How often should you inspect a heat exchanger?
Updated July 2026
Have the furnace heat exchanger inspected every year, folded into the fall tune-up, and more often once the furnace passes 15 years. The heat exchanger is the sealed metal wall that lets furnace heat reach your air while keeping combustion gases separate, and its one job is to keep carbon monoxide out of the house. A crack or rust-through breaches that wall, so this is a life-safety check rather than a comfort item. A tech inspects it with a mirror and light, and sometimes a combustion analyzer.
What changes the interval
| Your situation | Interval | Why |
|---|---|---|
| Furnace under 10 years | Yearly visual check | Cracks are rare, but the annual look sets a baseline |
| Furnace 15-20 years old | Yearly, with a combustion test | Metal fatigue from heat cycling makes cracks far likelier |
| Frequent short-cycling | Inspect now | Repeated rapid heating and cooling stresses the metal seams |
| CO alarm has sounded | Shut it off and inspect immediately | A cracked exchanger is a prime suspect for CO in the home |
| Visible rust, soot, or a wavering flame | Inspect now | These often accompany a compromised exchanger |
| Recently installed furnace | Yearly from year one | Warranty terms usually require documented annual service |
The cost of skipping it
What skipping it costs: a cracked heat exchanger can leak carbon monoxide, an odorless gas that causes headaches, nausea, and, at high enough exposure, death. That is the real stake, not the repair bill. Financially, a heat exchanger is rarely worth replacing on its own: at $1,500-3,000 for the part and labor, it often costs more than an aging furnace is worth, so a crack usually means a $4,000-8,000 furnace replacement instead. The annual inspection is bundled into a $100-250 tune-up. The full cost of ignoring a crack makes the yearly check an easy call.
How to do it (Pro inspection, part of a $100-250 tune-up)
- Schedule the furnace tune-up in early fall and ask specifically that the heat exchanger be inspected.
- Watch the burner flames: a steady blue flame is normal, while flames that flutter when the blower kicks on can signal a crack.
- Note any soot streaks, rust flakes, or a persistent chemical smell near the furnace and report them.
- Keep a working carbon monoxide alarm on every level and test it monthly as your backstop.
- If a CO alarm sounds or you feel headachy and nauseous indoors, shut the furnace off, ventilate, and get everyone outside.
Knowing the interval is the easy half. OnOtto reminds you at the right interval, and it won't let you snooze it into next year. Tasks persist until they're done, and completing heat exchanger inspections schedules the next one automatically.
Put this on autopilot, free for 30 daysFrequently asked questions
Can you inspect a heat exchanger yourself?
Not thoroughly. A homeowner can watch for warning signs, a wavering flame when the blower starts, soot, rust, or a repeated CO alarm, but the cracks that matter are often hairline and hidden inside the folds of the metal. Techs use an inspection mirror, a bright light, and sometimes a combustion analyzer or camera to find them. This is the one furnace check worth leaving to a pro, because the failure mode is carbon monoxide, not just lost heat.
Is it safe to run a furnace with a cracked heat exchanger?
No. Most manufacturers and gas utilities say a furnace with a confirmed crack should be shut down until it is repaired or replaced, because the crack can leak carbon monoxide into your living space. Some utilities will red-tag and disable the unit on the spot. If a tech condemns your exchanger, get a second opinion if you doubt it, but do not keep running it in the meantime; use space heaters safely instead.
How long does a heat exchanger last?
A well-made heat exchanger typically lasts the life of the furnace, roughly 15 to 20 years, and many carry a 20-year or lifetime parts warranty on the exchanger itself. Short-cycling, oversized units, chronically dirty filters, and closed-off registers all shorten it by stressing the metal with extra heat cycles. If you want the full picture, see how long a heat exchanger lasts and what accelerates the aging.
Should I repair or replace a cracked heat exchanger?
Usually replace the furnace. A new exchanger runs $1,500-3,000 installed once you count the labor to pull and rebuild the furnace, and if the unit is past 12-15 years that money is better put toward a new furnace with a fresh warranty. Replacing just the exchanger makes sense only on a young furnace still under parts warranty. The repair-or-replace breakdown walks through the age and cost thresholds.