Mornings are down around 46 now, and pretty soon you'll be running the furnace every day. First-run season is also when furnace problems tend to surface, the unit that limped along last winter finally acting up on a cold morning. If yours is getting up there in years and you're wondering whether to keep fixing it or replace it, here's how we'd walk you through the decision.
Same as we say about air conditioners: we install furnaces for a living, but we're not interested in selling you one you don't need. Sometimes a repair is clearly the right call, and we'll tell you when it is. But furnaces carry one factor air conditioners don't, and it can outweigh the money math entirely. We'll get to that.
How long does a furnace last?
Longer than your AC, usually. Most furnaces run 15 to 20 years, and a well-maintained one can push past that. So a furnace hitting 15 isn't automatically done the way a 15-year-old AC might be.
That said, once you're past about 15 years, every repair decision changes. You're weighing money against a unit that's closer to the end than the beginning, and the odds of the next failure climb each season.
If you haven’t maintained your furnace properly, you’ll be lucky to get 15 years out of a furnace problem free, expect large repair bills or replacement.
Is it worth repairing, or should I replace it?
The quick math we use is the same one we use for air conditioners. Multiply the age of the furnace by the cost of the repair. If that number is over about $3,000, replacement is usually the smarter money. A $500 repair on a 15-year-old furnace is $7,500, which means we recommend replacement. The other rule of thumb: if a single repair costs more than half the price of a new furnace, don't pour it into the old one.
But with a furnace, the math is only part of it, because a furnace burns fuel inside your home. That brings us to the part that matters most.
What are the signs a furnace is on its way out?
Some of these are about money. A few are about safety, and those get the final say.
The money signs:
- It's needed repairs two or three winters in a row.
- Your heating bills keep creeping up even though you haven't changed how you use it. Older furnaces lose efficiency every year.
- Some rooms never really get warm, and the furnace runs and runs trying to keep up.
The safety signs to pay attention to, which matter more:
- The burner flame is yellow or flickering instead of a steady blue. Blue means clean combustion. Yellow can mean it's burning incompletely, which can produce carbon monoxide.
- A cracked heat exchanger. This is the big one. The heat exchanger is the metal wall that keeps combustion gases, including carbon monoxide, separated from the air you breathe. When it cracks, that separation is gone. Repairing a heat exchanger often costs around $4,000, so in an older unit a crack usually means it's time to replace, and it's a safety matter, not just a comfort one. Carbon monoxide will kill you, so don’t take the chance.
- Your carbon monoxide detector goes off, or people get headaches or feel unwell when the heat runs. Treat that as urgent. Get everyone into fresh air and have it checked right away.
If a repair is minor and the furnace is otherwise healthy and safe, fix it. If the problem touches combustion or the heat exchanger on an aging unit, that's where replacement is often the honest answer.
Does my air conditioner factor into this?
It can. Your AC's indoor coil usually sits right beneath your furnace, and the two share the same blower. If your furnace is on its last legs and your AC is also getting old, replacing them together often costs less than doing two separate jobs a year or two apart. We wrote a whole separate post on when it makes sense to replace both at once, and it's worth a read if both of your units are up there in age.
When is repairing the right call?
Repair makes sense a lot of times. If your furnace is under about ten or twelve years old, the repair is straightforward, and it's been reliable, fix it and move on. A good furnace with one worn part doesn't need replacing. The honest version of this decision weighs age, safety, and the cost math together, not just whichever number is bigger, and a decent contractor will lay all of it out for you.
If however one part is worn with multiple parts showing signs of wear, issues, or are falling out of specification, replacement should be considered. That’s why we give options. We show what is wrong, and give you the price to fix it. Simple as that.
The short version
Furnaces generally last 15 to 20 years. When one needs a repair, weigh the age against the cost, and lean toward replacing if a fix runs more than half the price of new. But safety comes first: a yellow flame, a cracked heat exchanger, or a carbon monoxide alarm on an older furnace usually points to replacement no matter what the math says. Test your CO detectors either way.
If you're staring at a repair on an aging furnace and want a straight answer, we'll look at it and lay out both paths honestly, including telling you to keep the one you've got if that's the right move. We do free second opinions so if you don’t feel like you’re getting an honest experience from another company, we will let you know what we think. We're a family-run shop covering Nampa, Caldwell, Meridian, Boise, and beyond, and you can get on our schedule at (208) 969-8599.