Your furnace is acting up — but is it worth fixing, or time to replace? Here's how to make the call without getting pressured by a contractor with an incentive to sell you a new unit.
The 5,000 Rule
Multiply your furnace's age by the repair cost. If the result exceeds $5,000, replace it. Example: 18-year-old furnace needs a $350 repair. 18 × $350 = $6,300 — replace it. A 5-year-old furnace needing the same repair: 5 × $350 = $1,750 — fix it.
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7 Signs It's Time to Replace
1. Age over 15–20 years: The average furnace lasts 15–20 years. If yours is in this range and needs repairs, replacement math usually wins.
2. Repair costs exceed 50% of replacement: If a repair costs more than half what a new furnace would cost, replace it.
3. Rising heating bills: A furnace losing efficiency will show up in your gas bill before it shows up in a diagnostic. If your bills have climbed without a rate change, the furnace is working harder for the same heat.
4. Uneven heating: Cold spots or rooms that won't stay warm indicate a furnace that can no longer distribute heat properly — often a blower or heat exchanger issue.
5. Frequent cycling: If the furnace turns on and off more than normal, it's either oversized for your home or the heat exchanger is failing.
6. Yellow or flickering flame: A healthy furnace has a steady blue flame. Yellow, orange, or flickering flames can indicate carbon monoxide risk — this is a safety issue, not just an efficiency one.
7. Carbon monoxide detector trips: A cracked heat exchanger leaks CO into your living space. If your CO detector has gone off with the furnace running, replace the furnace immediately. Do not repair a cracked heat exchanger.
When Repair Makes Sense
Repair if: furnace is under 10 years old, repair costs less than $500, the issue is a simple part (ignitor, capacitor, thermocouple), and your heating bills haven't increased.
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