Repair or Replace Your Furnace

Furnaces follow a similar age × cost math as AC, with one important safety override: a cracked heat exchanger is always replacement, regardless of age.

The safety override

A cracked heat exchanger can leak CO into your living space. It's not repairable in the strict sense — the exchanger itself has to be replaced, and on furnaces over 8 years old that repair is 60-80% of a new furnace's cost. Always replace.

We inspect the exchanger on every fall tune-up.

The age × cost formula

Same $5,000 rule as AC: repair cost × age > $5,000 = replace. But note that furnaces last longer on average than ACs — 15-20 years vs. 12-15 years — so a 12-year-old furnace with a $500 repair is still worth fixing.

When it's clearly replace time

• Age 18+, ANY repair over $400.
• Cracked heat exchanger, any age past 8 years.
• Two or more failures in the same heating season.
• AFUE below 80% (old low-efficiency furnace burning gas you don't need to burn).
• AC is also 10+ years old — bundle the swap and save on install cost.

Key takeaway. Cracked heat exchanger = always replace. Otherwise use the same age × cost > $5,000 formula as AC, adjusted for the longer furnace lifespan.

Need a hand from a real Central Kansas technician? Call (785) 822-7550 and a Comfort Heating & Air tech will walk you through it — or request service online and we'll follow up the same business day.