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HPWH – To duct or not to duct?, that is the question

NormanWB | Posted in Energy Efficiency and Durability on

As noted in an earlier question, I will be putting a heat pump water heater in my crawlspace. The Rheem unit I have allows ducts. I want to get the maximum circulation of air in my crawlspace to dehumidify it and am wondering if ducting the cooled exhaust to the far end of the crawlspace might be worth it. Rheem says I can use up to 125′ of 8″ flex duct, which should be more than enough.

Does ducting result in any penalty as far as efficiency? I am thinking it will be a wash, since moving the cooler air to a higher point in the crawlspace should result in more circulation as it travels back toward the unit, picking up heat and moisture on the way.

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  1. Expert Member
    Dana Dorsett | | #1

    Have you verified that the crawlspace has the requisite minimum volume required for the HPWH?

    The more duct impedence, the lower the air flow, which will impact the as-used efficiency. If flex duct, stretch it out as straight & tight as possible. Using hard piped duct with as few ells as possible is usually lower drag/higher flow. The duct does not need to be insulated.

  2. NormanWB | | #2

    Yes, I have checked the minimum volume requirements and am well in excess.

    I plan on a straight shot to a corner, where I will gently point the duct into that area. No ells are planned.

  3. Jon_R | | #3

    My guess is that the horizontal exhaust was designed with enough throw that ducts would be a net loss.

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