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Community and Q&A

Installing Heat Pump Water Heater Outside

GFred | Posted in Energy Efficiency and Durability on

I would like to get a Heat Pump Water heater for my new ADU. However, they all seem too tall to place in the small attic we have. Most units are 60” tall or more. So, I am wondering about placing it outside. I know there a split systems where just the compressor is outside, but I’m considering the feasibility of placing the whole unit outside. Are there units that can take the rain & the potential rust issues, or would these need to be in a doghouse? As an Architect, I can imagine a huge future need to replace lots of exterior tankless gas units in the future too. It would be hard for many people to give up valuable interior space to just upgrade their water heater.

So really 2 questions:
1. Are there a low profile versions for attics?
2. Are there better brands, or best practices for placing one outside?

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  1. Expert Member
    DCcontrarian | | #1

    They're not meant to go outdoors.

    You can get an add-on heat pump that works with any electric tank. Here's an example, I don't have direct experience with it:

    I have something similar in my summer home that I installed years ago before heat pumps were widely available. It has served reliably for over a decade. But that model is no longer sold.

    1. user-5946022 | | #5

      The website you linked has no "add on heat pumps." They only have tankless water heaters, which are certainly NOT heat pumps...
      Can you clarify what you are trying to refreence?

      1. Expert Member
        DCcontrarian | | #6

        Somehow the link got clipped. Here's the link I intended:

        1. Expert Member
          DCcontrarian | | #7

          See also this link:

          What I have is by Nyle as well, I think it's an early version of the Geyser product. Interestingly the Hubbell product also goes by Geyser.

    2. tim_william | | #11

      That's really clever. Unfortunately it costs more than an entire heat pump water heater (we get a substantial rebate here in Maine). Is the value in not throwing away a working electric water heater?

  2. freyr_design | | #2

    There was recent discussion of phase change water heater that is compatible with heat pump:

    Edit: I hadn't actually clicked on that product in the discussion but it seems unclear if they are compatible with heat pump... the homepage says they are but the products don't mention it.

  3. wastl | | #3

    Such a unit can be put outside if it does not freeze or experiences condensation (and no rain etc.).
    Is that given at your site?

    1. GFred | | #8

      I’m in Southern California where we don’t freeze. So, I’m thinking maybe a little shed roof is adequate to just keep rain off it. At the most a small doghouse should be enough.

  4. amorley | | #4

    How much vertical space do you have to work with in the attic?

    1. GFred | | #9

      I have about 60 “ clear at the very top of a shed roof attic. Rheem 50 gal models are about 5’ but they need 6” clearance on top to change the filters, and make connections.

      Have you seen one that’s shorter for 50 gallon capacity, or more?

      1. Expert Member
        MALCOLM TAYLOR | | #10


        If this is a new build, would it not make sense to find space in the floor plan for it (or whatever may replace it in the future)? Putting it outside smacks of the kind of second best solution usually associated with a retrofit situation.

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