Glossary of HVAC Terms

You’ll experience a lot of jargon involved in shopping for and maintaining air conditioners. You may be familiar with some of these terms, but others may confuse you if you are not an industry professional. We’re here to simplify things for you with our list of common terms and their definitions.


A-coil: An A-shaped coil, also known as an evaporator coil, inside an air conditioner or heat pump that absorbs the heat from the air in your home.

Accumulator: A metal canister installed in the suction line of an air conditioning unit to keep liquid out of the compressor.

Air balance: This refers to the distribution of air by an air conditioning unit. A good AC unit will distribute cold air evenly throughout every room in the home.

Air changes per hour: How often per hour your air conditioning unit and ventilation system replace all the air in your home.

Air Conditioner: A device that changes the temperature and quality of indoor air, and sometimes the humidity level.

Air diffuser: A component in HVAC systems that mixes conditioned air with room air and spreads the air around a given space to increase comfort. Air diffusers are normally located in the floor or ceiling and covered by a grille.

Air exchange rate: This measures how quickly your air conditioning unit and ventilation system replace your indoor air with outside and/or conditioned air.

Air flow: The free motion of air.

Air flow volume: This refers to the amount of air your air conditioner circulates throughout your home. It is typically measured in cubic feet per minute.

Air handler/air handling unit: A device inside your home that regulates and circulates air through the ductwork.

Air infiltration: The unintended passage of air in or out of your home.

Air passages: Spaces in your walls, floor, or ceiling through which air can leave your home.

All-in-one system: An all-in-one heating and cooling system that contains all the components within one unit that is stored outside, or on top of the home. Also known as a packaged unit.

Ambient air: Unconditioned outside air.



Blower: See Air handler/air handling unit.

British thermal unit (BTU): The amount of heat required to raise the temperature of 1 pound of water by 1 degree Fahrenheit. This is the measurement used to express how well an air conditioner extracts heat.

British thermal units per hour (BTUH): The number of BTUs of energy that can be produced or removed in an hour.

Building envelope: Everything that separates the interior of the building from the outside world, including walls, windows, and doors.



Capacity: How well an air conditioner can remove heat from a given area.

Celsius: A temperature scale in which the freezing point of water is 0 degrees and the boiling point of water is 100 degrees.

Charge: The amount of refrigerant in a closed air conditioning system at a given time, or the act of adding more refrigerant to an AC system.

Coil: Could refer to one of two coils in an air conditioner or heat pump: the evaporator coil and the condenser coil.

Compressor: The part of an air conditioning system that pressurizes the refrigerant and allows it to circulate through the coils.

Condensate pan: A pan located below the evaporator coil that collects condensation from the conditioned air.

Condenser/Condensing Unit: A unit that is typically placed outdoors that removes heat from the air conditioning system.

Condenser coil: The part of an air conditioner that condenses the refrigerant into a liquid and releases heat from the system.

Condenser fan: The fan in an air conditioner that cools and circulates air over the condenser coil.

Conditioned air: Air that has had the heat and humidity removed from it and has been released from an air conditioner into your home.

Conditioned space: The area that an air conditioner cools.

Constant air volume system: A type of HVAC system that is designed to provide constant air flow throughout the home.

Controller: The device that controls the air conditioner, for example a thermostat.

Crankcase heater: A small heater for compressors that prevents refrigerant from mixing with crankcase oil.

Cycling: The full process of an air conditioner, from turning on to processing air to turning off.



Damper: A valve or plate that regulates air flow through a duct or air diffuser.

Dehumidifier: A device that removes excess moisture from the air. It is not a part of an air conditioner.

Diffuser: See Air diffuser.

Drain pan: See Condensate pan.

Dry-charged unit: An air conditioning unit that is shipped and installed without any refrigerant, and is charged after installation.

Dual-duct system: An HVAC system that reaches specific temperatures by mixing air from two separate ducts — one providing heated air and one providing cooled air.

Duct fan: A fan placed inside a duct to increase air flow within the duct.

Duct: A section of tubing designed to allow heated or cooled air to travel throughout the home.

Ductwork: A passageway of tubing throughout an entire home that allows heated or cooled air to travel.



Energy efficiency ratio (EER): A measure of air conditioner efficiency that is the equivalent of the cooling output of an air conditioner divided by the total amount of electricity used.

Energy Star: A label from the Environmental Protection Agency indicating appliances, including air conditioners, that are energy-efficient beyond the government’s minimum standards.

Environmental Protection Agency (EPA): A U.S. government agency whose purpose is protecting the environment and human health.

Evaporator coil: An A-shaped coil inside an air conditioner or heat pump that absorbs heat from your indoor air.

Expansion valve: A valve that restricts the flow of refrigerant into the evaporator coil, allowing the refrigerant to expand into a gas.



Fahrenheit: A temperature scale in which the freezing point of water is 32 degrees and the boiling point of water is 212 degrees.

Flue: A vent that removes exhaust and combustion byproducts.

Freon: A stable, low-toxicity chlorofluorocarbon gas or liquid commonly used as a refrigerant.

Furnace: A heating system that works in conjunction with an air conditioner or heat pump.



Heat gain: The amount of temperature increase in your home or a given area from the sun or other sources, which your air conditioner must account for to maintain your desired temperature.

Heat loss: The amount of temperature decrease in a given area.

Heat pump: A unit intended for mild climates that can either heat or cool indoor air, depending on the season.

Heat register: See Air diffuser.

Horizontal flow: An air handler installed on its side so that air circulates in one end and exhausts out the side. These are ideal for attics or crawl spaces.

Humidifier: A device that adds moisture to the air to increase humidity.

Humidistat: A device that measures humidity and controls a humidifier.

Humidity: The concentration of water vapor in the air.

HVAC: An acronym that stands for heating, ventilation, and air conditioning.



Indoor coil: See Evaporator coil.

Indoor/outdoor system: An air conditioning system where the compressor is kept outside the home and the evaporator coil is inside.



Load calculation: An analysis completed by an HVAC technician to determine which type of system is best for your home.



Matched system: An air conditioning system in which all parts are matched for size, capacity, and efficiency to ensure that it will run well and last a long time.

Minimum outside air: The lowest amount of fresh outdoor air allowed into an air conditioning system.



Outdoor coil: See Condenser.

Outdoor unit: See Condenser.



Packaged system: See All-in-one system.

Packaged unit: See All-in-one system.

Plenum space: An air compartment built into the home that is connected to the ductwork.

Programmable thermostat: A thermostat with the capability of adjusting the temperature inside your home on its own based on a program and settings that you choose beforehand.

PSI: Pounds per square inch, a measure of pressure.

PVC: Polyvinyl chloride, a type of plastic.



R-22 refrigerant: An outdated type of refrigerant that was the standard for many years but is now being phased out.

R-410A refrigerant: The current standard refrigerant that is free of chlorine and more environmentally friendly than previous types.

Reciprocating compressor: A compressor that works using a piston action as opposed to the more efficient circular motion of a scroll compressor.

Refrigerant charge: See Charge.

Refrigerant lines: Copper tubing that connects the condenser to the evaporator coil.

Refrigeration capacity: The measure of the cooling capability of an AC unit. This is measured in BTUs or tons.

Return air: Air from inside the home that comes back to the evaporator coil.

Return duct: Warm air is drawn through this duct and into the air conditioning system to be cooled down.

Rooftop unit: See All-in-one system.



Scroll compressor: A compressor that works in a circular motion. It typically operates more efficiently, more smoothly, and more quietly than reciprocating compressors.

Seasonal Energy Efficiency Ratio (SEER): The cooling output of an air conditioner divided by the total amount of electricity used during the same period. This is typically used to determine the efficiency of an AC unit.

Self-contained system: See All-in-one system.

Setback thermostat: See Programmable thermostat.

Single package: See Packaged unit.

Split system air conditioner: See Indoor/outdoor system.

Supply duct: The duct that blows conditioned air to different rooms in the home.



Temperature zones: Individual areas of a home in which the temperature can be controlled independently of other areas of the home.

Thermidistat: A device that monitors indoor temperature and humidity level, and automatically adjusts your air conditioner to maintain your desired indoor conditions.

Thermostat: A small device usually placed on a wall that controls the temperature inside your home.

Thermostatic expansion valve: A device that creates a constant evaporator temperature by regulating the flow of refrigerant through the system.

Ton: A unit of measurement for air conditioner capacity equal to 12,000 BTUs per hour.

Two-stage cooling: A cooling method with two operating levels: one with higher energy consumption for hotter days and one that uses less energy for milder days. This is generally a more efficient method.



Up-flow furnace: A furnace that pulls in air from the bottom and releases it through the top.



Variable speed motor: A fan motor that is used in a two-stage cooling system.

Vent: See Air diffuser.

Ventilation: The movement of air into and out of the home, naturally or mechanically.



Watt: A measure of electrical power.



Zone: See Temperature zone.

Zoning: A more efficient air conditioning system that divides the home into sections, such as different rooms or different floors.

Can’t Find What You’re Looking For in Our Glossary of HVAC Terms? Feel Free to Reach Out

ECM Air Conditioning, with its headquarters located in Boynton Beach, FL, provides air conditioning services within Palm Beach County, Broward County, Martin County, and St. Lucie County. If you’re having issues with your HVAC system, we’re on-call and ready to assist you with your air conditioning needs. So if you’re in need of an HVAC Contractor, don’t hesitate to contact us today to schedule an air conditioning service call diagnostic! Our HVAC experts will diagnose any issues that may be occurring with your HVAC system and help to repair your AC issue on the spot.

Best of all, because ECM is the largest HVAC company in South Florida our local warehouse facility that is 69,000 square foot houses over $1 million in inventory and fully stocks our 127 vehicles on the road, making us one of the very few AC service companies capable of repairing most issues right on the spot. That means no waiting and no downtime without air conditioning for you & your family in the blistering Florida heat!

Call us at 561-295-1763 or contact our HVAC team online.

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