The rule: the $5,000 Rule.
Multiply the repair quote by the age of your furnace in years. If the answer is over $5,000, replace the furnace. Under $5,000, repair it.
This works because it weighs both halves of the decision at once. A $600 repair on a 14-year-old furnace scores 8,400 — that is real money into a machine near the end of its life. The same $600 repair on a 5-year-old furnace scores 3,000, and it is obviously worth doing.
Furnaces last about 15 to 20 years. At 20 or older, replace it no matter what the repair costs — parts get scarce, efficiency is poor compared to modern units, and the next breakdown is always close. One more note: a cracked heat exchanger is an automatic replacement, no math needed, because of the carbon monoxide risk.
Quick answer
Repair quote × furnace age over $5,000 → replace it. Under $5,000 and furnace under 20 years → repair it. Cracked heat exchanger → replace it immediately.
Educational estimate only. Based on YOUR repair quote, cost of a new furnace installed, and age of your furnace in years you enter. Uses $5,000 Rule: Repair Quote × Furnace Age. Over $5,000 = replace, under $5,000 and furnace under 20 years = repair. 20+ years old = replace regardless. Cracked heat exchanger = replace immediately due to carbon monoxide risk. Not HVAC advice.
Disclaimer: Educational only, not professional advice. Get quotes from licensed, reputable contractors.
Frequently Asked Questions
What is the $5,000 rule for furnaces?
Multiply the repair quote by the age of your furnace in years. If the answer is over $5,000, replace the furnace. Under $5,000, repair it.
When should I replace instead of repairing?
If repair quote × furnace age is over $5,000, or the furnace is 20+ years old, replace it. Furnaces last about 15 to 20 years.
What if my heat exchanger is cracked?
A cracked heat exchanger is an automatic replacement, no math needed, because of the carbon monoxide risk.
When should I ignore this rule and talk to a professional?
This is educational only, not professional advice — get quotes from licensed, reputable contractors.
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