SEER2
Seasonal Energy Efficiency Ratio 2 — the current U.S. cooling-efficiency rating method used for systems manufactured after 2023. Higher SEER2 generally means lower cooling cost for the same capacity.
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HVAC glossary
Entity definitions used across our residential and commercial guides — so quotes and inspections make sense the first time.
HSPF2
Heating Seasonal Performance Factor 2 — the heating-side efficiency rating for heat pumps under the updated test procedure.
EER
Energy Efficiency Ratio — cooling efficiency at a single outdoor design condition. Useful when comparing peak-load performance in hot inland valleys.
BTU
British Thermal Unit — a measure of heating or cooling capacity. Residential systems are often discussed in tons (1 ton ≈ 12,000 BTU/h).
AFUE
Annual Fuel Utilization Efficiency — how efficiently a gas furnace converts fuel into heat over a typical season.
MERV rating
Minimum Efficiency Reporting Value — filter efficiency scale. Higher MERV captures finer particles; confirm your blower can handle the pressure drop.
R-410A
The common residential refrigerant being phased down. New equipment is shifting to lower-GWP alternatives in California.
R-454B
A lower-GWP A2L refrigerant used in many next-generation residential systems replacing R-410A.
R-32
A lower-GWP A2L refrigerant used by some manufacturers as an R-410A successor.
ECM blower motor
Electronically commutated motor — variable-speed blower that improves comfort, humidity control, and efficiency versus single-speed PSC motors.
Evaporator coil
Indoor coil where refrigerant absorbs heat from indoor air during cooling.
Condenser
Outdoor unit heat exchanger that rejects heat outdoors during cooling (and absorbs heat outdoors during heat-pump heating).
Compressor
The pump that circulates refrigerant and creates the pressure difference that drives heat transfer.
Heat pump
A system that moves heat rather than generating it with combustion — cooling in summer and heating in winter from one outdoor unit.
Ductless mini-split
A duct-free heat pump with one outdoor unit and one or more indoor heads — common for additions, upstairs zones, and homes without usable ducts.
Plenum
The sheet-metal box attached to the air handler or furnace that distributes supply air into the duct trunks.
Return air
Air pulled from the living space back to the system to be conditioned again.
Supply air
Conditioned air delivered from the system into rooms through supply registers.
Manual J
Industry load-calculation method used to size heating and cooling equipment for a specific home — not a rule-of-thumb tonnage guess.
Title 24
California Energy Code requirements that affect HVAC changeouts, including efficiency, controls, and documentation.
HERS testing
Home Energy Rating System field verification required on many California HVAC changeouts to confirm duct leakage, airflow, and refrigerant charge.
Balance point
Outdoor temperature where a heat pump's heat output equals the home's heat loss — below that, supplemental heat may be needed.
Variable-speed compressor
Compressor that modulates capacity instead of only on/off — better humidity control and steadier comfort.
Modulating gas valve
Furnace gas valve that varies flame output for finer temperature control and quieter operation.
Vapor compression cycle
The refrigeration cycle used by air conditioners and heat pumps: compress, condense, expand, evaporate.
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