*
We are looking at a basement re-model and extension, and want to avoid the big ugly soffet on the ceiling for the heating ducts.
Since we are excavating and pouring a new slab, one idea was to bury the heating ducts and air return in the slab. Apparently this is common in large commercial jobs, but I haven’t heard of it being used in residential.
Does anyone have any knowledge or experinence of this?
Replies
*
Dates back to Roman times. The had a fire in a half basement and the flue gasses went through passges under the stone flooring. Early radiant floor heat. Of course they had slaves to keep the fires burning.
Sorry, don't know the specs for that below-slab ductwork. Interesting design question though - do you want that ductwork to be insulated so as to not lose any heat along the way? Or do you use uninsulated ductwork/piping to add a radiant floor heating component to the scheme?
*Actually, it is done fairly frequently. I recommend using PCD coated spiral duct, which is designed for installation under slabs. If you talk to your local HVAC supply, they will undoubtedly be able to help you.
*As noted it's fairly common in slab construction.Personally, I wouldn't do it. The chance of mold growth in the ducts is enough to cool me on the idea, plus it limits the options if you have to have termite treatments.Reasonable people may disagree on this subject.
*I did an underslab duct system. I used 8"and 6"PVC pipe.Boxed out for registers and it is working well today, its 5 or6 years old. The concret sealed the exitside of the supply. However there are several underground duct systems check with hvac contractors.Charlie in tn
*Joes Building Science site says that it is a major mold danger.near the stream,ajhttp://www.buildingscience.com
*I can't really comment on whether or not it is a mold hazard. The PCD spiral ductwork comes standard with a 4 mil polyvinyl coating on the outside, but can be ordered wth a 4 mil coating onthe inside as well. I would think that would be a fairly mold-resistant environment. I do know that it is specifically designed for under-slab use, and they have all the fittings and pieces to make it work.http://www.foremostduct.com
By the way there is a new underground duct product called AK Duct, UL listed for 0 air-loss up to 4" water column and approved (FEMA inspectors have checked code approvals and recognized as approved) for 3' under flood plain as well, also its UL 181.11 listed as Antimicrobial, ie, you can flood and then flush out and reuse, using it on the Eastern Shore of Maryland for Flood plain construction, in slab construction, this way saving the builder 18-30" of crawl space construction costs not available with other underground products. also Unless approved all others must also incase in 2" of concrete another major hasssel and cost factor that has driven us to build soffits or put overhead.