There is no diagnosis in this trade that changes a homeowner's day faster than "your heat exchanger is cracked." It stops being a repair conversation and becomes a safety conversation, usually in February, usually with a red tag on the furnace and the gas shut off at the valve.
It also happens to be the diagnosis homeowners trust least — because it is the one that always ends in a big number. That skepticism is healthy. So here is the honest version: what the part does, why it can't be patched, how to confirm the crack is real, and what the three actual paths forward cost in Puget Sound.
What the heat exchanger actually does
In a gas furnace, combustion never touches the air you breathe. Gas burns inside a sealed steel chamber — the heat exchanger. Your blower pushes household air across the outside of that steel, picks up the heat, and sends it down the ducts. The exhaust gases stay inside the metal and leave through the flue.
That steel is the wall between combustion byproducts and your living room. It gets heated to several hundred degrees and cooled again every single cycle, for fifteen or twenty years. Metal fatigue eventually wins. Add a furnace that short-cycles, runs with a filter that has been clogged since the Obama administration, or was oversized from day one, and it wins sooner.
When that wall opens up, exhaust — including carbon monoxide — can mix into the supply air. That is the entire reason this is treated differently from any other furnace repair.
Why "repair" isn't really on the table
People ask whether the crack can be welded, sealed, or epoxied. The answer is no, and it isn't a manufacturer upsell.
- The steel is thin and stamped, engineered to flex as it heats. A weld creates a rigid spot that cracks again next to the weld.
- No manufacturer approves a field repair, so any patched exchanger voids the warranty on the whole appliance.
- Where there is one crack from thermal fatigue, there is usually stress everywhere else in the same assembly.
So "repair" in practice means replacing the entire heat exchanger assembly — the single most labor-intensive job inside a furnace. Routine furnace repairs in our market run $150 to $1,500 typical. A heat exchanger replacement lives at the very top of that range and frequently above it, because the technician has to strip the furnace down to the cabinet: burners, gas valve, manifold, blower, controls, and wiring all come out, the new exchanger goes in, and everything goes back together and gets combustion-tested.
The carbon monoxide part
Carbon monoxide is odorless. Symptoms — headaches, nausea, drowsiness that improves when you leave the house — look like a winter cold. If a crack has been confirmed on your furnace, shut it off at the service switch or breaker, don't run it "just at night," and make sure you have working CO alarms on every level. Our design temperatures here run 17°F to 29°F depending on the city. A few days on space heaters is survivable. The alternative is not worth gambling on.
Make sure the crack is real first
A cracked exchanger is a legitimate finding. It is also, occasionally, a shortcut to a sale. You are entitled to proof before you spend five figures.
What a real diagnosis looks like
- Visual or borescope evidence. A camera down into the exchanger cells, with a photo or video you get to see.
- Combustion analysis. A meter in the flue reading CO levels and combustion efficiency, before and after the blower engages.
- Flame behavior. Burner flames that roll, distort, or shift the moment the blower starts often mean air is leaking through the exchanger.
- Age and history that fit. A 22-year-old furnace with rust scale and soot streaking is a plausible candidate. A six-year-old furnace usually isn't, unless something else is wrong.
If a contractor red-tags a furnace without showing you any of the above, get a second opinion. Any honest shop will tell you the same thing — including us. We would rather lose a job than sell a furnace somebody didn't need.
Option 1 — replace the exchanger
This makes sense in a narrow set of cases:
- The furnace is roughly 10 years old or younger.
- You have proof of the manufacturer parts warranty — heat exchangers often carry 20-year or lifetime coverage to the original registered owner.
- The rest of the furnace is healthy: good blower motor, clean burners, sound control board.
- The install itself was done well and the ductwork isn't the underlying cause.
Even with the part covered, you pay labor, and labor is the bigger half. Get that number in writing and put it next to a replacement quote before you decide.
Option 2 — replace the furnace
Once a furnace is past about 12 years, spending most of a new furnace's price to rebuild the core of an old one is a bad trade. You end up with a new exchanger inside an aging cabinet with an aging blower, an aging inducer motor, and an aging board — and no meaningful warranty on any of it.
What replacement costs in Washington
| Job | Standard market | Affluent market |
|---|---|---|
| JobGas furnace replacement | Standard market$4,000 – $8,000 | Affluent market$5,000 – $10,000 |
| JobFurnace + central AC together | Standard market$10,000 – $16,000 | Affluent market$11,500 – $19,200 |
| JobDucted heat pump | Standard market$12,000 – $18,000 | Affluent market$13,800 – $24,300 |
Most furnace replacements are finished in one day, and every install we do carries a 10-year parts and labor warranty. Permits get pulled on every job.
Option 3 — the one worth pricing before you sign
A dead furnace is the cheapest moment you will ever have to reconsider what heats your house. The ductwork is already there. The crew is already coming.
A ducted heat pump replaces heating and air conditioning in one system, and unlike a furnace it can qualify for PSE rebate money — up to $4,400 toward a qualifying heat pump when it replaces an existing electric or fossil-fuel system, with the exact amount depending on what you're replacing and what you install. Programs change, so we confirm your current eligibility and handle the paperwork. From April 2, 2026, PSE rebates require a PSE-certified installer; Varsity is one. The federal 25C tax credit ended December 31, 2025 and does not apply to any 2026 install.
If your existing furnace was young and healthy, we'd tell you to keep it as backup in a hybrid setup. With a cracked exchanger, that furnace isn't backup — it's scrap. That changes the math, and it's laid out in detail in our posts on replacing a gas furnace with a heat pump and the heat pump vs. gas furnace comparison.
Sometimes a straight furnace swap is still the right answer — tight budget, no interest in cooling, gas service you're happy with. We'll say so.
What to do tonight
- Turn the furnace off at the service switch or breaker. Don't run it.
- Test or install carbon monoxide alarms on every floor.
- Ask for the evidence — photos, combustion readings, the technician's notes.
- Find your furnace paperwork and check the model, serial, and registration date for warranty coverage.
- Get two written quotes that include exchanger replacement and full replacement, so you're comparing real numbers instead of pressure.
Want a ballpark before anyone visits? The instant estimate tool gives you Good, Better, and Best starting prices in about 60 seconds. For a firm number, we come out, measure, run the load calculation, and put options in writing.
Talk to someone who will show you the crack
We're owner-operated out of Federal Way and we serve 45 cities across King, Pierce, Thurston, and the edge of Kitsap County. No door knockers, no manufactured urgency, no franchise call center — just a written proposal with tiers and an honest read on whether your furnace is finished.
Request an estimate or call (253) 785-4622, Monday through Friday, 8 a.m. to 6 p.m.