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Community and Q&A

Optimal water heater ventilation

Cody Hazelwood | Posted in Energy Efficiency and Durability on

I’m self-contracting a Zero Energy Ready Home build in the southeast US.  It will be pretty tight (less than 2.5 ACH 50).  We will have a conditioned crawlspace and an unconditioned attic.

I’m trying to determine the best place to locate my hybrid hot water heater.  The model I’ve chosen has a duct kit and has several supported configurations for only exhaust, only intake, no ducts, or both ducts.  Originally I was considering placing the unit in the crawl space, however it is just too big and we would incur a lot of cost and difficulty to make part of the crawl space 6-7 ft tall to support it.  Instead, I’m considering placing the hot water heater in a closet, or in the utility room (small), but I’m not sure what the best place to vent it would be.

Here are options I’ve considered:

– Air intake and exhaust to the attic
    Pros: plenty of heat for most of the year
    Cons: another hole in the envelope, attic dust

– Air intake and exhaust to the exterior
    Pros: sufficient heat for most of the year
    Cons: another hole in the envelope

– Air intake in the laundry room and exhaust in the crawl space
    Pros: no hole in the envelope, adds some ‘conditioned’ air to the crawlspace
    Cons: using HVAC energy, cooling floors in the winter

– Air intake and exhaust in the crawl space
    Pros: no hole in the envelope, dehumidifying effect
    Cons: using HVAC energy, cooling floors in the winter

Any suggestions as to the best approach, or alternatives I should consider?

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  1. GBA Editor
    Brian Pontolilo | | #1

    Hi Cody,

    What specific water heater are you planning to use?

  2. Expert Member
    Akos | | #2

    Being in the south, I think the best use would be to connect it to the crawlspace and get that extra bit of dehumidification and cooling.

    If you are worried about cold floors, could add a set of damper so you can direct both intake and exhaust to the outside in the winter. I doubt this is worth the cost or complexity.

    I don't think it will do all that much to cool the floors, the water heater is not running all the time, the temperature there will be more of a function of ground temperature and amount of heat from the furnace.

    1. Expert Member
      Dana Dorsett | | #4

      +1 on that approach, of the options listed. But there is yet another option:

      In an air conditioned house drawing from unvented crawlspace and exhausting into the conditioned space room with decent sized a return register for the HVAC would be another reasonable approach, with a floor grill on the far end of the house from the water heater to allow conditioned air into the unvented air into the crawl. For unvented crawlspaces code requires an average ventilation rate of at least 1 cfm of conditioned air for every 50' of floor area, so the water heater would be providing that service (and then some.) Most heat pump water heaters are running well over 100cfm, and run long duty cycles, so the average would likely be multiples of the code-minimum unless it's an unusually large floor area.

      That approach neither heats nor cools the floor, and won't overcool a room large enough to need a large return vent. During the heating season the cooled air is drawn into the heating return, slightly raising the heat transfer efficiency on the furnace or heat pump. If the laundry room has good air communication with the rest of the house that might be a good location for exhausting the cooler drier air, since most of the time it won't matter if it overcools the room slightly (unless the laundry room is where you tend to hang out with friends & family. :-) )

  3. Cody Hazelwood | | #3


    We're looking at the Rheem Performance Platinum 50 or 65 gallon:

    Thanks - that's what I've been leaning towards, since the original plan was to put the water heater in the crawlspace anyway.

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