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Best DHW for my situation

BobRVt | Posted in Mechanicals on

All,
We just purchased a small, single-level ranch with electric baseboard & wood stove for heat. The hot water is currently a propane 50 gallon tank in the laundry room, which is about 10’x5′. With the dryer going, the worst-case depressurization fails and potentially back-drafts the atmospheric draft hot water heater. The current water heater cannot stay, and there is no where else to locate it. The crawl has no inefficient source of household heat, and is only 4′ tall, less the joists.

The house is tight – about 1,300 CFM 50 for an 8,250 cu ft house. .44 ACHn. ( I know many of you don’t like that calculation. Let’s NOT have that discussion here, now!)

I have considered & eliminated the following:
Atmospheric Draft Propane Tank – see above
Sealed Combustion Propane On-Demand: too pricey to install & very slow payback, per several blog postings on this site.
Hybrid Electric Tank: Noisy & could chill the laundry room in the winter. The noise is my biggest concern. I was seriously thinking the wood heat would throw off enough excess to support this but the noise factor is important.

That leaves:
Electric standard tank – not very efficient
Electric On-Demand – expensive to install.

We do have 200A service & could disable a few of the electric baseboard circuits to suppor the On-Demand.

Thoughts & recommendations would be appreciated!

Bob

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Replies

  1. Expert Member
    Dana Dorsett | | #1

    The difference in efficiency between on-demand tankless and standard electric tanks isn't worth paying the upcharge on, if you're using at least 20 gallons/day.

    If you want to buy back some space in the laundry area, here are plenty of low-boy ~40-50 gallon electric tanks less than 36" tall that would fit in your crawlspace, provided you have an access hatch big enough to get it in there. eg: http://www.bradfordwhite.com/sites/default/files/product_literature/203-B.pdf

    The upcharge for a lowboy vs a standard height unit isn't usually very much.

    I'm not quite sure what means " The crawl has no inefficient source of household heat..." in your vernacular. Ideally the crawl space would be insulated & sealed, but even if it isn't that wouldn't necessarily be a deal-killer.

  2. BobRVt | | #2

    Regarding the lack of inefficient source of heat on the crawl, I mean there is no boiler or furnace that casts off waste heat.

    Yes, we'll insulate the rim joist and walls properly. Right now there is fiberglass in the crawl ceiling between the joists.

  3. charlie_sullivan | | #6

    Edit: oops, this was an old thread. Oh well, answer below anyway.

    Go with a heat pump:

    - Especially if you have a big enough tank, you can set up your heat pump to run at times that the noise doesn't annoy you, if that becomes a problem, which it probably won't.

    - Even if you were to disable the heat pump for the winter and use it as an ordinary electric tank, that's no worse than the regular electric tank , and you'd have the heat pump for the summer. (And as Dana pointed out, an electric tank is as efficient as tankless electric.)

    - You can get a duct kit and duct it take use hot air from near your wood stove. It will then run super efficiently and it won't cool the utility room.

    1. Wannabegreenbuilder | | #7

      All very good points.

  4. Wannabegreenbuilder | | #3

    What climate zone are you in? I would reconsider heat pump hot water heater as you can insulate for sound pretty easily. After a few days I quit even noticing mine as it was working because I got used to it.

    If you go electric on demand HWH have you considered solar assistance by prewarming H2O before it goes to the on demand? I’m just trying to think outside the box as I worry about your air quality. Your house is tight enough and small enough to have serious Air quality issues with combustion from your wood heat and possibly your cooking? I know it’s off topic but your air quality seems more important than sound from a Heat Pump HWH. I am making the presumption that you do not possess a whole house Ventilator because of your statement about the propane heater not venting when the dryer is on.

  5. this_page_left_blank | | #4

    I know this thread is ancient, but I can't resist commenting on how no one questioned the "house is tight" claim. Converting to standard units, it was almost 10ACH50. I doubt that even met code minimum of the time, let alone be within yelling distance of tight. My previous house was an 1879 wood framed brick facade with no air barrier, no insulation and stone foundation and it was in the ballpark of 10ACH50.

  6. 730d | | #5

    Is there a make up or combustion air vent in the area of the propane water heater ?
    That may be your solution.

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