Sealed crawlspace next to walkout basement with HPWH
Greenville, SC
CZ 3A (mixed humid)
Extensive rock has limited the amount of basement I can put in, so I will have a rather tall crawlspace adjoining my walkout basement on two sides. The basement will have interior foam insulation (R-10) on the poured concrete walls, R-20 on the walkout side, and will be unfinished for now. The crawlspace will be sealed and also insulated to R-10.
The crawlspace will also be tall enough at a point below my master bath and a guest bath to install a heat pump water heater. This will serve as a dehumidifier, as well. Overflow, pressure relief and condensation will drain through sealed openings in a CMU wall to the exterior. I plan to put the water heater in a pan on top of a lightweight concrete pad similar to those used under outside HVAC units (I am thinking the pad will rest on the ground (level of course), then the liner, followed by the pan). There will also be a drain at the lowest point in the crawlspace liner to allow any water from leaks to get out. Appropriate varmit barriers and insect screening will be applied to the drain.
Per code, I need to provide a forced air vent into the crawlspace, though I doubt it will be needed all that much with the water heater doing its thing. This should be easy to do since my ducted mini-split air handlers will be in the crawlspace Most write-ups I have seen dictate a return path to the conditioned space from the crawlspace. Can this be into the unfinished basement? Will the basement need to be conditioned to do that? (was planning to add that later to save some cash now).
Does this plan sound doable and appropriate? Any suggestions/things to avoid/things I am missing?
Thanks,
Norman
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Replies
Norman,
Q. "Most write-ups I have seen dictate a return path to the conditioned space from the crawlspace. Can this be into the unfinished basement? Will the basement need to be conditioned to do that?"
A. The only person who can answer that question is your local code authority. The opinion of anyone on this website is irrelevant, because your local code authority makes the determination and interprets the code.
That said, I think your crawl space will be dry. You're instincts are correct: the heat-pump water heater will act as a dehumidifier. I hope that your code official is flexible on this issue.
Of course, once you have your certificate of occupancy, you can operate your house any way you want. If you determine that a forced-air supply register in the crawl space is unnecessary, you can seal it up.