Best tankless unit for a poolhouse

Discussion in 'Tankless Water Heater Forum' started by mikesm, Dec 21, 2018.

  1. mikesm

    mikesm New Member

    Joined:
    Apr 14, 2018
    Location:
    SF Bay Area
    Hi. As part of a new home build, we are also building a poolhouse that can serve as a guest house as well. It has a small kitchen inside, and a outdoor shower as well as a shower in a bathroom that is accessible from the inside as well as from the pool. Due to the space limitations, we are looking at an outdoor tankless gas unit to provide hot water to the unit. This is in the SF Bay Area, so mild climate.

    It's hard for me to tell which brand and model would be best suited for this. I can easily see both showers being active at a kids swim party, but not much draw from the indoor uses. It would get very little use during the week and outside the summer and warm days when kids are swimming. But when it does get used it would need to be able to support two showers pretty continuously. We aren't planning on putting a recirculating loop on the pool house right now, though we could if folks thought it was a good idea.

    Any tips for me or things to watch out for in selecting a unit? The plumber recommends a Takagi unit, but I have no idea on if it's a good choice or not. Does it make sense to get a unit like a Navien that has a small tank to avoid cold water sandwich etc....?

    Thanks very much!
    Mike
     
  2. Dana

    Dana In the trades

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    01609
    The cold water sandwich issue is only really annoying in cold water areas- wouldn't sweat that one too much in the Bay Area.

    Older Takagis were pretty rugged and low-maintenance. Scuttlebutt has it that they've slipped quite a bit after getting bought out, but I have no direct experience on that. (I've been heating my house & hot water with a Takagi KD20 for more than a decade now with exactly zero issues. YMMV) Takagi has pretty good tech support in CA and the call in tech line is willing to talk homeowners through diagnosing and fixing problems when they arise though, unlike most other tankless companies who restrict their help lines to professional plumbers/installers. If you trust the installer (have they installed dozens of Takagi?) it's probably not a terrible choice to go with their recommendation.

    Rinnai is the world's largest manufacturer of gas fired appliances, with solid product designs, a good reputation, and good product support in the US.

    Noritz & HTP sell some excellent tankless units manufactured by Kiturami, a first tier Korean vendor that competes head to head with Navien in their home market, but have a different strategy for the North American market. (Navien has built a distribution & support network here, whereas Kiturami OEMs their stuff to the American companies and leaves the support to them.) Westinghouse has a deal with HTP where they re-label them under the Westinghouse brand and provide their own support (moving a lot of them through Home Depot.)

    Any model 140,000 BTU/hr or bigger will work. Whether you can get away with an outdoor version (to save space) without freeze-up risk is really depends on your ZIP code's microclimate.
     
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  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Joined:
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    Retired Systems engineer for defense industry.
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    New England
    A tankless in this situation is probably a decent choice. I have no idea as to which brands or models would best suit your needs. Because things may have a short run, a tank may not buy you much.
     
  5. Dana

    Dana In the trades

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    Jan 14, 2009
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    The little mini-tanklet versions are to avoid the bit of cold water that gets by the heat exchanger during the ignition delay, not the length of the distribution runs. Ignition delays have gotten shorter over the past 25 years, and unless it's 40F or colder water coming in it's not really a big deal to most people.
     
  6. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Joined:
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    Occupation:
    Retired Systems engineer for defense industry.
    Location:
    New England
    A short run would mean that it won't take that long to purge the line of cold once the burner comes on. Even with a tank, you still have to purge the line, so it would be the line plus wait for the burner to come up to temp. At a typical flow velocity at max (you may not be at max velocity) of 5fps on a hot line, a long run verses the time it takes to turn on the burner is the major factor at the cost of additional complexity. If you want instant hot water, it can make a recirculation system work easier, where it might not be as easy with a tankless without one. The small tank also has a (small) impact on the overall standby losses. For example, say the heater was 50' from the point of use, that's 10-seconds at maximum flow rate, then add maybe 0.5seconds before the burner starts up and maybe another second to reach full temp. That's 11.5 seconds to get hot water.

    NOw, say you're only 5' from the unit, that's one second at max flow rate plus the same 1.5 seconds, or 2.5 seconds total, versus 11.5 seconds. Distance does matter.

    My flow rate numbers are decent, the unit's response time is more of a guess. Having a tank in the unit would shave off 1.5-seconds in my example.
     
  7. Dana

    Dana In the trades

    Joined:
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    Location:
    01609
    The cold water sandwich isn't about the first draw, but what happens on successive draws, when the distribution plumbing already has hot water in it. The ignition delay inserts a slug of colder water between that which had been heated in the recent draw, and the new draw of hot water. The mini-tank versions damp that out considerably.
     
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