- AFUE
- Annual fuel utilization efficiency: the share of a furnace's fuel turned into heat.
- AHRI certificate
- Confirms the rated efficiency of a specific matched indoor/outdoor combination.
- Air handler
- Indoor unit with a blower (and often a coil and heat strips) used with heat pumps and some ACs.
- Aux heat
- Backup heat that helps a heat pump automatically in cold weather.
- Btu/h
- British thermal units per hour; 12,000 Btu/h equals one ton of cooling.
- Capacitor
- Electrical component that helps motors and compressors start and run.
- Compressor
- The pump in the outdoor unit that moves refrigerant; the heart of an AC or heat pump.
- Condensate line
- Drain that carries water removed from the air away from the indoor coil.
- Contactor
- High-voltage relay that switches the outdoor unit on and off.
- Defrost cycle
- A heat pump briefly reversing to melt frost on its outdoor coil.
- Dual fuel
- A heat pump paired with a gas furnace that takes over in very cold weather.
- EER2
- Cooling efficiency at a single hot test condition.
- Evaporator coil
- Indoor coil where refrigerant absorbs heat from the air.
- Flame sensor
- Furnace safety device that confirms a flame is present.
- Heat exchanger
- Furnace component that transfers heat from combustion to the air without mixing them.
- HSPF2
- Seasonal heating efficiency rating for heat pumps.
- Manual J
- ACCA's room-by-room heating and cooling load calculation method.
- MERV
- Filter rating from 1 to 16; higher captures smaller particles but can restrict airflow.
- Mini-split
- Ductless system with an outdoor unit and one or more wall, ceiling or floor heads.
- R-410A / R-454B / R-32
- Refrigerants; R-454B and R-32 are lower-GWP replacements for R-410A in new equipment.
- Reversing valve
- Heat pump valve that switches between heating and cooling.
- SEER2
- Seasonal cooling efficiency under updated test conditions.
- Short cycling
- A system turning on and off too frequently.
- Ton
- A unit of cooling capacity equal to 12,000 Btu/h.
- Variable-speed
- Compressors or blowers that adjust output in small steps for comfort and efficiency.
Glossary
HVAC glossary
The words on your quote, decoded.
Keep reading
Buying guide
HVAC buying guide
Choosing a new AC, furnace or heat pump: system types, sizing, SEER2/HSPF2/AFUE ratings, brands, warranties and contractor quotes.
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Guide
SEER2, HSPF2 and regional efficiency standards
What SEER2, EER2 and HSPF2 ratings mean, the federal minimum efficiency standards for the North, Southeast and Southwest, and what ENERGY STAR requires.
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FAQ
Frequently asked questions
Answers to the most common questions about AC repair, furnaces, heat pumps, SEER2, refrigerants, filters and thermostat settings.
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