BTU, AFUE, SEER, HSPF — the alphabet soup of heating and cooling, explained without the jargon. Written by a licensed Mississauga HVAC contractor for homeowners trying to make a real decision.
Buying an HVAC system is one of the bigger purchases a homeowner makes — but the industry runs on jargon that obscures real differences. Below: the terms we field the most questions about, answered straight.
AFUE measures how efficiently a furnace converts fuel into heat over a year. A 96% AFUE furnace turns 96% of the fuel it burns into heat for your home; the remaining 4% escapes through the exhaust. In Ontario, new gas furnaces must be at least 90% AFUE; high-efficiency models reach 96–98%.
A BTU is a measure of heat energy. One BTU is the energy needed to raise one pound of water by one degree Fahrenheit. Furnaces are rated in BTUs per hour — a typical Mississauga home needs a 60,000–100,000 BTU/hr furnace, sized to the home's heat loss, not its square footage.
SEER measures cooling efficiency over a season. Higher is better. As of 2023, the minimum SEER2 rating in Canada is 14.3 for central AC. High-efficiency systems run 18–24 SEER2 and use roughly 40% less power than minimum-rated units. SEER2 is the newer test standard; older equipment is rated in plain SEER (the conversion is approximately SEER2 = SEER × 0.95).
A heat pump moves heat instead of generating it — it pulls heat out of outdoor air and pumps it inside in winter, and reverses in summer to act as an air conditioner. Modern cold-climate heat pumps work down to around -25°C, making them viable as primary heating in southern Ontario. They typically deliver 2–4 units of heat for every unit of electricity used (the "coefficient of performance" or COP).
A ductless mini-split is a heat pump with a small outdoor compressor connected to one or more wall-mounted indoor units, with no ductwork between them. Ideal for additions, finished basements, garages, condos, or rooms that the central system can't reach. Each indoor unit can be controlled independently.
Single-stage furnaces run at one fixed output — full blast or off. Two-stage furnaces have a high and a low setting, running on low most of the time for quieter, more even heating. Modulating furnaces (also called variable-capacity) adjust output continuously between roughly 35% and 100%, providing the most consistent temperatures and lowest operating cost.
HSPF measures how efficiently a heat pump heats over a season. Higher is better. Modern cold-climate heat pumps run HSPF 9–13. The newer HSPF2 standard uses slightly different test conditions; an HSPF2 of 8 is roughly equivalent to HSPF 9.
Enbridge's Home Efficiency Rebate Plus (HER+) is a rebate program for Ontario homeowners who upgrade insulation, windows, and heating systems. Heat-pump installations can qualify for substantial rebates, often over $5,000 when stacked with the federal Canada Greener Homes Grant. A pre-retrofit and post-retrofit energy assessment by a registered advisor is required.
The Canada Greener Homes Grant offers federal funding for retrofits that improve home energy efficiency — including up to $5,000 for heat pumps and other measures. As of 2026, the grant has been extended in some provinces but program details change; check natural-resources.canada.ca for current rules before booking work.
TSSA G2 is an Ontario gas technician licence issued by the Technical Standards and Safety Authority. A G2 licence-holder may install, service, and repair gas appliances rated up to 400,000 BTU/hr — covering all residential and most light-commercial work. G1 is the higher tier with no BTU limit. Anyone working on natural-gas appliances in Ontario must hold one or the other.
Short cycling is when a furnace or AC turns on and off too frequently — usually for less than 10 minutes per cycle. Common causes: oversized equipment, a clogged air filter, a dirty flame sensor, a failing limit switch, or a leaking refrigerant line. It wears out the system fast and drives up energy bills, so it's worth diagnosing quickly.
A humidifier adds moisture to your home's air — usually by attaching to the furnace and pulling water from your plumbing. Ontario winters routinely drop indoor humidity below 20%, which causes static, dry skin, cracked wood floors, and respiratory irritation. Most homes benefit from one; bypass and steam types are the common options.
A smart thermostat is a Wi-Fi-connected thermostat that learns your schedule, can be controlled remotely, and integrates with heat pumps and zoned systems. Common models in Canada: Ecobee, Google Nest, and Honeywell Lyric. Most smart thermostats save 8–15% on heating and cooling costs through smarter scheduling alone.
For a standard 1-inch pleated furnace filter: change every 1–3 months. For a 4–5 inch media filter: every 6–12 months. Check more often if you have pets, allergies, or recent renovations. A clogged filter is the single most common cause of furnace short-cycling and AC freeze-ups.
Ductwork is the network of metal or flexible tubes that carries heated and cooled air from your furnace or AC to each room. Poorly designed or leaky ductwork can waste 20–30% of heating and cooling output and create rooms that are too hot or too cold. Sealing and insulating ducts is one of the higher-ROI HVAC improvements.
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