The rule of thumb
Multiply the furnace's age by the repair quote. Over about $5,000, a new furnace is usually the better buy. Under $3,500, fix it. In between, get a replacement price before you approve the repair. ENERGY STAR suggests considering a new furnace once it's past 15 years old.
Two things bend the rule. A furnace ten years old or younger may still have the part under warranty, so check before you pay. The calculator calls those close instead of replace. And a furnace on its third repair in two winters is usually worth replacing.
What each failure usually means
- Igniter. It wears out, and swapping it is quick and cheap at almost any age.
- Flame sensor. It often only needs a cleaning.
- Inducer motor. It's a mid-size repair, so the furnace's age decides it.
- Control board. On an older furnace, ask whether the quote is for the original board or a universal one.
- Blower motor. A variable-speed motor costs far more to replace.
- Gas valve. It's a standard part and worth fixing on a furnace with years left.
A cracked heat exchanger
The heat exchanger keeps the flame and its exhaust out of the air in your house. A crack can let carbon monoxide through, so the repair price doesn't decide this one. If a technician or Xcel shut the furnace off, leave it off.
On a young furnace, ask about the heat exchanger warranty first. It usually runs longer than the parts warranty, though labor is often extra. Past its mid-teens, replacing it is the usual answer. Test your CO alarms and keep space heaters three feet from anything that can burn.
A gas smell or a CO alarm
If you smell gas, Xcel Energy says to leave right away and call 911, then Xcel at 800-895-2999, from outside. Don't flip switches or open the garage door on the way out. If a CO alarm goes off, the CPSC says to get everyone into fresh air, call 911 and stay out until responders say it's safe.
Check your furnace
Run the repair-or-replace calculator or see typical repair prices by part. If it leans toward replacing, send photos of the furnace and the repair ticket and we'll send back a written replacement price.
Common questions
Is the $5,000 rule exact?
No. It's a rule of thumb for a quick first call. A young furnace with a parts warranty, or an old one on its third repair in two winters, can change the answer.
Can I run a furnace with a cracked heat exchanger until I decide?
No. If a technician found a crack and shut the furnace off, leave it off. A crack can let carbon monoxide into the house.