HVAC ducting in insulated sealed crawl space?

HK45October 20, 2012

Designing a new 4000 sf house, two story on sealed insulated conditioned crawl space. Clear overhead is 4 feet.

Wish to use two HVAC units placed in adjacent attached garage, adjacent wall dividing house from garage. Location gives easy duct-way access to underfloor of floor 2 and crawl space under floor 1.

Crawl space foundation walls are ICF, R-22. Floor is heavy sealed membrane covered with 3" slab.

Unit 1 for 2000 sf main floor, unit 2 for 2000 sf second floor.

Ceiling heights are ten feet throughout house, but on main floor there are a number of false beams and lowered ceilings in small rooms and hallway drops that are designed into house to beautify it architecturally, plus provide space for ducting. Lots of space.

Main and only question: Is it appropriate to route all HVAC ducting for floor 1 in the crawl space?

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as long as 10 mil plastic vapor barrier
is continuous on ground of crawlspac.
mastic seal all duct connections, plenum
connections, returns and supply boxes
into house.

where are you building
and how are you conditioning the crawlspace?

best of luck.

    Bookmark   October 20, 2012 at 2:07PM
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Location of site is northern Illinois. HVAC contractor will engineer system to supply sufficient make-up air to crawlspace with return also, to maintain crawlspace at same temp as living space above, all year round.

    Bookmark   October 20, 2012 at 9:46PM
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Would subslab insulation be appropriate? Trying to maintain this space at 70 degrees will actually lose a decent amount of heat to the ground thru an uninsulated slab.

    Bookmark   October 21, 2012 at 6:22AM
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I'm sure it would be a great idea if not contraindicated. Lots of builders here are using a modular polystyrene block/form that insulates and, I think, incorporates the moisture barrier.

    Bookmark   October 23, 2012 at 3:19AM
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Just a note-polystyrene has been listed as a suspected carcinogen by the American Cancer Society since 2010 due to styrene leaching and off gassing. It is also a neurotoxin. I have smelled polystyrene and it produces an awful off gas. I would never consider it in my home.


    Bookmark   October 23, 2012 at 10:49AM
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You need a plastic vapour barrier OVER a concrete floor? I would have assumed there was a moisture barrier under the concrete, and that would suffice.

Where I am, Interior British Columbia, basement floors are bare concrete, and if finished, have carpet and regular underlay, or some sort of hardwood or laminate flooring with some sort of underlayment... but nothing that would really comprise a true vapour barrier.

A lot of the time, basement floor formwork is polystyrene, so it's insulated and moisture-proofed at the same time.

    Bookmark   October 29, 2012 at 9:09PM
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