Furnaces in Calgary work hard. The heating season runs roughly eight months, and the temperature swings from Chinooks add cycling stress. Realistic life expectancy for a typical residential gas furnace in Calgary is 15 to 20 years for mid-efficiency units (now uncommon in newer homes) and 18 to 25 years for high-efficiency condensing units, with significant variation based on installation quality, maintenance history, and run-time.
A furnace at 15 years isn't automatically failing, but it is past the warranty window for parts and approaching the point where replacement makes more economic sense than repair. A furnace at 20 to 25 years should be considered end-of-life — not because it can't keep running, but because parts availability declines, efficiency lags significantly behind current units, and an unplanned mid-winter failure forces emergency replacement at premium pricing.
Replacement cost in Calgary for a standard high-efficiency single-stage unit installed runs $4,500 to $6,500 in 2026; two-stage and modulating units $6,500 to $9,000; combi-boiler conversions and complex installations higher. The price spread reflects equipment grade, installation complexity, ductwork modifications, and whether the existing venting, gas line, and electrical service are reusable.
During inspection, the inspector documents the unit's age (from the data plate or model and serial decode), operating condition at the time of inspection, heat exchanger condition where visible, vent and combustion-air arrangements, filter condition, and any signs of past service or recent repair. The inspector cannot fully evaluate the heat exchanger non-invasively — that requires service-tech access — but visible cracks, corrosion, or scorching are documented.
For buyers, the practical playbook: confirm age, factor a furnace nearing end-of-life into the offer, schedule service in the first season of ownership for any furnace over 12 years old (a service tech will identify any latent issues), and budget realistically. Don't assume a working furnace at age 18 will still be working at age 23 — plan and price replacement before the failure forces the timeline.
