Definition — the four things a condensing furnace does differently
Sealed combustion: the burner draws its combustion air from a dedicated outdoor intake pipe, not from the room. This eliminates backdrafting risk and lets the furnace share tight mechanical rooms with other appliances safely.
Two heat exchangers: the primary exchanger extracts heat from the hot combustion gases, and a secondary exchanger cools those gases further until the water vapour condenses out — reclaiming latent heat that older furnaces sent up the chimney.
PVC venting: because the flue gases exit at roughly 40–60 °C (not the 300 °C of an atmospheric furnace), the vent can be PVC or CPVC instead of metal — and it can be routed through a side wall instead of a chimney.
Condensate drain: the acidic water pulled out of the flue gases has to go somewhere. Modern furnaces plumb this to a floor drain or condensate pump, sometimes through a neutralizer cartridge.
When to use it — sizing the furnace to your GTA home
Furnace sizing is a Manual J calculation, not a per-square-foot guess. Most GTA homes end up in the 60,000–100,000 BTU/h range, with older brick two-storeys and larger new-builds occasionally going higher.
Two-stage or modulating (variable-capacity) furnaces run at reduced output during shoulder-season weather — which gives longer, quieter cycles and better humidity control than a single-stage furnace short-cycling on a mild December day.
Failure modes — what goes wrong on a high-efficiency furnace
The most common in-season failure in Ontario is a plugged condensate line — the drain freezes at an exposed section, backs up, and trips the pressure switch. Second most common: a plugged flame sensor (a $10 part) that stops the furnace from proving flame within five seconds and locks out.
Cracked secondary heat exchangers are rare but serious — they're a warranty issue on any furnace within its 10–20 year exchanger warranty. Never run a furnace with a suspected cracked exchanger; call a TSSA-certified tech to inspect.
Proof — what AFUE, ENERGY STAR, and the EnerGuide label mean
AFUE (Annual Fuel Utilization Efficiency) is the percentage of a full winter's fuel input that becomes usable heat in your home. A 96% AFUE condensing furnace converts 96 cents of every fuel dollar into heat; the other 4% goes out the flue.
ENERGY STAR certification requires ≥ 95% AFUE for gas furnaces in Canada, plus an efficient blower motor (ECM). The Canadian EnerGuide label on the furnace itself confirms the AFUE the manufacturer submitted for testing.
Action — installing a condensing furnace safely
Every gas furnace install in Ontario requires a TSSA-certified gas technician and — in nearly every municipality — a mechanical permit and inspection. A proper install includes: correct venting slope and support, a P-trap and proper drain to the household plumbing, a combustion-air intake terminated per manufacturer clearances, and combustion-analyzer verification of the CO output at high fire.
Ask your installer for their TSSA licence details and confirm the municipal permit was pulled. Reputable installers welcome those questions. Contact Metroheat at (416) 283-5698 to schedule a heat-loss assessment.