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Hot Water Heater for an Energy-Efficient Home

qofmiwok | Posted in Energy Efficiency and Durability on

What is the best kind of hot water heater for a highly efficient home?  Only 2 people, CZ 6.  I was thinking about a combi boiler to do radiant, but we’ve scaled radiant back to just 5000 BTU in the garage, so that’s probably not worth it if I have to pay $5k+ for a combi boiler.  I see DHW solutions from $800 to $7000 and I don’t understand the difference.  The usage for an reasonable efficiency gas water heater is about $150 per year, so efficiency isn’t that critical.  We have NG available and it is super cheap.

I should probably add… My conditioned crawlspace is where my mech room is supposed to be, but it is only 4.5′ deep due to potential seasonal groundwater issues.  So for a taller one (which all are except on-demand and combi-boiler) I would have to put it in the adjacent garage.   I also want a recirc pump.

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  1. Steve Knapp CZ 3A Georgia | | #1


    I'll throw out a couple of comments to give you a bump. I'm not sure if radiant makes much sense just for the garage (but maybe it does). I know there have been several threads on this topic, but I don't recall a consensus on what might make the best solution.

    FWIW. I would consider insulating the garage slab and structure and then look at using an electric or NG fired heater that could be set to keep the temperature above freezing. Personally, I much prefer the all-electric approach, but I live in an area where kwh are pretty cheap.

    If you did decide to go electric for DHW, you could put a "short" 50 gallon Marathon in your crawl space.

  2. qofmiwok | | #2

    Thanks for the reply. Yes we are insulating the garage slab. On the Marathon, I'm not sure how much space they need for connections in addition to the 47.25", so not sure it will fit. But also the plastic gives me a big of pause. Of course we're using Pex which is "plastic" too so maybe I shouldn't be worried about the tank.

  3. Expert Member
    Akos | | #3

    Some water heaters can be ordered with side ports. This way you only need enough room on top to run the electrical feed into it. As a bit of extra insurance for flooding, you can also install the heater on a GFCI breaker.

    A smaller volume water heater can usually be made to work if you order one with larger elements, install a mixing valve to be able to run the tank much hotter and use DWHR.

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