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Thread: Tankless in a cabin?

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  1. #1
    DIY Junior Member Hermosa's Avatar
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    Default Tankless in a cabin?

    Hi,
    New here, been reading a lot, good info. I'm thinking of replacing the water heater in our cabin with a tankless unit. We are running propane, and we only use the cabin one weekend a month, so I don't want to be heating water 24/7 and using expensive propane if I don't need to. The climate is lake tahoe, so we have some cold weather, the water heater closet is accessable from a door on the outside of the cabin, vented from the outside also. The water heater is 20' from the shower, its a 1 bathroom place 700sf, really small.

    I would like to replace the current tank heater with a tankless in the same spot. I'm just worried it won't be able to heat the water nice hand hot given the incoming water is probably 30 degrees or cooler in the winter. I assume the shower load is 3.4gpm or less.

    This would save me a ton of money on propane. What do you guys think, am I looking at this correctly? any help appreciated! A tankless solution has really caught my attention for the cabin.
    Last edited by Hermosa; 09-19-2010 at 06:34 PM.

  2. #2
    In the Trades Gary Swart's Avatar
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    You need a tremendous amount of power, either gas or electricity to operate a tankless. In addition, they are extremely expensive to buy and maintain. I think the ton of money you think you will save on propane will be more than eaten up with the purchase, upkeep, and operation costs of a tankless. I'd consider turning the propane off and draining the tank at the end of the weekend of use.

  3. #3
    DIY Senior Member zl700's Avatar
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    LP tankless makes even more sense to you, but not so much to save on LP, if you turn the existing tank off due to non use when leaving. If you leave the tank on you use a bit on pilot (if one) and to fire to maintain temp.

    Problem with turning tank off is the water cools, condensation starts and the tank rots out prematurely. With a tankless, all stops and no more worries, in addition it is really easy to drain the 3/4 to 1 gallon from it stopping any condensation while idle and gone, along with any energy use caused by freeze protection kicking, not to mention eliminating any freeze concerns.
    If Payback is so important to you, why are you not driving a Toyota Corolla?

  4. #4
    In the trades Dana's Avatar
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    For a cabin off-grid going with something like the Bosch 1600H that doesn't require electricity for ignition, nor a standing pilot is about right. It pulls a respectable 0.80 in an EF test, and can be vented with cheap B-vent (unlike their only slightly more efficiency 0.82EF+ bretheren). It's enough burner to run a full-flow shower even in coldwater country, but would be a bit underpowered for a 2 bathroom + laundry situation (some cabin!) Since it requires no electricity and uses cheap vent pipe, it'll be a much cheaper to install than bigger-deal units.

    The standing-pilot versions of mid-efficiency tankless wouldn't be a disaster either. Just turn off the propane when you leave, re-light when you return.

    Just be sure the propane regulator & fuel plumbing can handle the full BTU rating of whatever you install- even the 1600H is 3-4x the burner of a typical tank heater, and more than many heating systems.

  5. #5
    Retired Defense Industry Engineer jadnashua's Avatar
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    Well, I doubt your incoming water is 30-degrees, but that's an aside! Low 30's, very common. In the fine print, the output temp or volume will start to go down as the inlet water temperature goes down. Most can do about 70-degree rise at the stated (big print) spec, and it drops almost in a line either in temperature or volume as the inlet temp drops. You might end up with a lukewarm shower on a really cold day, depending on the head, distance, and insulation. So, with near freezing water coming in, the volume you may have could be barely adequate for a shower, depending on the unit you select. There are some that would have no problems, but they tend to cost more.

    Do you maintain any heat in the cabin when you leave? Any water left in the tank OR tankless unit, if it is turned off with no other heat sources, is subject to freezing. If you drain the lines, and turn off the power, you have a chance. On the tankless units that are designed for freeze protection, depending on the space, they may not freeze internally, but there may not be enough heat to keep the pipes nearby from freezing, depends on the construction of the area and how cold and drafty it is.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  6. #6
    In the trades Dana's Avatar
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    To take a standard 2.5gpm shower with 32F incoming water and a fairly scalding 112F showering temp takes 100KBTU of output. A 117K burner with an 82-84% raw combustion efficiency (such as the Bosch 1600 series) can deliver that shower. (I lived with a similar sized E.L.M. with ~40F late-winter incoming water for over a decade- it kept up with a 3gpm flow, but not 3.5.)

    Most 2.5gpm shower heads deliver around 2gpm unless the water pressure is unusually high.

    Which is another thing to consider with any tankless: If your water pressure drops below 20psi it may lose efficiency due to insulating micro-bubbles on the water side of the heat exchanger. It'll even sizzle & bang a bit audibly if it goes as low as 10-12psi. Be sure the water system pressure is up to snuff before installing any propane-fired tankless.

    Freeze up of the heat exchanger can happen in very-cold climates even if the place is heated if the flue vent is short or side-vented. Draining the thing is probably a good idea if you're planning to leave it unattended during bitter cold weather.

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