Reference
HVAC terms, in plain English.
Definitions for the words that show up on estimates and spec sheets — each linked to the guides and services that put them in context.
AFUE
Annual Fuel Utilization Efficiency — the percentage of fuel a furnace turns into usable heat over a …
Define →Air Handler
The indoor unit that circulates conditioned air through your ductwork. Paired with a heat pump or AC…
Define →BTU
British Thermal Unit — the standard measure of heating or cooling energy. The higher the BTU rating,…
Define →Capacitor
A small component that stores and releases the jolt of electricity needed to start and run motors. A…
Define →Compressor
The heart of an AC or heat pump — it pressurizes refrigerant and moves it through the system. Replac…
Define →Condensate Drain Line
The pipe that carries away the water your AC pulls from the air. A clogged drain line is a frequent …
Define →Condenser
The outdoor unit that releases heat pulled from your home. Keeping it clean and clear of debris is k…
Define →Damper
A movable plate inside ductwork that controls airflow to different areas of the home — the building …
Define →Dual-Fuel System
A heat pump paired with a gas furnace. The heat pump handles mild weather efficiently and the furnac…
Define →Ductless Mini-Split
A heating and cooling system that needs no ductwork. An outdoor unit feeds one or more wall- or ceil…
Define →Ductwork
The network of channels that distributes heated and cooled air through your home. Leaky or poorly de…
Define →EER
Energy Efficiency Ratio — a measure of cooling efficiency at a specific high temperature. Useful for…
Define →Evaporator Coil
The indoor coil where refrigerant absorbs heat from your home's air. When it ices over, you lose coo…
Define →Furnace
The appliance that heats air by burning gas (or using electricity) and pushes it through your ducts.…
Define →Heat Exchanger
The furnace component that transfers combustion heat to your home's air while keeping exhaust gases …
Define →Heat Pump
A system that moves heat rather than burning fuel — cooling in summer and heating in winter. Cold-cl…
Define →HEPA Filter
High-Efficiency Particulate Air filter — captures 99.97% of particles down to 0.3 microns, including…
Define →HSPF
Heating Seasonal Performance Factor — the efficiency rating for a heat pump's heating mode. Higher H…
Define →Humidifier (Whole-Home)
A unit added to your HVAC system that adds moisture to dry winter air, improving comfort and protect…
Define →HVAC
Heating, Ventilation, and Air Conditioning — the umbrella term for the systems that control your hom…
Define →Indoor Air Quality (IAQ)
The cleanliness and healthfulness of the air inside your home, shaped by filtration, ventilation, hu…
Define →Load Calculation (Manual J)
The industry-standard math used to size equipment to your specific home. Skipping it leads to oversi…
Define →MERV Rating
Minimum Efficiency Reporting Value — rates how well an air filter captures particles, from 1 to 16. …
Define →Plenum
The central air distribution box attached to your furnace or air handler where supply and return duc…
Define →Refrigerant
The chemical that cycles through your AC or heat pump, absorbing and releasing heat. Modern systems …
Define →Return Air
The air pulled back into your system to be reconditioned. Adequate return airflow is essential for e…
Define →SEER2
Seasonal Energy Efficiency Ratio 2 — the current standard rating for cooling efficiency over a seaso…
Define →Short Cycling
When a system turns on and off too frequently, never completing a full cycle. It wears out component…
Define →Smart Thermostat
A connected thermostat that learns your schedule and lets you control your system from your phone, t…
Define →Static Pressure
The resistance to airflow inside your duct system — like blood pressure for your HVAC. Too high stra…
Define →Thermostat
The control that tells your system when to heat or cool. Programmable and smart models can cut energ…
Define →Ton (of Cooling)
A unit of cooling capacity equal to 12,000 BTU/hour. A typical home needs 2–5 tons, sized by a load …
Define →Two-Stage System
Equipment that runs on a lower setting most of the time and ramps to full power only when needed — q…
Define →Variable-Speed Blower
A blower motor that adjusts its speed continuously for precise comfort, better humidity control, and…
Define →Zoning
Dividing a home into independently controlled areas using dampers and thermostats, so you heat or co…
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