HVAC Glossary: Your Comprehensive Guide to Heating, Ventilation, and Air Conditioning Terms

Alright, let’s talk HVAC. And it’s more than just the AC coming on in the summer or the furnace blasting in the winter. HVAC—Heating, Ventilation, and Air Conditioning—is the cornerstone of indoor comfort. You likely are the same as me in this regard — you want to know what’s going on behind the scenes. This is not a game of one-upmanship, it’s about making an intelligent choice for the place you live and work. And that’s where this HVAC glossary comes to the rescue. We’re cutting through all those confusing terms and acronyms to make them as simple as possible, so you can finally understand what your HVAC guy is talking about.

Navigating the World of HVAC Terms: An A-Z Guide

Understanding HVAC terminology can feel like learning a new language. But don’t sweat it! Consider this your cheat sheet. Below, you’ll find a comprehensive list of HVAC terms, acronyms, and definitions, organized alphabetically to help you quickly find exactly what you’re looking for.

A

• Absolute Pressure: The pressure measured from a perfect vacuum, so 0 PSIA (pounds per square inch absolute) is equivalent to absolute zero pressure. Sometimes shown as “psia”.
• Accumulator: A vessel that stores liquid refrigerant to ensure that it does not flow into the compressor.
• AC (Alternating Current) A form of electrical current in which its direction changes periodically.
• AC Fans: Fans that utilize AC motors to generate air movement.
• AFUE (Annual Fuel Utilization Efficiency): A measure of how efficient a furnace is at converting fuel to heat. The higher the AFUE, the more efficient the furnace.
• AGA (American Gas Association, Inc.): An association involved in the gas industry.
• AHRI (Air Conditioning, Heating, and Refrigeration Institute): A trade organization that applies standards to HVAC equipment. By choosing equipment with the AHRI Certified mark, you can be confident it will perform.
• Air Changes Per Hour (ACH): The number of times the air in a space is replaced each hour.
• Air Conditioner: A cooling and dehumidifying unit.
• Air-cooled, air-cooled system: A system of air conditioning in which the heat is directly rejected to the outside air without use of a condenser water circuit.
• Air Handler: The indoor part of a system, which houses the blower, evaporator coil, and for some systems, a heating unit. Also called a coil blower.
• Airflow Volume: The quantity of air a HVAC system conveys, measured in cubic feet per minute (CFM).
• Air Purifier: An appliance that purifies air by removing pollutants. The finest purifiers are hardwired into the ductwork.
• ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers): A professional organization dedicated to advancing HVAC industry technology.
• AR Type Compressor: A compressor which is more efficient in compressing refrigerant.

B

• Balance Point: The outdoor temperature at which the output of a heat pump exactly equals the heating needs of the home.
• Bioaerosols: Airborne biological particles.
• Blend: Combination of more than one material.
• Boiler: An enclosed vessel in which liquid is heated to the point of vaporization.
• Brazing: A process by which metal parts are joined with the aid of a filler and heat.
• BTU (British Thermal Unit): A unit of heat value. A BTU is the amount of energy required to raise one pound of water by one degree Fahrenheit.
• BTUh (British Thermal Units per hour): A measure of heating or cooling output, over an hour.
• Bubble Point: – Liquid where first vapor bubble is formed.
• Burner: A source of flame that provides heat.
• Burner Orifice: Tiny hole that permits gas to enter the burner; a small orifice adjusts a small flame and larger orifice adjusts a large flame.

C

• Capacity: The amount of heating or cooling delivered by a heating or cooling system, as measured in BTUs or tons.
• Capacitor: An electrical component that can store energy.
• Capillary Tube System: Refrigerant control system consisting of a small bore tube.
• Carbon Monoxide (CO): CO is a colourless, odourless and poisonous gas.
• Carbon Monoxide Alarm: A warning device to signal the presence of CO.
• Carbon Usage Effectiveness (CUE): A measure of the efficiency of a data center’s carbon footprint.
• Celsius: A system for measuring temperature in which water freezes at 0 degrees and boils at 100 degrees.
• Centrifugal Fan: A fan that uses air or other gases to create a flow.
• Central Air: A system that cools air at a central locati0n and delivers it to and from rooms by one or more fans and ductwork.
• CFM (Cubic Feet Per Min): Amount of air volume flowing through the unit.
• Check Valve: A valve that permits flow in only one direction.
• Chiller: A device incorporating a refrigeration cycle to lower the temperature of a liquid.
• CIBSE (Chartered Institution of Building Services Engineers): A membership body for engaging, inspiring and informing the building services community.
• CITB (Construction Industry Training Board): A training body for construction trade.
• Clean Room: A room with reduced pollutants.
• Climate control: The close and precise control of an environment.
• Coil: A device that transfers heat to air, usually with the aid of refrigerant or water chemicals.
• Combined Annual Electric Efficiency Rating (CAE): A unit’s total energy efficiency.
• Commercial AC: Air conditioning in large commercial buildings.
• Commissioning: A service by which the proper operation of equipment is verified.
• Composite Fan Blades: Fan blades which are composed of composites.
• Compressor: The element of the system that compresses the refrigerant.
• Condenser: The outdoor part of the system that throws off heat.
• Condenser Coil: The outdoor part of the unit that changes the refrigerant from a gas into a liquid.
• CAV (Constant Air Volume): A system that maintains a constant volume of air.
• Controller: A machine that regulates an operation of a system.
• CWR (Chilled Water Return): Piping which carries chilled water from the load to the chiller.
• CWS (Chilled Water Supply): Piping to convey chilled water from the chiller to the load.
• CSA (Canadian Standards Association) An organization responsible for testing and listing electrical products and other safety-related equipment.
• Cycling: The operation of the HVAC system in which it is repeatedly turned on and off.

D

• Damper: A movable plate in ductwork that controls the flow of air.
• Data Center: a building mainly used for storage of computers and related components.
• dB (Decibels): A unit that measures sound intensity.
• DC (Direct Current): An electric current that flows in one direction.
• Decant/receiver:  A vessel in the refrigeration system in which liquid refrigerant is stored.
• Degree-Day: A measure of heating or cooling needed, defined as the difference between the average outdoor temperature and a base temperature.
• Dehumidifier: A mechanical appliance that removes humidity from the air.
• Deep Lake Water Cooling: to chill with deep lake water.
• ΔT (delta T): The variation of temperature.
• Diffuser: A grille through which air is directed in some predetermined manner.
• DOE (Department of Energy): A government department of the United States concentrating on energy.
• Downflow Furnace: A fur-nace having an inlet on the top andthe outlet on the bottom.
• Drain Pan: A pan that receives the condensate.
• Drier: A filter in the refrigeration system that filters out contaminants.
• Dry Bulb Temperature: Temperature that is measured without taking humidity into consideration.
• Dry Charge: An air conditioner whose compressor comes charged with refrigerant at the time of installation, as opposed to one that is shipped pre-charged.
• Dual-Fuel: A heating system that includes a heat pump and a gas furnace.
• Duct: A channel-like housing for air flow.
• Ductwork: Tubes or channels through which air travels in a building.
• Ductless mini split: A system with an outdoor compressor and indoor air handler(s), without ductwork.

E

• ECM Motor: Direct Drive Motor A highly efficient, electronically commutated motor that enhances the unit’s capacity to dry the sensor quickly.
• Economizer: A machine of an HVAC system which takes in air from outside to minimize energy usage.
• EER (Energy Efficiency Ratio): This is a ratio of cooling output to the power consumption.
• EER2: ( Energy Efficiency Ratio 2) A term used to rate the cooling capacity of air conditioners and heat pumps.
• EAC (Electronic Air Cleaner): A type of air cleaner that uses electrically charged filters to reduce the amount of contaminants in the air.
• Electronic Air Filter: A filter that can be installed on your duct work and performed whole home filtration.
• Enthalpy: Total air heat content.
• Energy Star: A program that designates energy-efficient products.
• EPA (Environmental Protection Agency) : Federal agency for environmental regulation.
• Evaporator: A device in which heat is added or extracted from the system.
• Evaporator Coil: Found in the air handler, it removes warmth from the air.
• Expansion valve: A component of refrigerant flow control.

F

• Fan Coil Unit (FCU): Equipment that uses a coil and a fan to warm or cool a room directly without having ductwork.
• Filter: This is a mechanism which holds dust and dirt.
• Flue: A vent to carry off the products of combustion.
• Flex: A duct that is flexible, designed for tight spaces.
• Float Switch: The equipent which disengages the system to prevent overflowing.
• Flow: The volume of fluid that crosses a given area in a unit time.
• Fresh Air Fan (FAF): Fan that suck in outside air.
• Fresh Air Fraction (faf): Measures the performance of an economizer.
• Fresh Air Intake (FAI): An opening that allows outside air into a building.
• Freon™: A brand name for R22 refrigerant, which is now being phased out.
• Furnace: An apparatus that warms air, usually with gas, oil or electricity.

G

• Garage Heaters: Heaters that are designed for car garages.
• Gas Furnace: A heating system that uses natural gas or propane.
• Gas Package: A combined AC and heater system offering gas heating and electric air conditioning.
• Gas Valve: A gas regulating device.
• Gas Furnace Heat Exchanger: Moves heat from furnace into air.
• Geothermal Heat Pump: A heat pump that relies on the constant temperature of the earth to cool and heat the house.
• Grid-Tie Inverter Solar System: This is a solar system you can use which uses your utility grid as backup.
• Grille: A grill or screen covering an opening in a duct and serving to direct air flow.
• GWP (Global Warming Potential) : A way of indicating how much of a contribution a substance makes to global warming.

H

• Head Pressure: Pressure in the condensing part of the system.
• Heat Exchanger: A machine for the transfer of heat between a cold and hot fluid.
• Heat Gain: The quantity of heat that is added to a space.
• Heat loss: The extent of heat leaked from a space.
• Heat Load Analysis: A calculation to calculate the heating or cooling requirements for a building or room.
• Heat Pump: An hvac that heats or cools using mechanical means to move heat.
• Heat Source: The body from which heat is extracted.
• Heat Transfer: The transfer of thermal energy.
• Heating Coil: A coil used to heat.
• HEPA filter: A filter which reduces airborne particles.
• High Performance Computing (HPC): Using combined computing power to solve large problems.
• Horizontal: A furnace or air handler lying on its side.
• Hot Aisle: A method of hot-aisle/cold-aisle server rack layout in which servers expel hot exhaust.
• HSPF: The measurement of a heat pump’s heating efficiency over an entire warm season.
• HSPF2 (Heating Seasonal Performance Factor 2): A measure of the efficiency of heat pumps.
• Humidifier: An apparatus that releases moisture into the air.
• Humidistat: An instrument that controls the relative humidity in a space.
• Humidity: Moisture in the air as water vapor.
• Hybrid Heat: A combination system of heat pump and gas.
• Hydrocarbon Refrigerant (HC): A refrigerant consisting of carbon and hydrogen.
• HFC (Hydroflurocarbon): A non ozone depleting, high global warming refrigerant.
• HFO (Hydrofluoroolefin): A refrigerant with zero ODP and low global warming potential.

I

• IAQ (Indoor Air Quality): The condition of the indoor air around a region.
• Ignition: The process of lifting a material to the point of combustion.
• Indoor Coil: Also known as Evaporator Coil.
• Industrial fridge: Refrigeration appliances that are used for low temperature food processing.
• Interconnect Agreement: Power systems that are physically connected or tied to each other.
• ISPs: Internet Service Provider(s).
• Inverter Compressor: Compressor that changes from the usual fixed speed to a different speed.
• ISO 9000 [ISO/IEC 9000]: International standards on quality management.

K

• Kilowatt (kW): A measure of energy flow.
• Kyoto Protocol: An international agreement to regulate global warming.

L

• Latent Cooling Capacity: The cooling capacity providing a change in temperature without changing humidity.
• Latent Heat: Energy given off or absorbed during a phase change.
• LEED (Leadership in Energy and Environmental Design): A green building rating system.
• Leak Detector: Implement for identification of refrigerant leakage.
• Line Set: Pipes that carry refrigerant in a split system.
• Liquid Line: A line that transports the liquid refrigerant.
• Load Analysis: A survey of energy requirements for sizing a system.
• Louver: Blades which adjust airflow.
• Low Boy: A furnace or air handler that is made to fit into tight spaces.
• Low Stage: Stage in a multistage compressor system at a lower refrigerant pressure.

M

• Make Up Air Unit (MUA): Makeup Air Unit An air handling unit which conditions 100% outside air.
• Manual J: A method to determine heat load.
• Manufacturer Approved System: A system that the manufacturer is approved and deliver optimum performance.
• Mastic: A putty-like coating for sealing ducts.
• Matched System: An indoor and outdoor cooling or heating unit that has been specifically paired for efficiency ratings and operation.
• Media: The substance that a filter is made of.
• MERV Rating: The air filter efficiency rating.
• Micron: A measuring unit that is equivalent to one millionth of a meter.
• Microchannel Coil: A coil design that incorporates use of miniature channels for heat transfer.
• Micron Gauge:  A device that measures vacuum in microns.
• Mini Split o Ductless System: A small outdoor unit and wall mounted indoor unit that makes up for a cooling system.
• Minimum Outside Air: The minimum amount of outdoor air permitted within a system.
• Mineral Oil: A type of lubricating oil used in some older HVAC systems.
• Modulating Heating:  Heat that adjusts with the temperature.
• Multipoise: A furnace that has more than one positioning for the ducting.

N

• N+1: It’s just a way of having redundancy deployed in the data center.
• NATE (North American Technician Excellence): A credentialing program for HVAC technicians.
• NEC (National Electric Code): The code that provides rules for safe electrical installations.
• NEMA (National Electrical Manufacturing Association): Electrical manufacturers association.
• Net Metering: A procedure that applies credits for solar system owners that generated more energy and has introduced the power back into the grid.
• N2 (Nitrogen): A gas for purging and pressure testing.

O

• Oil furnace: A gas furnace that uses heating oil.
• Orifice: A passage used to regulate the flow of fluid.
• Outdoor Air Damper: A damper that regulates the flow of outdoor air.
• Outside Air Temperature (OAT): Refer to outside air temperature.
• Overload Protectors: An instrument that shuts down activity in circumstances that are unsafe.
• Outdoor Coil: See Condenser.

P

• Packaged Unit: A heating and/or cooling unit contained in one outdoor unit.
• Packaged Terminal Air Conditioner (PTAC): Another term for a small AC and heating unit that fits into a wall.
• PAG (Polyalkylene glycol): Synthetic oil used in AC systems.
• Particulates: Fine matter whether solid or liquid.
• Return Plenum: An area designed to conduct airflow.
• Pressure & Strength Testing: Testing for system integrity.
• Programmable Thermostat: A thermostat that can be programmed with a schedule.
• Psychrometric Chart: A plot of air conditions.
• Psychrometric: The science of air-water vapour mixtures.
• PUE (Power Usage Effectiveness): A standard for calculating the energy efficiency of a data center.
• PVC (Polyvinyl chloride): Used in sauces, pipes pantings and other construction supplies.

R

R22 (Freon): Refrigerant that is being phased out.

R32 Refrigerant: An HVAC refrigerant.

R-410A Refrigerant: Non-ozone depleting refrigerant.

R-454B Refrigerant: Low GWP Refrigerant.

R-Number: A number given to a refrigerant by a certifying agency.

Radiant Ceiling Panels: Metal plates employed for heating/cooling.

Radiant Floor: A method of heating in which hot fluids are distributed through the floor.

Radiation: Transfer of heat from one surface directly to another.

Recovery: Recovering′ means the processing refrigerant to the specifications prescribed in the rules of the EPA.

Reciprocating Compressors: Compressor featuring a piston.

Refrigerant: A material that cools.

Refrigerant Charge: The quantity of refrigerant in a system.

Refrigeration Lines: Tubing to deliver and remove refrigerant to and from system.

Refrigeration Cycle (Vapour Compression Cycle): The cycle of absorbing and rejecting heat by the refrigerant.

Register: A grille/damper at the end of a duct.

Relative Humidity (%rh): Water vapor pressure divided by saturation vapor pressure.

Remote Electronic Expansion Valve (REEV): An expansion valve with a remote panel.

Retrofit: To replace or modify the refrigerant system.

Riello Burner: The burner portion in an oil furnace.

Return Air: Air that is drawn back to the HVAC system.

RCI (HI) & RCI (LO): A measure of data center cooling.

Rooftop Unit (RTU): A unit that is self-contained and installed on a roof.

R-Value: Resistance to the flow of heat.

S

• Scroll Compressor: A compressor that runs in a smooth circular motion.
• SEER (Seasonal Energy Efficiency Ratio): The rating of air conditioning energy efficiency.
• SEER2: An energy comparison rating for air conditioning systems.
• Self-Contained: Just another way of saying package unit.
• Sensible Cooling Capacity:  Energy to cool the air without any change in humidity.
• Sensible Heat: Heat that produces a change in the temperature of a substance or heating medium.
• SHR (Sensible Heat Ratio): Ratio of Sensible Heat to Total Heat.
• Sensor: An object that responds to a change in environment.
• Server: A system that services network requests.
• SilentComfort™ Outdoor Fan Motor: A motor that doesn’t create a lot of noise.
• Single Unit: When all its parts are located in a single unit.
• Single-Speed: A motor that operates at full speed until the desired temperature is reached.
• Smoke Damper: A damper that is installed to aid the ventilation in a fire.
• Split: A system with separated indoor and outdoor units.
• Subcooling: Refrigerant being cooled because it is at a temperature lower than the saturation temp.
• Suction Pressure: Pressure at the low side of the compressor.
• Superheat: Heating of vapor above its boiling point.
• Supplementary Heat: Back-up or emergency heat.
• System: A blanket name for HVAC parts.

T

• Terminal Unit (TU): A device to regulate room temperature that serves only one room.
• Thermidistat: Monitors both temperature and humidity with a device.
• Thermostat: The device which manages the output of an HVAC.
• Thermostatic Expansion Valve (TEV or TXV): A valve which controls the flow of refrigerant.
• Thyristor: A semiconductor device in the form of a switch.
• Ton: A standard of energy for cooling, equivalent to 12,000 BTUs per hour.
• Turning Vane: Device used in duct work intended to enhance air flow.
• Two-Speed: A two-speed motor for better efficiency.
• TWO STAGE OPERATION: Offer two levels of heat or cool.

U

• UL (Underwriters Laboratories): A company that tests products for safety.
• UV Lamps: Light bulbs that disinfect bacteria, mold, or mildew in an HVAC system.
• Underfloor Air Distribution (UFAD): This uses the underfloor plenum to distribute air.
• Upflow Furnace: A type of furnace that draws in air from the bottom and expels it through the top.
• Unitary Controller: A controller for a single zone in a building.

V

• Vacuum: A region of space whose pressure is much less than atmospheric pressure.
• Variable Speed Motor: Motor that runs at various speeds.
• Variable Air Volume (VAV): A system that modulates the airflow in response to temperature needs.
• Ventilation: The movement of air into and out of a space.
• Ventilator: A unit that heats fresh air and expels stale or foul-smelling air.
• Volt: A unit for electric potential.
• Voltage: The pressure that motivates electric current.

W

• Watt: A unit of measure to indicate the rate of energy conversion.
• Wet Bulb Thermometer: A thermometer that registers humidity.

Z

• Zeotrope: A blend of refrigerants which does not deviate in composition from the refrigerant and the refrigerant breaks up into its components.
• Zoning: A system that separates an area into different temperature zones.

Why It’s Important to Know HVAC Terms

Look, I get it. All this can be overwhelming. But here’s why it matters:

• Informed decisions: When it comes time to replace your HVAC system again, you’ll be able to find exactly what you’re looking for — instead of flying blind. You’ll know what the efficiency ratings, such as SEER and AFUE, mean, whether you need a heat pump or a furnace, and whether you want a split system or a packaged unit.
• Smart Investments: Understanding the lingo helps you select systems that fit both your needs and your budget.
• Communication: Ever tried to have a conversation with a technician whose first language wasn’t the same as yours? Not anymore. With this insight, you also can communicate your issues more clearly and understand the solutions that are proposed.
• Preventative Maintenance: When you know how parts (ex: compressor, condenser and evaporator coil) are supposed to work, you will be able to monitor your system.

FAQs About HVAC Terminology

Q: What does SEER mean?

A: SEER is an acronym for Seasonal Energy Efficiency Ratio. It is a measure of the cooling performance of air conditioners and heat pumps. The higher the SEER, the more energy efficient the unit is.

Q: What is AFUE?

A: AFUE is the acronym for Annual Fuel Utilization Efficiency. It’s an indicator of how efficiently a furnace turns fuel into heat. A higher AFUE indicates that the furnace is more efficient.

Q: What is a BTU?

A: A BTU (British Thermal Unit) is a unit of measure of heat energy. It is the amount of energy needed to raise a pound of water one degree Fahrenheit.

Q. What’s the difference between a humidifier and a dehumidifier?

A: A humidifier puts moisture in the air; a dehumidifier takes moisture out. Both have an impact on the comfort of indoors.

Wrapping Up

Well there you have it—a guide to HVAC terminology to aid in your journey through the world of heating and cooling. You see, the more you know about HVAC language, the closer you are to controlling your indoor environment. It’s really just about being smart, and staying informed, and knowing what the right choices are for your space. Now, take your new knowledge out there and sound like you actually know HVAC.