Is this deadly problem lurking in your basement?
We were called to service a customer's 10-year-old furnace, and during a routine maintenance visit we found a very serious problem: a cracked heat exchanger. We shut the heat off right away, and the furnace had to be replaced.
Most people wouldn't expect this on a furnace that's only 10 years old. That's exactly why we're sharing it.
What is a heat exchanger?
The heat exchanger is the part of a gas furnace that keeps the flame and exhaust gases separate from the air that's blown through your home. The burners heat it up, and your furnace fan pushes household air across the outside of it. The exhaust stays inside and goes out the vent.
Why is a crack dangerous?
A crack can let the products of combustion, including carbon monoxide (CO), escape into the air that circulates through your house. CO has no colour and no smell. That's why a furnace with a cracked heat exchanger is considered unsafe and should not be run. Learn more in our post on carbon monoxide.
Listen as Bill Salmon explains what we are seeing in these photos:
Bill is asked what might have caused this problem:
Bill Salmon explains what we found
"That's a picture of the heat exchanger from, believe it or not, a 10-year-old furnace. We found it while doing maintenance for a customer, and obviously that's an unsafe condition. A crack in the heat exchanger can let the products of combustion get into the air that's moved throughout the house. At least three of the chambers had cracks, some of them two. No one would ever think that would happen on a 10-year-old furnace.
We see this all the time. People think they've got newer equipment, so they don't need to have it looked at, and they're safe. I'd say don't count on that. If you aren't going to do it every year, at least do it every other year. Have somebody check it.
We're not trying to scare people. Does every 10-year-old furnace have a failed heat exchanger? No. But things can go wrong, and if it's in your home, how would you know?"
Bill Salmon, Salmon Plumbing & Heating
What causes a heat exchanger to crack?
"Equipment just doesn't last as long as it used to. I've said that equipment lasts somewhere between 15 and 20 years, and a lot of your listeners have 30-year-old furnaces and will say, 'That guy's nuts.' I agree. The old stuff was very thick plate and was going to last forever, but you can't get parts.
This was probably just bad metal, metal fatigue. If you don't clean your filters, the furnace gets very hot. It overheats and cools, overheats and cools, and that might have led to it. But I don't want to say that, because I don't know. What I would say is that it can happen. So pay attention, and have a professional look at your equipment."
Bill Salmon
- Metal fatigue. The heat exchanger heats up and cools down every time the furnace runs. Over the years, that wears on the metal.
- Overheating from poor airflow. A dirty filter or blocked vents make the furnace run hotter than it should. See changing your furnace filters.
- Age. Today's furnaces are built lighter than the old ones, so they don't last as long.
How we found it
You usually can't see a crack. During maintenance, the technician looks into the heat exchanger with a mirror. But the bigger clue is a combustion test that measures how much carbon monoxide the furnace produces when it burns. Bill explains:
"It was producing excessive levels. That tells us the flame is being disturbed by a leak in the system, and that's how we found it."
That's a check you can't do yourself, and it's a big reason a yearly maintenance visit matters.
Warning signs to watch for
A cracked heat exchanger is often hidden inside the furnace, so you may not notice anything at all. Call a technician if you see:- Your carbon monoxide alarm going off
- Soot or rust around the furnace or burners
- A yellow, flickering or lazy burner flame instead of a steady blue one
- An unusual smell when the furnace runs
- The furnace shutting off and restarting over and over
- Headaches, nausea or tiredness in the household that ease when you're away from home
If your CO alarm goes off, get everyone outside and call 911 first.
How to protect your family
- Book a furnace check every year. A technician can inspect the heat exchanger, burners and venting before problems become dangerous. See Do I Need Annual Furnace Maintenance?
- Have working CO alarms. In Ontario, homes with a fuel-burning appliance (like a gas furnace or water heater), a fireplace or an attached garage need a CO alarm outside every sleeping area. Test them monthly and replace them as the manufacturer recommends.
- Change your filter regularly so the furnace doesn't overheat.
- Don't assume newer means safe. As Bill says, a 10-year-old furnace can still have problems.
Serving London since 1955. Questions about your furnace? Call (519) 451-8910 (24-hour emergency service) or request a quote.
