------Glossary
Every term on your quote, in plain English.
18 HVAC terms defined without jargon — so you can read an estimate and know exactly what you're looking at.
- AFUE
- Annual Fuel Utilization Efficiency — the percentage of fuel a furnace converts to usable heat over a season. An 80% AFUE furnace sends 20% up the flue.
- Air handler
- The indoor unit containing the blower and coil, used with heat pumps and electric systems in place of a furnace.
- Auxiliary heat
- Backup electric resistance heat that supplements a heat pump in cold weather or during recovery from a large setback. Effective but expensive to run.
- Condenser
- The outdoor unit, where heat collected from inside the house is released. Needs clear airflow on all sides to work properly.
- Dual fuel
- A heat pump paired with a gas furnace, switching between them based on outdoor temperature so the system uses whichever is more economical.
- Evaporator coil
- The indoor coil where refrigerant absorbs heat from household air. Matched to the outdoor unit — replacing one without the other compromises performance.
- Heat pump
- Equipment that moves heat rather than generating it, providing both heating and cooling by reversing the refrigerant cycle.
- HSPF2
- Heating Seasonal Performance Factor 2 — the heating-side efficiency rating for a heat pump, under the same updated test procedure as SEER2.
- Load calculation
- An engineering estimate of how much heating and cooling a specific house actually needs, based on size, insulation, windows and orientation. The correct basis for sizing equipment — square footage alone is not.
- MERV
- Minimum Efficiency Reporting Value — how much a filter captures. Higher MERV filters more but restricts airflow, so it must be matched to what the system can handle.
- Mini-split
- A ductless system pairing an outdoor unit with one or more indoor heads. Useful for additions, garages, bonus rooms, and homes without ductwork.
- Refrigerant
- The working fluid that carries heat through the system. It is not consumed — a system low on refrigerant has a leak, which should be found rather than simply topped off.
- SEER2
- Seasonal Energy Efficiency Ratio 2 — cooling efficiency measured under the current test procedure, which uses higher external static pressure to better reflect real ductwork. Higher is more efficient.
- Short cycling
- Turning on and off too frequently to complete a normal run cycle. Usually indicates oversizing, restricted airflow, or a control problem, and it wears equipment quickly.
- Static pressure
- Resistance to airflow within the duct system. Excessive static pressure reduces capacity and shortens equipment life — the ductwork equivalent of high blood pressure.
- Ton
- A unit of cooling capacity equal to 12,000 BTU per hour. Residential systems are commonly 1.5 to 5 tons. Bigger is not better — oversizing hurts both comfort and humidity control.
- Two-stage
- Equipment that runs at a lower capacity most of the time and a higher one when needed, giving steadier temperatures and better humidity control than single-stage.
- Variable-speed
- Equipment that continuously modulates output and blower speed, producing the quietest operation, the most consistent temperatures, and the best moisture removal.