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Should I expel my ventilation system air onto my hybrid heat-pump water heater? Should I vent the WH into my crawl space?

user-1140356 | Posted in Mechanicals on

For a superinsulated house being extensively retrofitted in South Jersey (R-40 walls, R-70 attic, triple pane windows) with a permanently wet crawlspace (riverfront, high water table), I am considering positioning the exhaust duct from the Fantech heat recovery ventilation system to expel over the top of a hybrid heat pump hot water heater. The HWH will be in the insulated unheated 2 car garage, possibly next to a geothermal water-to-air heat pump. I would plan on turning that exhaust vent away from the HWH in summer. The GE HWH unit I’m considering has an add-on kit for directed venting so I could attach the Fantech HRV exhaust directly. The heat pump is under consideration since the geothermal system may actually be less costly than 3 mini-splits.

If I add a geothermal heat system should I enclose the geothermal system with the Hot Water Heater in a 6 x20 utility room built inside the garage or leave it out in the insulated garage?

Should I vent the exhaust and/or intake from the HWH into my crawlspace in summer? The crawlspace has significant water infiltration and significant humidity. I would plan on turning that vent back into the insulated garage in winter.

Any thoughts on getting the most efficient setup are appreciated.

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  1. GBA Editor
    Martin Holladay | | #1

    Lots of questions.

    First of all, if you build a utility room for your heat-pump water heater, the room has to meet the minimum volume requirements established by the water heater manufacturer. Too small is no good. Your 960 cubic foot room might just barely be big enough. More information here: Heat-Pump Water Heaters Come of Age.

    If your heat-pump water heater has fittings for ductwork, it likely has both an intake and an exhaust port. If you hook up your ventilation system exhaust to the intake of your heat-pump water heater, make sure that the air flows match. If you aren't supply adequate air flow to the water heater, it won't operate efficiently.

    I'm a little suspicious of any ducting arrangements that require readjustment every spring and fall. Experience shows that homeowners either get tired of the twice-a-year chore, or sell their house to an ignorant new owner who never operates the equipment properly.

  2. user-1140356 | | #2

    Thanks for your response, Martin.

    Given your caveats (I will be careful to match the flow rates, I plan to keep the house myself -- at least to the life of the heat pump or my own and, though somewhat ignorant, I am anal retentive enough to switch the vent twice a year), I still would like your opinion: is this worth doing?

  3. GBA Editor
    Martin Holladay | | #3

    It isn't necessarily a good idea to run your ventilation system for 24 hours a day. You can save energy, for instance, by turning the ventilation system off when everybody has left the house.

    Your heat pump water heater won't be running for 24 hours a day, of course; it will turn itself on and off as needed. So your suggested arrangement has to come up with a way to address the mismatch -- the non-simultaneity -- between the flow of ventilation air and the flow of air needed by the heat-pump compressor.

  4. user-1140356 | | #4

    Excellent point. Thanks very much. I suppose I will simply direct the HRV exhaust at the water heater in winter.

    How about pushing the cold dry air into my humid crawlspace in summer? Worth it? Or is there a problem I'm not recognizing.

    Thanks again, Martin. If you are ever in South Jersey, you are very welcome to come by and visit. I really appreciate the website you have created here.

  5. mackstann | | #5

    There is a ducting add-on for the Geospring? I can't find anything about such a thing.

  6. GBA Editor
    Martin Holladay | | #6

    I think you are thinking of the AirGenerate Air Tap unit, not the Geospring unit.

    Information from an online web forum:
    "The only heat pump water heater manufacturer that allows for ducting that can pull air from the exterior of the home & exhaust cold air to the outside is AirGenerate out of Houston, TX. Using air from the outside and exhausting cold air to the outside of the home maximizes savings with heat pump water heaters. Here comes more information:"

    Here is the link again: Direct-vented Air Tap water heaters.

  7. mackstann | | #7

    Martin, I was just going off of where Michael said, "The GE HWH unit I'm considering has an add-on kit for directed venting". Maybe GE was a typo.

  8. rpertusio | | #8

    FYI, the GE GeoSpring ducting part # is: GVK8HS

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