Furnace smell

[JohnDar]

If the smell is coming from all the vents, it does sound like it originates at the furnace. A borescope inserted into the duct closest to the furnace (bedroom?) might reveal if there is some foreign object (or roasting rodent) in there.



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[TravelTiger]

If the smell is coming from all the vents, it does sound like it originates at the furnace. A borescope inserted into the duct closest to the furnace (bedroom?) might reveal if there is some foreign object (or roasting rodent) in there.



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Ew, I hope not! I don't think I can get a borescope to the furnace from the vents. It's a good 5 feet between them at a funky angle. But and Jim mentioned, I plan to take the ducts off and investigate.


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[TravelTiger]

Ok, removed vents and front and back cover, no evidence of anything. Still smells even when running with no vents.

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[danemayer]

Well, at least now you know how to get to the high-limit switch.

 

[TravelTiger]

Does it concern anyone that the top metal (heat exchanger?) section looks very burned?


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[RoadJunkie]

Good pics...thanks. I've always wondered what these things look like inside. I have not used my heater in almost a year, but last time I used it it was pretty rank. Funny, when I picked up the rig the heater had been on for quite a while, started by the dealership. When I drove it it a few hundred miles, and restarted the heater, the burning smell emerged. Waiting for the weather to be a little colder, then I'll try it before warranty expires.

 

[JohnDar]

Does it concern anyone that the top metal (heat exchanger?) section looks very burned?


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Looks like that corner is getting more heat than it should. What you may be smelling is overheated metal. Yes, it can definitely stink.

May be time to get it looked at professionally.


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[TravelTiger]

A couple more pics... is it odd this unit looks kind of "crammed" into place? I am beginning to wonder if this was not a "new" furnace.


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[danemayer]

A couple more pics... is it odd this unit looks kind of "crammed" into place? I am beginning to wonder if this was not a "new" furnace.


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The screws that hold the unit in on the sides can easily "stretch" the cage out of shape as they're tightened. The deformation at the top is less explainable. Overall it might suggest that the furnace was removed and reinstalled after the initial build. Does the cover plate on the outside show any signs of deformation around the screws?

On the discoloration of the upper combustion area, my initial reaction was that something on the surface might account for the discoloration as well as the smell. If it were an overtemp issue, the high limit switch should be cutting off power to the gas valve. You'd have a lot of cycling on and off because the overtemp condition would cut off heat before the thermostat was satisfied.

Do you have any ducts partially blocked to manage heat distribution?

 

[TravelTiger]

The screws that hold the unit in on the sides can easily "stretch" the cage out of shape as they're tightened. The deformation at the top is less explainable. Overall it might suggest that the furnace was removed and reinstalled after the initial build. Does the cover plate on the outside show any signs of deformation around the screws?

On the discoloration of the upper combustion area, my initial reaction was that something on the surface might account for the discoloration as well as the smell. If it were an overtemp issue, the high limit switch should be cutting off power to the gas valve. You'd have a lot of cycling on and off because the overtemp condition would cut off heat before the thermostat was satisfied.

Do you have any ducts partially blocked to manage heat distribution?

Dan, we added a louvered vent in the bathroom, but close it just slightly. I guess then yes, that might be partially blocked. If that were the cause I'd be very surprised, since the coach is not even 2 years old.

We used the heat very little in February/march of 2016. Then October2016-March2017. I know we had the smell in December, just not as bad. Now we have started to use the heat, and it seems to be worse.

When I watch u-tube videos of folks servicing furnaces, even old ones, they don't look as heat-tarnished as ours does.




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[danemayer]

Dan, we added a louvered vent in the bathroom, but close it just slightly. I guess then yes, that might be partially blocked. If that were the cause I'd be very surprised, since the coach is not even 2 years old.

We used the heat very little in February/march of 2016. Then October2016-March2017. I know we had the smell in December, just not as bad. Now we have started to use the heat, and it seems to be worse.

When I watch u-tube videos of folks servicing furnaces, even old ones, they don't look as heat-tarnished as ours does.




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I noticed you have four 4" ducts and one 2" duct. If you have an SF42, that just meets the minimum for installation requirements. Our LM has 5+1. So there's less duct volume on your furnace to start. Closing louvers may be taking you below the min. I don't think that would explain the smell, but it might explain the discoloration.

Instead of restricting airflow, maybe you could try putting a Tee into the ductwork and spilling hot air into the plumbing area and pass through storage.

 

[TravelTiger]

I noticed you have four 4" ducts and one 2" duct. If you have an SF42, that just meets the minimum for installation requirements. Our LM has 5+1. So there's less duct volume on your furnace to start. Closing louvers may be taking you below the min. I don't think that would explain the smell, but it might explain the discoloration.

Instead of restricting airflow, maybe you could try putting a Tee into the ductwork and spilling hot air into the plumbing area and pass through storage.

No, actually, there are five 4" ducts. Three off the back of the unit - Living Room, Kitchen, Hallway; then two more off the side that go to bathroom and bedroom, plus the 2" duct off the other side.

 

[JohnDar]

Yours is a two year old rig, you use the furnace infrequently and partially close one register. Mine is 9 years old, we’ve used the furnace considerably and have adjustable registers on all of the outlets, some of which are closed (like the bedroom). And our furnace does not stink up the place. We had it serviced last fall for a circuit board replacement and nothing was mentioned about heat damage to the furnace.


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[TravelTiger]

Yours is a two year old rig, you use the furnace infrequently and partially close one register. Mine is 9 years old, we’ve used the furnace considerably and have adjustable registers on all of the outlets, some of which are closed (like the bedroom). And our furnace does not stink up the place. We had it serviced last fall for a circuit board replacement and nothing was mentioned about heat damage to the furnace.


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I'm beginning to thing from my research that there is damage to the heat exchanger that we cannot see, or maybe some issue with the flame?

Another question I can't seem to find the answer to, can the high limit switch fail in the closed position and never shut off the furnace if it's getting too hot?


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[uncledon]

I'm beginning to thing from my research that there is damage to the heat exchanger that we cannot see, or maybe some issue with the flame?

Another question I can't seem to find the answer to, can the high limit switch fail in the closed position and never shut off the furnace if it's getting too hot?


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While reading all the posts I was wondering if there was an issue with your flame quality too. That might explain the disoloration of your heat exchanger.

Although I guess it's possible for those high limit switches to fail, they are like a fusible link that just melts when temperatures go to high. I haven't heard of failures.

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[JohnDar]

From the way it was installed (the damage in your photos), there may be a problem with the burner inside the heat exchanger. Like it got banged out of position. There are videos on bench testing RV furnaces, but it’s best done by a pro, methinks.


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[CoveredWagon]

I’d call customer service, send them the pictures and ask WT heck. Maybe when they see the damage to the furnace they might do something for you. Personally I’d be VERY VERY upset (********) to see a unit looking like yours no matter the reason, unless it had been in a wreck.

 

[danemayer]

Another question I can't seem to find the answer to, can the high limit switch fail in the closed position and never shut off the furnace if it's getting too hot?

Any switch can have a defect. And it could be that the switch is supposed to open at some temperature like 225 (F) but actually isn't opening until 250 (F), or not at all. Suburban docs say after opening, the switch should close again in about 5 minutes.

If a switch defect were combined with some other defect causing an elevated temperature, you might have an explanation for the discoloration. Still, that might leave a question as to what the smell is from.

Have you tried cleaning the exterior where it's discolored?

Suburban docs talk about using compressed air to clean debris out of the combustion chamber. I think you might do that from the exterior air intake. With the cabinet open the way you have it in the picture, that might be possible.

I'm not sure Suburban has support for end users, but you might try 423-775-2131 extension 7102. E-mail address: info1@suburbanmfg.com.

 

[rdfsnow]

I've read all the posts I can about furnace smell, and I'm not finding enough info.

We have a 2016 Big Country, purchased in January of 2016. We did run the furnace in early 2016, and the again in late 2016 and early 2017. Now it's late 2017, and we still have a bothersome odor from the furnace when it runs. I ran the unit a good couple of hours this week to start the season, so it was ready before it got colder, with windows open, hoping to rid us of the smell. The propane bottles are newly filled.

We fulltime, have induction cooktop and a LP fridge that we mostly run on electric, water heater runs on electric, so really the only time we use a propane is in the winter.

The smell is kind of a sweet/burnt smell, from all vents. Not a "dead" smell. Not a raw propane smell. The exhaust outside smells less offensive than inside. It starts off not too bad but longer the unit runs, the more bothersome it becomes to me, such that I feel like I might gag. Since the furnace tends to only run a short time and stop (a normal cycle), it's "tolerable" and I've assumed I'm just overly sensitive. But I certainly don't want to keep running it if there's an actual problem.

We have two CO detectors, and one is even directly over a heating vent. Neither has indicated an issue, and both have fresh batteries.

For a "regular Joe", what's the best course of action to find out if this is normal or not? I can call "the man" if I need to, but want to make sure I have exhausted the things we can look for ourselves, first.


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What I believe your smelling is lint and dust burning off the air side of the heat exchanger. This is normal after its been sitting awhile and not being used. It will burn off after a bit. These systems do not have a return air filter so the dust will lay on the exchanger.


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[JohnDar]

The discoloration on that exchanger is not soot and char, it’s severely overheated metal. If it were dust and lint burning, there would be smoke and a distinctly different smell.


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Looking again at the photo and the manual diagram for the furnace, the burner is in the bottom section of the heat exchanger. Outside, the air intake leads to the top section and the exhaust is the lower opening. Kinda brings me to think that maybe you had a large insect nest in that top section at the corner that was burning and causing the overheating of the metal. Any smoke and smell from that would be blown out the exhaust, past the burner assembly. What you were smelling was the metal cooking.

From the photo, it's obvious that the highest temperature was in the upper left corner (photo) and you have a decreasing heat gradient leading towards the right to where the two sections of the heat exchanger are joined. That would follow with the air induction path directing it that way.