Help problem with slab duct work

rhusdermNovember 24, 2010

I live in a 1950's house. The house is built on a slab without a basement. The Kitchen floor is brick over slab. The Duct work is under the slab and consists of terracotta pipes, that are at least a foot under the kitchen floor. I noticed At one union the pipe has settled about 2 inches, from freeze thaw I assume. This misalignment is large enough to allow the pea gravel to spill in.

I would like to avoid digging up the kitchen floor or ground outside the kitchen. Is there any way to repair the ducting.

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Run it through the attic like most houses on slab. I've never even heard of running HVAC through a slab or in terra cotta. It's a bad idea for both. AC through an uninsulated slab will have condensation build up and moisture tends to grow molds. Yech. You've probably got a petri dish under your home. Have a HVAC guy redo it all in insulated duct in your attic space.

    Bookmark   November 25, 2010 at 11:50PM
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Today's underground duct is a insulated, epoxy coated galvanized spiral pipe.

Look into pipe relining usually done in plumbing but it can be applied to seal up that area.

    Bookmark   November 26, 2010 at 12:14AM
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The pipe relining sounds like a good thing to look into, I've often wondered how effective it would be for drainpipes, but for hvac it ought to be ok, the stresses and issues if they leak shouldn't be such a big deal. You might even be able to slide some aluminium flex ducting in there I suppose, just to cover where it's slipped. I'd be more concerned about what's happening under the slab to cause it. You may want to test for mould overall.

If there's no insulation under the slab ( assume there isn't since you mention pea gravel, the air going through those 'ducts' will be attempting to heat all the ground underneath. Nice for warm feet I suppose.

Are you seeing the disconnected duct from the register? Interesting concept, anyway.

Certainly stuff can be rerouted through the attic, not cheaply, but in some cases there may be fire issues to address.

    Bookmark   November 27, 2010 at 7:50PM
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Thanks for the feedback. Unfortunately our house has no attic. We have cathedral ceilings/roof made up of 1.5 inch tongue and grove boards. A few years ago we added rigid foam on the roof and roofed over this. So rerouting the duct work isn't an option.

The terracotta pipe is large probably 8 inches and the wall thickness is 1 inch. I can see the pipe through the floor register (4x12). I can't see the misaligned area but can feel it by putting my hand about 1 foot into the pipe.

I too am concerned about why the pipe has moved after 50 years. I think the slab has moved about 1/4 inch this year. We have had the worst drought in 100 years, I wonder if the dryness has caused the settling.

I have thought about trying to insert an lining metal pipe into the existing duct work , but don't think I have enough room to insert through the register.

    Bookmark   November 28, 2010 at 5:06PM
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