Repair or replace your furnace?
Repair a furnace under about 15 years old when the fix is small next to a new one. Lean toward replacing when it is 15 to 20 years or older, the repair runs past a quarter of the $4,000 to $6,500 a single-stage replacement costs, or a technician finds a cracked heat exchanger.
Carbon monoxide alarm sounding, or a smell of gas?
Leave the house now with everyone in it and call 911 or your gas utility's emergency line from outside. Do not touch switches or the furnace. The repair question can wait.
Repair or replace: the 2-minute check
Estimates update as you change the inputs. Nothing is sent anywhere.
Our read
Reasonable people would go either way. Get the repair price in writing and a replacement quote, then compare.
Carbon monoxide alarm or gas smell
- Get everyone out of the house, pets included.
- Do not touch light switches, the thermostat or anything that could spark.
- From outside, call 911 or your gas utility's emergency line.
- Stay out until the fire department or the utility says it is safe.
What tipped it
- Replace15 to 20 years old: the age range in which most gas furnaces get replaced.
- NoteThe repair (about $900) is 17% of a new single-stage furnace at $5,250: not decisive either way.
- ReplaceAge times repair price is $15,300, over the $5,000 rule-of-thumb line.
Rule of thumb: age × repair price
About 17 yrs × $900 = $15,300
Over $5,000, so the rule of thumb says replace. It is a heuristic, not a verdict.
Get the real number for your home: a free, no-obligation quote.
A rule-based check for planning, not a diagnosis. Only a TSSA-registered gas technician who has inspected your furnace can say what it needs. Prices are typical Ontario ranges before 13% HST.
On this page
How the check weighs your answers
Each answer adds points toward repairing or replacing, and the result lists every point that counted, so you see the reasoning, not just a score. Only a safety finding settles it alone. Repair quotes are weighed against what a new single-stage furnace typically costs, using current Ontario furnace prices.
| Factor | Leans repair | Leans replace |
|---|---|---|
| Age | Under 10 years | 15 to 20 years, more so past 20 |
| Repair price | Under 10% of a new furnace | A quarter or more of a new furnace |
| Recent repairs | None | Two or more in two years |
| Efficiency | High-efficiency, PVC venting | Mid-efficiency, about 80% |
| Comfort | Even heat, normal noise | Cold rooms, short cycling |
| Your plans | Moving within 3 years | Staying 7 years or more |
| Central AC | Under 12 years old | Also past 12: price both |
| Safety | No warnings | Cracked heat exchanger |
The $5,000 rule and its limits
A popular rule of thumb multiplies the furnace's age by the repair price: over $5,000, replace; under, repair. It is a quick sanity test, but it weighs only two things and leans hard on age.
- A 16-year-old furnace needing a $350 igniter scores $5,600, so the rule says replace. A cheap part on a furnace that otherwise heats well is usually worth fixing.
- A 6-year-old furnace needing an $800 control board scores $4,800, so the rule says repair. That is right, but check the parts warranty first: you may only owe labour.
It also ignores efficiency, comfort, safety and your plans, which is why the check scores them separately.
Typical furnace repair prices in Ontario
- Diagnostic or service call$100 to $200
- Hot surface igniter$250 to $450
- Flame sensor clean or replace$150 to $300
- Pressure switch$250 to $450
- Inducer motor$600 to $1,200
- Blower motor (PSC)$500 to $900
- Blower motor (ECM)$900 to $1,800
- Control board$500 to $1,100
- Gas valve$450 to $900
The cheap, common failures (igniter, flame sensor, pressure switch) are worth fixing at almost any age, and motors and control boards sit in the middle. A cracked heat exchanger is missing because it is usually replacement-level: the part may carry a long warranty, but the labour is heavy. Our furnace repair cost guide explains each repair.
What replacement costs, for comparison
Replacing a gas furnace in Ontario
Heating$4,000to$11,000
Typical installed price, Ontario 2026, all options shown
- Gas furnace, single-stage95 to 96% AFUE $4,000 to $6,500
- Gas furnace, two-stage96% AFUE, ECM blower $5,500 to $8,000
- Gas furnace, modulating97 to 98% AFUE, variable speed $7,000 to $11,000
Installed price in Ontario, before 13% HST ($4,520 to $12,430 with HST). Standard replacement in a detached home with usable ductwork and venting.
Most like-for-like replacements are single-stage furnaces. Leaving a mid-efficiency furnace for a condensing one adds venting: a PVC vent, a condensate drain and sometimes a chimney liner, because a gas water heater left alone in the old chimney may not draft safely ($300 to $1,500). If the AC is near the end too, both together typically run $8,000 to $15,000; see furnace and AC prices and the full furnace price guide.
Age, lifespan and efficiency
Most gas furnaces last about 15 to 20 years, longer with good care; see how long furnaces last for the warning signs. Age matters for what comes with it: older furnaces are more often mid-efficiency, parts get harder to find and each repair buys fewer years.
A mid-efficiency furnace turns about 80% of its gas into heat and a new one about 96%, roughly 17% less gas for the same warmth. The heating cost calculator puts a dollar figure on that for your house.
Get a replacement price before you approve the repair
A written replacement quote is the number to weigh a big repair against. Request one free, with no obligation, and compare.
Free, no obligation. About a minute to request.
Questions to ask before you decide
Ask the technician
- What exactly failed, and what caused it?
- Is the part under the manufacturer's warranty, and what will the labour cost?
- If you found a heat exchanger problem, can you show me the crack or the combustion test reading?
- Is the repair price written down, and does it include HST?
- What else on this furnace is likely to need work in the next two years?
- What is your TSSA registration number?
Gas work in Ontario must be done by a TSSA-registered contractor. You are free to get a second opinion before paying for a replacement, and regular furnace maintenance is the cheapest way to push the decision further out.
Questions people ask
Is it worth repairing a 15-year-old furnace?
Often, yes, if the repair is small. A $250 to $450 igniter or pressure switch on a furnace that heats well is usually worth doing. A blower motor, inducer or control board at $500 to $1,800 is toss-up territory at 15, and a second big repair within two years is a sensible point to replace.
How much does it cost to fix a cracked heat exchanger?
It is usually treated as replacement-level. The exchanger may be under a long manufacturer warranty, but the labour to swap it is extensive, so on an older furnace most owners put that money toward a new one at $4,000 to $6,500. Ask to see the evidence first.
Should I replace my furnace and air conditioner at the same time?
If the AC is over about 12 years old, price both. One job means one install and matched equipment, and a furnace and central AC together typically cost $8,000 to $15,000 in Ontario. A ducted heat pump is another way to cover heating and cooling with one system.
Can a technician make me replace my furnace?
No one can make you buy a furnace. But a gas technician who finds a hazardous condition, such as a cracked heat exchanger, can shut off the gas and tag the furnace as unsafe, and it should not be used until that is corrected. Ask to see the evidence, and get a second opinion from another TSSA-registered contractor if unsure.