Cracked furnace exhaust pipe

[Scamper Jim]

This post is about the potentially lethal problem I found with the cracked furnace exhaust pipe on my Suburban furnace in my '83 Scamp. I found the crack while examining the furnace for the causes of noises and screeches when the furnace ran. I described that full process in the threads "Fixing noisy Suburban Furnace" as well as in "Quieting the Suburban Furnace". I am addressing only the cracked exhaust pipe here. Photos of the cracked and broken exhaust pipe are below.

Because the furnace burner metal is heated and cooled thousands of times over its life, it can become brittle or weak with age. While wiggling parts to locate the source of squeaks and screeches, I was surprised to find the crack in the exhaust pipe where it connects at the back of the heating unit. After taking the photo of the crack, I twisted the pipe with my hand and it broke off fully. In fact, the only thing still holding the exhaust pipe on my older furnace was a small bit of metal that is bent up. It can be seen in the photo. A few more times down the road and the pipe would probably have broken off on its own.

It’s amazing to me that the furnace is supported on the back end only by the exhaust and air intake pipes inserted within and hanging from the pipes that are secured to and enter from the outside of the camper. There is no other hanger or bracket system holding it. All of the weight on the back end is on those pipes. When pulling the trailer and hitting bumps, the furnace and pipes are jarred and eventually there can be metal fatigue and hence cracks and breaks in the pipes. This would lead to exhaust gases being released at the back of the furnace within the camper. In fact, it would be possible for the exhaust pipe to be fully broken off and not know it because the air intake pipe would carry the remaining full weight of the furnace with no indication of the problem.

The precaution I took to prevent a broken pipe in the future, was that when I re-installed the furnace I put a piece of carpeting on the top of the wheel well to support the back end of the furnace and take the load and jarring off the pipes. I later wedged a piece of tapered wooden shingle between the wheel well and bottom of the furnace to keep the furnace from sagging into the carpet over time and the problem occurring again.

Hope this is of use to others.

[Darrell in Al]

Thanks, I'll try to keep it in mind as a check.

[Carol H]

Jim, thanks for sharing this.

You have highlighted the need for people to be very careful about using old furnaces and the need for them to be very carefully checked over before using. Unfortunately cracked & or rusted out exhaust pipes are pretty common issues.

[Darwin Maring]

Just another justification to having a Carbon Monoxide detector in the egg. We have 2 of them. I don't think you can B 2 cautious when it comes to fire, propane gas and Monoxide.

[Carol H]

If you have Carbon Monoxide detector its good to check them once a year - impractical the expiry date on it - most are only good for 4 or 5 years.

[Jared J]

Mine sits on a piece of wood.