HVAC terms, in plain English

Efficiency ratings

SEER2

Cooling efficiency over a season. Higher means less electricity for the same cooling. It replaced SEER in 2023 with a tougher test, so a SEER2 number reads slightly lower than the old SEER for the same unit. 14 is the current baseline; 16 to 18 is mid-tier; 20+ is premium.

EER2

Cooling efficiency at one fixed, hot condition (95°F outside) instead of a seasonal average. Useful if you live somewhere with long stretches of extreme heat.

HSPF2

The heating version of SEER2, for heat pumps. Higher means cheaper winters. 7.5 is baseline; 8.5+ is good.

AFUE

The share of gas a furnace turns into heat. An 80% furnace sends a fifth of your gas bill up the flue; a 95%+ condensing furnace keeps nearly all of it and vents in cheap PVC pipe. In cold climates the upgrade usually pays for itself.

Sizing

Ton / BTU

Capacity, not weight. One ton of cooling is 12,000 BTU per hour. Most homes need 2 to 5 tons. Bigger is not better: an oversized unit cools fast but shuts off before it removes humidity.

Manual J

The real load calculation: room-by-room math on your square footage, insulation, windows, and climate. Any sizing based only on square footage is a rule of thumb, and rules of thumb usually run a half ton or more too big. Ask for the Manual J before you buy up a size.

AHRI match

The certified pairing of an outdoor unit with a specific indoor coil or air handler. Mismatched pairs lose rated efficiency and can void the warranty. The AHRI certificate number should appear on your quote.

Equipment types

Heat pump

An air conditioner that also runs in reverse, so one system heats and cools. Modern cold-climate models work well below freezing.

Condenser

The outdoor box of a split system. Its price is only half the system; it needs a matched indoor coil or air handler.

Air handler

The indoor fan unit that moves air through your ducts when there is no furnace, typically paired with a heat pump.

Evaporator coil

The indoor coil that actually cools the air, mounted on your furnace or air handler. Replaced together with the condenser in most changeouts.

Mini-split / ductless

An outdoor unit feeding one or more wall-mounted indoor heads, no ductwork needed. Single-zone covers one room; multi-zone systems run several heads off one outdoor unit and cost accordingly.

Package unit

The whole system in one outdoor cabinet, common on roofs and slab-mounted installs in the South and Southwest.

PTAC

The through-the-wall units you see in hotels. Cheap per room, no ducts, one room each.

On your quote

Single-stage / two-stage / variable

How the compressor runs: on-off, two speeds, or a continuous range. Each step up costs more and improves comfort and humidity control. Variable matters most in humid climates and large homes.

R-410A vs R-454B and R-32

The refrigerant generation change. New equipment ships with lower-global-warming refrigerants (R-454B, R-32); R-410A equipment is the outgoing stock. Both work; parts and refrigerant for the old generation will get pricier over time.

Line set

The pair of copper pipes connecting the indoor and outdoor units. Long or buried runs add real labor cost; reusing an old line set on a new refrigerant needs flushing or replacement.

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