a blend of refrigerants with low ozone depletion potential, commonly known as Puron. Production of R-410A will cease in 2024.

Reciprocating Compressor

A type of compressor used in air conditioners that compresses refrigerants by using a type of “piston” action.


Involves returning used refrigerant to the manufacturer for disposal or reuse.

Refrigerant Lines

Two copper lines that connect the Condenser (outdoor) Coil to the Evaporator (indoor) Coil.

Remote Access

Requires Wi-Fi® enabled model connected to a Wi-Fi network. Some models require a dedicated Wi-Fi router.

Remote Room Sensor

When the most convenient location for the main thermostat or control is not best for assessing the average conditions of the home (such as when it’s located near an exterior door), you can apply a remote sensor to feed information about the comfort conditions to the main unit.

Riello Burner

A burner assembly within your oil furnace that provides a cleaner, higher-quality combustion of heating oil to increase energy efficiency.



The seasonal energy efficiency ratio 2 (SEER2) is used to compare the energy efficiencies of different central air conditioners and heat pump systems. Like miles per gallon for a car, the higher the SEER2, the more efficient the system.

Scroll Compressor

A scroll compressor is a specially designed compressor that works in a circular motion instead of an up-and-down piston action. The scroll compressor is also known as scroll pump or scroll vacuum pump.

Setback 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.

Smart Recovery

Actively manages system ramp-up during “away” periods to meet homeowner comfort needs while saving money.

Smart Setback Programming

Uses information about indoor and outdoor conditions and the specifics of the system’s capabilities to determine the best temperature setback during “away” periods as well as when to ramp up to save energy while staying within homeowner min/max temperature preferences.

Split System

A split system is an HVAC system with both indoor and outdoor units, connected by tubing.

System Control

Thermostat, Infinity® system Control device used by homeowner to set temperature and other settings.



Device that monitors and controls your heating and cooling system.

Thermostatic Expansion Valve

A thermostatic expansion valve (TXV) is a precision device used to meter the flow of liquid refrigerant entering the evaporator at a rate that matches the amount of refrigerant being boiled off in the evaporator.


A unit of measure for cooling capacity. One ton = 12,000 BTUs per hour.



UL is an objective, nonprofit organization that tests, rates, and certifies electrical products for public safety.

UV Lamps

Ultraviolet (UV) lamps kill bacteria, mold, and mildew on your cooling coil in your HVAC system to help create a healthier indoor environment.


A type of furnace that draws cool air from the bottom and blows the warmed air out the top into the ductwork. This type of furnace is usually installed in a basement or an out-of-the-way closet.



Technology that allows your system to operate quietly and efficiently at longer, lower speed cycles throughout the day – meaning your system and comfort stay consistent.


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


Zoning System

An HVAC zoning system is a way to increase your home comfort and energy efficiency by controlling when and where heating and cooling occurs. Use a programmable thermostat and install dampers in the ductwork to direct airflow to certain “zones” of the home.

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