A gas furnace in an Ontario house typically lasts 15 to 20 years. Some go 25 with good care and a bit of luck; some fail at 12 because they were oversized, starved of air or never serviced. Knowing roughly where yours is in that range, and the signs that it is near the end, lets you replace it on your schedule rather than in a January emergency.
Typical lifespans
- High-efficiency gas furnace: 15 to 20 years.
- Older mid-efficiency furnace: often 20 years or more, though anything from the 1990s is now well past its expected life.
- Central air conditioner: 12 to 18 years.
- Heat pump: 12 to 18 years; it works year-round, so it accumulates more running hours than an AC.
- Ductless mini-split: 12 to 20 years.
- Boiler: 15 to 20 years for a condensing boiler, 25 to 35 for a cast-iron one.
- Tank water heater: 8 to 12 years. Tankless: 15 to 20.
- Ductwork: decades; it rarely needs replacing, though it may need sealing or modifying.
How to find your furnace’s age
The rating plate inside the furnace door shows the model and serial number. Many manufacturers encode the year and month of manufacture in the serial number, and a quick search for the brand’s serial number format usually decodes it. Service stickers on the cabinet also tell you when it was last looked at. If the furnace has a standing pilot light and a metal flue going into a chimney, it is likely a mid-efficiency model from before about 1995.
What shortens a furnace’s life
- Oversizing: constant short cycles wear igniters, inducers and controls, and stress the heat exchanger.
- Dirty filters: restricted airflow makes the heat exchanger run hotter than it should.
- Undersized or blocked returns: common in older houses, with the same effect as a dirty filter.
- No maintenance: small faults turn into failures, and condensate problems corrode parts.
- Damp basements: rust attacks the cabinet, burners and controls.
- Renovation dust: drywall dust pulled through the furnace clogs the blower and coil.
Changing the filter on time, with the help of our guide on how often to change a furnace filter, and a yearly tune-up are the two things that most reliably add years.
Signs a furnace is near the end
- It is past 15 years and has needed repairs in each of the last two winters.
- A technician has found a cracked heat exchanger or serious corrosion.
- Some rooms never get warm even with clean filters and open registers.
- It makes new noises: banging on ignition, scraping, or a blower that labours.
- Gas bills have crept up without a change in how you use the house.
- The flame on an older furnace is yellow and wavering rather than blue.
- Parts for the model are hard to get, and repairs take days.
Air conditioners and heat pumps age differently
An air conditioner runs only through the summer, so its compressor collects relatively few hours a year. A heat pump runs in summer and through most of the winter, so it accumulates hours roughly twice as fast, which is why its life is quoted in a similar range despite more running. Outdoor units age from the outside too: bent fins, corroded coils and failing fan motors. Keeping the outdoor coil clean, the unit level and snow and ice cleared from around it does more for its life than anything else a homeowner can do.
The heat exchanger
The heat exchanger keeps combustion gases separate from the air that circulates through the house. Years of heating and cooling can crack it, especially in oversized or airflow-starved furnaces. A crack can let combustion gases, including carbon monoxide, into the house air. A certified technician who finds one will usually shut off the gas to the furnace, and on an older unit replacement is almost always the right call. Working carbon monoxide alarms outside each sleeping area are required by Ontario law in homes with fuel-burning appliances.
Repair or replace: a simple rule
A common rule of thumb multiplies the furnace’s age by the repair cost. If the result is more than the cost of a new furnace, replacement deserves a serious look. A $400 igniter on an 8-year-old furnace is clearly a repair. A $1,200 inducer motor on an 18-year-old one, with another repair last winter, points the other way. Price is not the only factor: comfort problems, noise and the chance to add a heat pump at the same time also count.
Replacing other parts of the system at the same time
If the furnace and air conditioner are both past 12 to 15 years, replacing them together usually costs less than two separate jobs, and the indoor coil and blower can be properly matched. It is also the natural moment to consider a heat pump in place of the AC. See the new furnace cost guide and heat pump vs furnace.
Planning ahead
If your furnace is 15 or older and still running, it is worth getting a replacement quote in spring or summer. You do not have to act on it, but you will know the price, the right size and the options, and you will not be choosing under pressure on the coldest night of the year.
Getting an honest assessment
Send one request for a tune-up or a repair and ask the technician to tell you plainly how much life they think the furnace has left. If replacement makes sense, they can quote it at the same visit. See furnace repair and furnace installation.
Questions people ask
How long does a furnace last in Ontario?
Usually 15 to 20 years for a modern high-efficiency gas furnace, longer with yearly maintenance and good airflow.
Should I replace a 20-year-old furnace that still works?
Not necessarily right away, but plan for it. Get a replacement quote now, keep up maintenance, and replace it before it fails in winter if repairs start adding up.
How can I tell how old my furnace is?
Look at the rating plate inside the door for the serial number. Most brands encode the manufacturing date in it. Old service stickers also help.
Does a cracked heat exchanger mean a new furnace?
On most furnaces, yes. Replacing the heat exchanger alone is expensive and rarely worth it unless the furnace is young and under warranty.