Where to locate HVAC ducts in vented crawlspace
I’m in climate 4c (Pacific northwest) and looking to put HVAC ducts in a vented crawlspace of a future build. Vented crawlspaces do well here in the PNW and I prefer to not condition it. Attic is also vented.
My contractor gave me two options:
1. Run insulated HVAC ducts in an open web floor truss system
2. Run insulated HVAC ducts in a chase running under the floor system
Will these options be a recipe for moisture issues? I’m worried that if/when HVAC ducts leak, I’ll have a wintertime situation where warm air will hit the cold floor truss framing, condense, and lead to moisture issues.
There is also option #3 – condition the crawlspace, and run ducts in the open web floor trusses, but that comes with its own challenges (radon mitigation, dehumidification, etc).
Janelle
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Replies
My choice ranking would be 3, 1, 2.
I think 3 is the only real option in that option 1 &2 have the unrealistic presumption that someone could and would seal every possible air leak between the conditioned space and the vented crawlspace.
Put a passive radon system under a rat slab now and only install the fan if you have a problem. If you truly condition the space by installing supply and return registers the humidity in the crawlspace will be the same as the living space.
If you do condition the crawl space consider making an outdoor entrance and a utility room with 7 foot of head room for the water heater and HVAC assuming you can have a floor drain that will find daylight on your property.
Walta
Janelle,
When we say vented crawlspaces work in the PNW, we really just mean they don't experience the moisture problems they do elsewhere, not that they function well, or are the best option.
Like DC and Walta I'd pick option #3.