HVAC terms in plain English.

AFUE

Annual Fuel Utilization Efficiency — how much of the fuel a gas furnace converts to usable heat over a year.

SEER / SEER2

Seasonal Energy Efficiency Ratio — measures how efficient an AC is over a typical cooling season.

HSPF

Heating Seasonal Performance Factor — how efficient a heat pump is at heating over a typical winter.

R-22 (Freon)

An older refrigerant phased out in 2020 — if your AC still uses it, replacement is in your near future.

R-410A (Puron)

The dominant residential refrigerant since R-22 was phased out — itself being phased down through 2025–2030.

R-454B

The new low-GWP refrigerant replacing R-410A in residential systems starting 2025.

Refrigerant

The fluid that carries heat between indoor and outdoor coils in an AC or heat pump.

Compressor

The pump at the heart of every AC and heat pump — circulates refrigerant and does most of the work.

Condenser

The outdoor coil that releases heat to the air — the radiator-like thing your outdoor AC unit is built around.

Evaporator coil

The indoor coil where refrigerant absorbs heat from your home's air.

Heat exchanger

The metal chamber inside a furnace where combustion gases transfer heat to indoor air — without mixing.

Blower motor

The motor that drives the fan that pushes conditioned air through your ductwork.

Flame sensor

A small metal rod that confirms the burner has lit so the gas valve stays open.

Ignitor (Hot Surface Ignitor)

The component that lights the gas in modern furnaces — replaces the old standing pilot light.

Condensate

The water that drips off your AC's evaporator coil. Has to go somewhere — usually a floor drain.

MERV

Minimum Efficiency Reporting Value — measures how small a particle a filter catches.

HRV

Heat Recovery Ventilator — pulls in fresh outdoor air and recovers most of the heat from outgoing stale air.

ERV

Energy Recovery Ventilator — like an HRV, but also transfers humidity between airstreams.

Ductwork

The network of metal or flex tubes that carries conditioned air through your home.

Static pressure

The 'resistance' your blower is fighting to push air through the ductwork. Too high = poor airflow + worn blower.

Thermostat

The device that tells your HVAC system when to run.

Zoning

Splitting your house into separate temperature zones, each with its own thermostat and dampers.

BTU

British Thermal Unit — the energy needed to raise 1 lb of water by 1°F. The unit HVAC sizing is measured in.

Manual J

ACCA's industry-standard residential heat-loss/gain calculation — the right way to size HVAC equipment.

Tonnage

AC capacity expressed in tons. 1 ton = 12,000 BTU/hr of cooling. Don't confuse with weight.

Tons of cooling

Same as tonnage. 1 ton = 12,000 BTU/hr of cooling capacity.

TSSA

Technical Standards and Safety Authority — Ontario's gas-and-fuels regulator. Required for all gas work.

ECRA / ESA

Electrical Safety Authority of Ontario — required for electrical work, including HVAC electrical hookups.

HVAC warranty

Most furnaces and ACs come with a 10-year parts warranty + 1-year labour. Heat exchangers often have lifetime coverage.

BTU/hr

BTU per hour — the rate at which heating or cooling capacity is delivered.