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Community and Q&A

heat pump water heater in sealed crawlspace

carsonb | Posted in Mechanicals on

hello gba,
I am planning on putting a heat pump water heater in a sealed crawlspace.  If I follow the advise on here correctly for ventilating/dehumidifying sealed crawlspaces, this should then act as a free dehumidifier for the crawlspace and I would not need to put in exhaust fans/etc?   The crawlspace would have about 2000 cubic feet of air, so roughly 3x the minimum.  However, some of that may be above the unit so may affect air circulation.  I’m in zone5b, I don’t think crawlspaces here should reach freezing temps, but should I install some sort of backup heat to make sure temperatures stay above 50 when this is running?

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  1. Expert Member
    Dana Dorsett | | #1

    Are the crawlspace walls insulated to at least R15 continuous insulation? Are the floor joists insulated?

    If the crawlspace walls aren't insulated it's not going to be very efficient, most of the time.

    If the walls ARE insulated and there's no fluff between the joists isolating the crawlspace from fully conditioned space above, it won't need any auxiliary heating.

    If there's R30 between the joists it's at least conceivable that heavy hot water use could result in crawlspace temps that are too-low, but under light or moderate use that's unlikely.

    Since a water heater doesn't operate to a humidity setpoint it doesn't quite meet the letter of code as a dehumidifier, but in zone 5B it'll probably control the humidity to adequate levels just fine as long as there is some amount of daily hot water use.

    1. carsonb | | #6

      Thanks Dana, planning on rigid foam on foundation walls. Only a few spots will have floor insulation in joists where I’m putting spot radiant in. Despite Martins objections to radiant, putting electric radiant in for bathrooms and as a backup for bedrooms with ductless minisplits running most of the heating loads sounds like a great system to this novice.

  2. George_7224612 | | #2

    When I see the term "crawlspace", I think of a fairly shallow depth. HPWH are pretty tall. Will the one that you're looking at fit the space?

    1. Expert Member
      Dana Dorsett | | #3

      It's pretty easy to duct an HPWH into the crawl space, taking up less than 10 square feet of first floor.

      1. carsonb | | #5

        Putting hpwh into the house and ducting is an option, but we are limited on space. Digging out the crawlspace sounded better than getting rid of my small understairs pantry. That said, still an option.

        1. acrobaticnurse | | #7

          I'm curious what you ended up doing or if you're still in planning mode. I'm intrigued by the option of making part of a crawl space deeper to fit a HPWH.

    2. carsonb | | #4

      The reason crawlspaces are common here is excavation is so expensive, hence no basement. We will cut out a small area with a slab for utilities, however just for this. I guess that’s basically a mini basement.

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