1. How old is it?
Most furnaces last roughly 15–20 years. A 7-year-old furnace with a bad part is almost always worth repairing. A 22-year-old furnace with a major failure often isn't.
2. What does the repair cost compared with its age?
A common rule of thumb: if the repair costs a large share of a new furnace and the unit is near the end of its life, replacement usually makes more sense. If it's a simple part on a healthy furnace, repair it.
3. Is it safe?
A cracked heat exchanger or a carbon monoxide problem changes everything. Safety comes first, and in that case we'll show you exactly what we found.
4. How often has it broken down?
One repair in five years is normal. Three service calls in one winter is a sign the furnace is wearing out.
5. Is the house comfortable?
Cold rooms, dry air and noisy operation can be fixed with a properly sized new system, sometimes paired with a heat pump for dual-fuel efficiency.
6. What rebates are available?
The federal tax credit ended after 2025, but utility rebates can take a real bite out of the cost. See 2026 rebates.
By John Greenley, owner of Greenley Heating & Cooling, Janesville, Iowa.