HVAC Glossary of Terms
Definitions for common HVAC, refrigeration, system, component, refrigerant, airflow, and service-tool terminology used by contractors, technicians, facility maintenance teams, and commercial buyers.
Important Notice
This glossary is provided for general educational reference only. It should not be used as a substitute for manufacturer documentation, code requirements, engineering guidance, or professional installation and service advice.
Glossary Definitions
A
AHU (Air Handling Unit) — A device used to regulate and circulate air as part of an HVAC system.
AFUE (Annual Fuel Utilization Efficiency) — A measure of a furnace's efficiency in converting fuel to heat over a typical year.
Adiabatic Cooling — Cooling that occurs when air changes state or pressure without direct heat exchange with surrounding air.
B–C
BTU (British Thermal Unit) — A unit of heat energy commonly used to describe HVAC heating or cooling capacity.
Capacitor — An electrical component that stores energy and helps start or run HVAC motors.
CFM (Cubic Feet per Minute) — A measurement of airflow volume through an HVAC system.
Chiller — Equipment that removes heat from a liquid using a refrigeration or absorption process.
D–E
Damper — A device or plate used to regulate airflow within ducts or HVAC systems.
EER (Energy Efficiency Ratio) — A cooling efficiency ratio measured under specific operating conditions.
Enthalpy — The total heat content of air, including sensible and latent heat.
Evaporator Coil — The coil that absorbs heat from indoor air during the cooling cycle.
F–H
Filter Drier — A device used to help remove moisture and contaminants from refrigerant circuits.
Heat Pump — A system that transfers heat between indoor and outdoor spaces for heating or cooling.
HSPF (Heating Seasonal Performance Factor) — A heating efficiency rating used for heat pumps.
Humidistat — A device used to measure or control humidity levels.
I–M
IAQ (Indoor Air Quality) — The quality of air inside buildings as it relates to health, comfort, ventilation, and contaminants.
Lineset — Copper tubing that connects indoor and outdoor units in a split HVAC system.
Manifold Gauge Set — A tool used to measure refrigerant pressures during HVAC service work.
Mini-Split — A ductless HVAC system using separate indoor and outdoor units.
N–R
R-410A — A common HFC refrigerant used in many existing HVAC systems.
R-32 — A lower-GWP refrigerant used in some newer HVAC equipment.
R-454B — An A2L refrigerant used in newer HVAC equipment as part of the industry transition away from higher-GWP refrigerants.
Refrigerant Charge — The amount of refrigerant contained in or added to an HVAC system.
S–T
SEER (Seasonal Energy Efficiency Ratio) — A cooling efficiency rating over a representative cooling season.
Subcooling — Cooling liquid refrigerant below its condensing temperature.
Superheat — Heating refrigerant vapor above its saturation temperature at a given pressure.
TXV (Thermostatic Expansion Valve) — A metering device that regulates refrigerant flow into an evaporator coil.
U–Z
VAV (Variable Air Volume) — An HVAC system that varies airflow to control conditions in different zones.
VRF (Variable Refrigerant Flow) — A multi-zone HVAC system using refrigerant to serve multiple indoor units.
Wet Bulb Temperature — Temperature measured using a wetted sensor, useful for humidity and psychrometric calculations.
Zoning — Dividing a building into separate control areas with independent temperature or airflow control.
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