Glossary
HVAC terms in plain English.
Quick definitions of every acronym a contractor will throw at you. Each term is its own page so you can bookmark or share what's relevant.
Efficiency ratings
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AFUE
Annual Fuel Utilization Efficiency — how much of the fuel a gas furnace converts to usable heat over a year.
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SEER / SEER2
Seasonal Energy Efficiency Ratio — measures how efficient an AC is over a typical cooling season.
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HSPF
Heating Seasonal Performance Factor — how efficient a heat pump is at heating over a typical winter.
Refrigerants
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R-22 (Freon)
An older refrigerant phased out in 2020 — if your AC still uses it, replacement is in your near future.
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R-410A (Puron)
The dominant residential refrigerant since R-22 was phased out — itself being phased down through 2025–2030.
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R-454B
The new low-GWP refrigerant replacing R-410A in residential systems starting 2025.
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Refrigerant
The fluid that carries heat between indoor and outdoor coils in an AC or heat pump.
Components
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Compressor
The pump at the heart of every AC and heat pump — circulates refrigerant and does most of the work.
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Condenser
The outdoor coil that releases heat to the air — the radiator-like thing your outdoor AC unit is built around.
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Evaporator coil
The indoor coil where refrigerant absorbs heat from your home's air.
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Heat exchanger
The metal chamber inside a furnace where combustion gases transfer heat to indoor air — without mixing.
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Blower motor
The motor that drives the fan that pushes conditioned air through your ductwork.
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Flame sensor
A small metal rod that confirms the burner has lit so the gas valve stays open.
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Ignitor (Hot Surface Ignitor)
The component that lights the gas in modern furnaces — replaces the old standing pilot light.
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Condensate
The water that drips off your AC's evaporator coil. Has to go somewhere — usually a floor drain.
Airflow & ducts
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MERV
Minimum Efficiency Reporting Value — measures how small a particle a filter catches.
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HRV
Heat Recovery Ventilator — pulls in fresh outdoor air and recovers most of the heat from outgoing stale air.
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ERV
Energy Recovery Ventilator — like an HRV, but also transfers humidity between airstreams.
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Ductwork
The network of metal or flex tubes that carries conditioned air through your home.
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Static pressure
The 'resistance' your blower is fighting to push air through the ductwork. Too high = poor airflow + worn blower.
Controls
Ratings & sizing
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BTU
British Thermal Unit — the energy needed to raise 1 lb of water by 1°F. The unit HVAC sizing is measured in.
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Manual J
ACCA's industry-standard residential heat-loss/gain calculation — the right way to size HVAC equipment.
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Tonnage
AC capacity expressed in tons. 1 ton = 12,000 BTU/hr of cooling. Don't confuse with weight.
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Tons of cooling
Same as tonnage. 1 ton = 12,000 BTU/hr of cooling capacity.
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TSSA
Technical Standards and Safety Authority — Ontario's gas-and-fuels regulator. Required for all gas work.
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ECRA / ESA
Electrical Safety Authority of Ontario — required for electrical work, including HVAC electrical hookups.
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HVAC warranty
Most furnaces and ACs come with a 10-year parts warranty + 1-year labour. Heat exchangers often have lifetime coverage.
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BTU/hr
BTU per hour — the rate at which heating or cooling capacity is delivered.
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