HVAC Glossary

AFUE Rating

AFUE (Annual Fuel Utilization Efficiency) measures how much of a furnace or boiler's fuel becomes usable heat …

Air Balancing

Air balancing is the process of measuring and adjusting airflow at each supply register so every room receives…

Air Handler

An air handler is the indoor unit that moves air through a home's ductwork. It contains a blower motor, an eva…

Boiler

A boiler is a heating appliance that heats water (or makes steam) and circulates it through radiators, baseboa…

BTU

A BTU (British Thermal Unit) is the amount of heat needed to raise one pound of water by one degree Fahrenheit…

Carbon Monoxide Safety

Carbon monoxide safety covers the practices that prevent CO poisoning from fuel-burning appliances such as fur…

Compressor

The compressor is the pump at the heart of an air conditioner or heat pump. It pressurizes refrigerant vapor, …

Condensate Line

A condensate line is the small drain pipe that carries water away from an air conditioner or high-efficiency f…

Condenser Coil

The condenser coil is the network of refrigerant tubing and fins in the outdoor unit of an air conditioner or …

Dryer Vent

A dryer vent is the duct that carries hot, moist, lint-laden air from a clothes dryer to the outdoors. Lint gr…

Ductless Mini-Split

A ductless mini-split is a heat pump system that conditions rooms without ductwork. A compact outdoor unit con…

Evaporator Coil

The evaporator coil is the indoor coil of an air conditioner or heat pump, usually mounted above the furnace o…

Heat Exchanger

A heat exchanger is the metal component inside a furnace that transfers heat from burning fuel to the air circ…

Heat Pump

A heat pump is a reversible refrigeration system that both heats and cools a home. In summer it works like an …

Heat Strip / Auxiliary Heat

A heat strip, also called auxiliary or electric resistance heat, is a bank of electric heating elements instal…

HSPF2 Rating

HSPF2, or Heating Seasonal Performance Factor 2, measures a heat pump's heating efficiency: total seasonal hea…

Indoor Air Quality / IAQ

Indoor air quality, or IAQ, describes how clean and healthy the air inside a building is, considering particul…

Load Calculation / Manual J

A load calculation, performed using the ACCA Manual J method, determines how much heating and cooling a home a…

Makeup Air Unit

A makeup air unit is a ventilation system that draws in outdoor air, filters and conditions it, and delivers i…

MERV Rating

MERV (Minimum Efficiency Reporting Value) rates how effectively an air filter captures particles, on a scale f…

Oil Furnace

An oil furnace burns heating oil delivered to an on-site tank, using a pressurized burner to atomize and ignit…

Plenum

A plenum is the sealed sheet-metal box that connects a furnace or air handler to the duct system. The supply p…

Refrigerant

Refrigerant is the working fluid in air conditioners and heat pumps that absorbs heat as it evaporates indoors…

Refrigerant Charge

Refrigerant charge is the precise amount of refrigerant circulating in an air conditioner or heat pump, specif…

Return Duct

Return ducts pull air from living spaces back to the furnace or air handler to be filtered and reconditioned. …

Rooftop Unit / RTU

A rooftop unit, or RTU, is a self-contained packaged HVAC system installed on a flat roof, most often on comme…

SEER2 Rating

SEER2 (Seasonal Energy Efficiency Ratio 2) measures how efficiently an air conditioner or heat pump cools over…

Short Cycling

Short cycling is when a furnace, air conditioner, or heat pump turns on and off in rapid, brief bursts instead…

Static Pressure

Static pressure is the resistance to airflow inside an HVAC system's ductwork, measured in inches of water col…

Supply Duct

Supply ducts are the channels that carry heated or cooled air from your furnace, air handler, or heat pump out…

Thermostat (Smart Thermostat)

A thermostat is the control that senses indoor temperature and tells your heating and cooling equipment when t…

Two-Stage Furnace

A two-stage furnace has a gas valve that operates at two output levels: a reduced first stage for mild weather…

UV Air Purifier

A UV air purifier installs inside ductwork or near the evaporator coil and uses ultraviolet (UV-C) light to ne…

Variable-Speed Blower

A variable-speed blower is a furnace or air handler fan driven by an electronically commutated motor (ECM) tha…

Whole-House Humidifier

A whole-house humidifier mounts on the furnace or air handler and adds moisture to air as it circulates throug…

Zoning System

A zoning system divides a home into independently controlled heating and cooling areas using motorized dampers…