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Thread: Hot Water for a very small house

  1. #1

    Default Hot Water for a very small house

    I'm remodeling a small summer house this summer. It is acutally a glorified shed behind the actual summer house. There is a sink and toilet that is fed by a cold water pipe from the main house. I'm looking to put in a shower and something to make hot water. Does anyone have any suggestions on a small, inexpensive electric water heater. It will be providing water for 2 or 3 showers a day, for a couple weeks a year in the summer. The house will be drained by Labor day. Has to be electric, there is no gas or oil in the house.

  2. #2
    In the Trades Gary Swart's Avatar
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    Unfortunately, there is no small, inexpensive solution to this. A small point of use heater is cheap enough, but not large enough for showers. I would look at a 40 gallon GE/Rheem heater. Probably more capacity than you need, but anything smaller would be about as costly. You will need 220VAC service.

  3. #3
    In the Trades Bob NH's Avatar
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    You can operate a 240 Volt heater on 120 Volts.

    Most 240 Volt heaters have two 4500 Watt elements and have control switches to give priority to the top element. If you connect it to 120 Volts the power will be 1125 Watts (9.4 Amps) so you can operate it on a 15 Amp circuit.

    It will deliver 3840 BTUs per hour, which will give you about 7.6 gallons per hour at 60 F temperature rise. That should be ok for summer use.

    If you set the temperature fairly high, use a low-flow shower head, and space the showers out over the day, you will be ok with a 40 gallon heater.

    If you have reasonable DIY skill you should be able to install it yourself, or with a bit of help from an experienced friend.

    It is probably not to code (I would have to check) but you could put a cord on it and plug it into a convenient outlet. Then use some CPVC to hook it into the plumbing.
    Last edited by Bob NH; 04-17-2008 at 02:17 PM.

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    Master Plumber Redwood's Avatar
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    That 120 volt installation would then take the 40 gal. water heater and turn it into a glorified Mr. Coffee with a very slow recovery rate and the same energy cost to operate. 1/2 as much twice as long!

    I would run 240 volt if it is not already there!

  5. #5
    36 Journeyman Plbr rudytheplbr's Avatar
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    Default Hot water

    You could use a 110 volt on-demand w.h. and a really small shwr head.
    RUDYTHEPLBR

    EAT "WILD ALASKA SALMON" IT'S GOOD FOR YOU AND YOURS.

  6. #6

    Default Wow, Thanks

    Thanks for all the info. What is the difference between tankless - on demand - and point of use water heaters? Is any one type going to be better for my small house project.

  7. #7
    Moderator & Master Plumber hj's Avatar
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    Default heater

    On demand heaters have a high input high capacity. Point of use heaters use flow limiters to reduce the flow to the degree that the heater can raise the water temperature. The resultant flow is so miniscule that it is only, barely, adequate to wash your hands. Water heater elements have a constant amperage so as the voltage goes down so does the wattage, but the wiring and circuit breaker still have to support about 20 amps. It would be better to replace the 240v elements with120v ones. But a 120 v. electric water heater would have such a pathetic recovery rate that the tank should be larger to have some chance at providing enough capacity.

  8. #8
    In the Trades Bob NH's Avatar
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    Quote Originally Posted by hj View Post
    But a 120 v. electric water heater would have such a pathetic recovery rate that the tank should be larger to have some chance at providing enough capacity.
    ". . . when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind; . . ." Sir William Thomson (Lord Kelvin)

    So let's put a some numbers to it.

    bigdcarter said he needed to support 2 or 3 showers per day in the summer.

    Putting in a 240 Volt circuit is a good idea if bigdcarter wants to run a 30 Amp circuit to the "glorified shed", with enough additional power to run the rest of the house. But if he doesn't want to run that circuit then it can probably meet his needs with a 120 Volt circuit.

    Putting 120 Volts on a 240 Volt heater gives about 7.6 gallons per hour at 60 degrees temperature rise. That is a reasonable temperature rise for the summer. If he sets the thermostat at 150 F it will store the same energy above 60 degrees in the water as a 60 gallon heater at 120 F.

    That is enough to provide three 5-minute showers at 2.5 GPM, and more if one uses low-flow shower heads.

    It can provide even more hot water over the day, since 7.5 gallons per hour x 24 hours is 180 gallons. That is more than most people use.

    A point of use heater is a small tank unit (2.4 to 4 gallons) that is suitable for a sink but not very good for a shower.

    An instant heater would be completely unsatisfactory. You might get 1 QUART per minute on a 120 Volt circuit.

  9. #9
    Retired Defense Industry Engineer jadnashua's Avatar
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    If you run the WH higher than 120, and it is a good idea to keep it from growing things inside, it is highly recommended to install a tempering valve to knock the temp down on the output for safety.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  10. #10
    DIY scratch-pad engineer leejosepho's Avatar
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    Have you thought about solar? My wife and I used to live on a houseboat, and we got our hot water from a black 30-gallon tank sitting in a glass box on the roof. For just a couple of weeks per year, something like that might be your simplest way to go ...

  11. #11

    Default

    leejosepho,

    Solar might be an option, but I'm not sure how well it would work in VT, plus I'm installing this shower with my brother and father who are very anti-change.

  12. #12
    In the Trades Bob NH's Avatar
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    You are unlikely to recover the installation cost of solar in something that you will use for two months of the year.

    Hook it up with 120. If you find that is unsatisfactory you can run a 240 Volt circuit later.

  13. #13

    Default In Addition

    Thanks guys. In addition I'm planning on plumbing the glorified shed with PEX. Should I use 1/2 inch or 3/4 inch. The water pressure coming to the house is below average. IN addition, does anyone know of a web site or store to buy a reasonably priced pair of Pex crimpers. HOme Depot had them, but for just under $100.

  14. #14
    In the Trades Bob NH's Avatar
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    Consider CPVC. Costs less. No special tools. Mice won't eat it in the winter.

  15. #15
    Master Plumber Redwood's Avatar
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    Raven Products makes a crimper for stainless steel clamps that sells at many supply houses for about $50.http://www.ravenproducts.us/pex.htm#clamps



    I would not recommend installing CPVC in an unheated crawl space in Vermont... No way! No how! CPVC gets very ugly when it freezes while pex is very forgiving.

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