Plain-English reference
HVAC glossary
The terms you'll see on a quote or hear from a tech, defined the way we'd explain them to a neighbor. No jargon left unexplained — and where a term has a full guide, we link straight to it.
A–Z reference
Every HVAC term, defined
18 of the words that come up most when you plan, price, or troubleshoot a system in the DMV — in plain English, with deeper guides where they help.
- SEER2
- The current (2023+) seasonal cooling-efficiency rating for ACs and heat pumps. Higher is more efficient; new systems must meet a federal minimum that varies by region. Learn more about SEER2
- AFUE
- Annual Fuel Utilization Efficiency — how much of a furnace's fuel becomes heat. A 96% AFUE furnace turns about 96 cents of every fuel dollar into warmth.
- HSPF2
- Heating Seasonal Performance Factor 2 — the heating-efficiency rating for a heat pump. The higher the number, the less electricity it uses to keep you warm.
- Heat pump
- One all-electric system that both heats and cools by moving heat instead of burning fuel. Modern cold-climate models heat efficiently through DMV winters. Learn more about Heat pump
- Ductless mini-split
- A heat pump with an outdoor unit feeding one or more wall- or ceiling-mounted indoor heads — no ductwork. Great for additions, finished basements, and problem rooms. Learn more about Ductless mini-split
- Manual J
- The industry-standard, room-by-room load calculation that determines the correct system size for your home — the right way to size equipment, not a square-footage guess. Learn more about Manual J
- Tonnage
- A measure of cooling capacity: one ton equals 12,000 BTU per hour. Most homes need 2–5 tons, set by a Manual J calculation rather than floor area alone. Learn more about Tonnage
- BTU
- British Thermal Unit — the basic unit of heating and cooling energy, used to rate furnace output and air-conditioning capacity.
- R-410A
- A refrigerant used in most systems sold over roughly the last 15 years. It's being phased down, so the newest equipment ships with lower-impact refrigerants.
- R-454B
- A newer, lower-global-warming refrigerant replacing R-410A in 2025-and-later equipment. You may also see it branded as Puron Advance.
- R-22 (Freon)
- An older refrigerant phased out in 2020. It's no longer produced, so recharging an R-22 system gets pricier every year — a key repair-vs-replace factor.
- MERV
- Minimum Efficiency Reporting Value — how well an air filter traps particles (1–16 for homes). Higher catches more, but too high can choke airflow, so match it to your system. Learn more about MERV
- Variable-speed (inverter)
- A compressor or blower that ramps smoothly up and down instead of just switching on and off — steadier temperatures, better humidity control, and lower bills. Learn more about Variable-speed (inverter)
- Zoning
- Dampers and multiple thermostats that heat or cool areas of the home independently — the fix for an upstairs that's always hot or a bonus room that's always cold. Learn more about Zoning
- Air handler
- The indoor unit — blower plus coil — that circulates conditioned air. It pairs with a heat pump or AC in homes that don't have a furnace.
- Condenser
- The outdoor unit that releases the heat pulled from your home — the big box with the fan that sits beside the house.
- Heating / cooling load
- How much heating or cooling your home actually needs, driven by insulation, windows, and air leakage, and measured by a Manual J calculation. Learn more about Heating / cooling load
- Static pressure
- The resistance air meets moving through your ducts. Too high strains the blower and wastes energy — often a sign of undersized or restricted ductwork.
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