Repair or Replace the Furnace? The Honest Math
This question usually arrives at the worst moment — cold house, tech in the basement, quote in hand. Here's the framework to think it through before that moment, or standing in it.
Safety first, every page: a cracked heat exchanger or any gas leak is not a "think it over" item. Smell gas: leave and call the gas company from outside.
The age bands
Gas furnaces typically live 15–20 years; well-maintained ones stretch longer, neglected ones less.
- Under 10 years: repair, almost always. Most big parts may still be under manufacturer warranty (check — parts warranties of 10 years are common, though labor isn't covered).
- 10–15 years: judgment territory. Small repairs, yes. Four-figure repairs deserve the math below.
- 15+ years: any major repair is really a down payment on the next failure. Get a replacement quote alongside the repair quote and compare with clear eyes.
The 50% rule
If the repair costs more than half the price of a comparable new furnace, replacement usually wins — especially past age 12. A $900 control board in a 16-year-old furnace is $900 toward equipment that's still 16 years old everywhere else.
Repairs that usually mean "replace"
- Cracked heat exchanger — this is the big one. It can leak combustion gases (including carbon monoxide) into your air. The repair is so expensive that on an older furnace it's effectively a replacement decision. It's also the diagnosis most worth a second opinion, because it's both genuinely serious AND occasionally used as a scare tactic. A legit tech can show you evidence: a camera photo of the crack, or a combustion analyzer reading — not just the words "it's cracked."
- Blower motor + board + anything else at once on a 15+ furnace — stacked repairs are the furnace telling you where this is going.
Repairs that usually mean "repair"
Ignitors, flame sensors, capacitors, pressure switches, thermostats — routine parts, modest money, no reason to replace a working system over them at any age.
The bubble-decision checklist
Standing there with a quote? Ask: the furnace's age (serial number decodes it; the tech knows), the repair price vs. half a replacement, whether the part's warrantied, and what ELSE is near failure. Then — for anything over $1,500 — sleep on it if the weather allows. Urgency is a sales tool; space heaters exist.
Related symptoms
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