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 expands without heat exchange with surroundings.

B–C

BTU (British Thermal Unit) — Unit of heat energy; the amount needed to raise 1 lb of water by 1°F.

Capacitor — Electrical component that stores energy to start or run HVAC motors.

CFM (Cubic Feet per Minute) — Measurement of airflow volume through an HVAC system.

Chiller — A machine that removes heat from a liquid via vapor-compression or absorption refrigeration cycle.

D–E

Damper — A valve or plate that regulates airflow inside a duct, chimney, or HVAC system.

EER (Energy Efficiency Ratio) — Ratio of cooling output to power input at a specific operating condition.

Enthalpy — Total heat content of air, including both sensible and latent heat.

Evaporator Coil — The indoor coil that absorbs heat from indoor air during the cooling cycle.

F–H

Filter Drier — A device that removes moisture and contaminants from refrigerant.

Heat Pump — A system that transfers heat between indoors and outdoors for both heating and cooling.

HSPF (Heating Seasonal Performance Factor) — Efficiency rating for heat pumps in heating mode.

Humidistat — A device that measures and controls humidity levels.

I–M

IAQ (Indoor Air Quality) — The quality of air within buildings as it relates to health and comfort.

Lineset — Copper tubing connecting the indoor and outdoor units of a split system.

Manifold Gauge Set — A tool used to measure refrigerant pressures in HVAC systems.

Mini-Split — A ductless HVAC system with separate indoor and outdoor units.

N–R

R-410A — A common HFC refrigerant used in residential HVAC systems (being phased out).

R-32 — A lower-GWP refrigerant increasingly used in modern HVAC equipment.

R-454B — An A2L refrigerant replacing R-410A in new equipment under EPA regulations.

Refrigerant Charge — The amount of refrigerant in an HVAC system.

S–T

SEER (Seasonal Energy Efficiency Ratio) — Cooling efficiency rating over a typical cooling season.

Subcooling — The process of cooling refrigerant below its condensing temperature.

Superheat — The temperature of refrigerant vapor above its boiling point at a given pressure.

TXV (Thermostatic Expansion Valve) — A metering device that controls refrigerant flow into the evaporator.

U–Z

VAV (Variable Air Volume) — An HVAC system that varies airflow at a constant temperature.

VRF (Variable Refrigerant Flow) — A multi-zone system using refrigerant as the cooling/heating medium.

Wet Bulb Temperature — Temperature measured by a thermometer with a wet wick; indicates humidity.

Zoning — Dividing a building into separate areas with independent temperature control.