Cardboard supply ducts in slab

Richard Moore · 06-06-2007, 09:16 PM

Ok...this is new for me. 1951 rambler, on a slab (which is rare around here). The furnace heat supply ducts appear to be no more than cardboard form tubes embedded in the slab and cut out at each register opening. No signs of any coating (asbestos, etc), just a lot of dust and dirt. Normal return ductwork, through the attic. Anyone seen this before?
Very good air flow at all registers, but it just don't seem right. Comments?

PS...the Pergo installed over the carpet was a nice touch (and a separate issue).

Finally, the Coleman furnace appeared to be brand, spanking new but the serial numbers don't seem to conform to anything I've seen on the various forums. Model FC85080A12DH11B, Serial # W0B7424908. Anyone able to shed some light there?

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**Rick Hurst** · 06-06-2007, 09:22 PM

Richard,

Looks like a real mess.

I've seen ducts in a slab, but only in Oklahoma and they were not cardboard.

Seem like termites would be hazardous to your ducts.

Pergo over shag? Who would have ever thought? I guess the extra cost for the padding just didn't make sense.

Richard Moore · 06-06-2007, 09:40 PM

"Seem like termites would be hazardous to your ducts."...

Probably not. I doubt that our subterranean or dampwood termites (our only common species) would find the conditions to their liking. Fire hazard maybe? But...if its been there for 50+ years?????

Yeah, the Pergo was amusing. Like a damn trampoline in all three bedrooms. And can you say moisture barrier? Clients already knew it had to be addressed.

**Thom Walker** · 06-06-2007, 10:43 PM

Richard,
Yup, confusing. Two things come to mind. Are you 100% sure that the ducts weren't asbestos? In the year you were dealing with it would have been perfect timing for it. It would also explain why, after 50 years in the ground they hadn't completely deteriorated.

I have attached some links and info. I suspect they may have made the V interchangable with a 5 in the model#. You might want to give Johnson controls a call to solve this. They own the Coleman Furnace name now.

Coleman had some serious heat exchanger problems in their manufactured home furnaces, but I don't know if it carried over to Home models. I do know that across the board, Coleman has had a reputation for handling recall notices poorly. This might be the perfect case for a referral.

Richard Moore · 06-07-2007, 12:22 AM

Hi Thom...yes 100% certain they were cardboard or paper, and didn't appear to have any lining or coating. Someone I trust on another forum says that they are common in his area (PA) in 50' and 60's slab homes, although usually damaged by now. I've posted another photo from a different register and you can see that these are actually in good shape (where visible), just ragged at some openings

As to the Coleman serial number...well...see the photo.

No installation or service stickers, but I'd eat my hat if this furnace had seen a single complete heating season, nevermind being 10 or more years old. Everthing inside and out was shiny new. Maybe they've just started a whole new numbering system? Thanks for trying though

**Thom Walker** · 06-07-2007, 05:41 AM

The model # is FC8S, not 5.

FC8S furnace

Hell, I'd contact them just to find out why they're screwing with the serial# system.

**Jim Robinson** · 06-07-2007, 05:57 AM

I see it all the time in one of the neighborhoods that I inspect. Most are fine, but a few have collapsed under ground. It's tough to tell what's going on without a camera snaked down through them. I don't know if they were supposed to be encased in concrete originally and weren't, or if they are just stuck down under the slab. I haven't excavated one of these houses yet, but would like to see one when it is cut open.

**wayne soper** · 06-07-2007, 08:42 AM

Seen it many times. Its a mess. The cardboard deteriorates and blocks the flow in areas. I guess you could snake flex duct through but the initial designer should be shot!