Furnace repair or replace? How to decide

Every heating company will tell you to replace when they would rather sell a furnace, and to repair when they would rather not lose the call. The way through is a rule you can apply yourself, with both numbers in writing in front of you. Here is the one we use.

The rule

• Under about twelve years old, and the repair is less than a third of the cost of a replacement: repair it.
• Over fifteen years old, with a major failure such as a cracked heat exchanger, a failed control board, a seized blower or inducer motor: replace it.
• In between: get both prices in writing, add up what the furnace has cost in the last two winters, and decide with the gas saving in mind.

That is the whole rule. The rest of this guide is the detail that makes it work.

What repairs cost, and what a furnace costs

Typical Hamilton-area prices in 2026, parts and labour, after a diagnostic visit of $99 to $149 that is credited against the repair:

• Hot-surface igniter: $200 to $350
• Flame sensor: $150 to $250
• Capacitor: $150 to $250
• Pressure switch: $200 to $350
• Inducer motor: $450 to $800
• Blower motor: $500 to $950, more for a variable-speed ECM blower
• Control board: $450 to $850
• Gas valve: $400 to $700
• Heat exchanger: usually not worth quoting on a furnace over ten years old

A new furnace installed: about $4,500 to $6,000 for a 96 percent single-stage, $5,500 to $7,500 two-stage, $7,000 to $9,500 modulating. The full breakdown is in what a new furnace costs in Ontario.

Put the two side by side. A $300 igniter on a nine-year-old furnace is an easy repair. An $800 blower motor on a sixteen-year-old 80 percent furnace is a third of a new unit that will also cut the gas bill by a fifth; that is a replacement.

The faults that end the discussion

• A cracked heat exchanger. It can let combustion gases, including carbon monoxide, into the house air. No reputable technician will leave it running, and a new heat exchanger on an old furnace costs most of a new furnace.
• A failed control board on a furnace over fifteen, especially an older model where the board is hard to source.
• Repeated major repairs: if you have paid for two of the expensive items in the list above in two winters, the third is a down payment on a new furnace.

The case for repairing

A furnace is not a phone; it does not go out of date. A ten-year-old two-stage furnace with a dead igniter has another ten years in it. Plenty of furnaces we are called to replace just need a part, and we say so. If your contractor goes straight to a replacement quote without a diagnosis, get a second opinion.

The case for replacing on your own schedule

The worst time to buy a furnace is the February night it dies: no time to compare quotes, no rebate paperwork, and whatever the supplier has in stock. If your furnace is over fifteen, plan the replacement for a September or October you choose. Get the heat-loss calculation done, compare two or three quotes on the same basis, claim whatever rebate is open, and have the old furnace carried out on a mild day.

The gas bill in the maths

An 80 percent mid-efficiency furnace from the 1990s or 2000s uses roughly a fifth more gas than a 96 percent condensing unit. On a typical Hamilton heating bill that is a few hundred dollars a year. It does not pay for a furnace on its own, but added to avoided repairs over the next five winters it tips a lot of borderline cases toward replacement.

How to get both numbers

Book a repair visit. The technician diagnoses the fault, quotes the repair in writing, and if the furnace is in the grey zone gives you the replacement price for the correctly sized unit on the same visit, with the reasoning. No pressure either way; the decision is yours. Background on lifespan is in how long does a furnace last?