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Community and Q&A

Electric Tankless – Guest Cottage

jnarchitects | Posted in Mechanicals on

We are working on a new project that includes a small guest house and a detached garage w/ office/ bedroom and bathroom above the garage. The main house is going to have a gas fired boiler w/ indirect loop for hot water.

But we are considering electric tankless for the guest house and garage bathroom. The thought is both of these spaces will be used very sparingly and why have an electric tank heating water for the weeks that someone isn’t there. The main house will be occupied about 50% of the time Mar.-Oct and less in the winter months. But during the “in-season”, people might be in the guest house for a week and then gone for 2-3 weeks (occupied even less than the 50% figure of the main house).

What seems like the most reasonable option for this scenario? I know the electric tankless units draw a lot of current particularly if a shower is running, but it seems like it might be a better option than trying to keep up with turning an electric tank up and down based on when the house is occupied.

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Chris,
    Your logic makes sense to me.

  2. jnarchitects | | #2

    Ok...Any particular recommendation on manufacturer? Steibel Eltron?

  3. Michael Chandler | | #3

    You need to consider the size and cost of the cable required to feed that much juice from your breaker panel. you may well discover that the cable to feed the water heater costs more that the water heater itself.

    Pick a heater that will serve the GPM of the shower and, assuming that the vanity will not be drawing hot water while the shower is in use and both are water sense rated fixtures you can then ask your electrician how much it would cost to feed power to both and compare that to the cost to feed a seven gallon "under counter" water heater located in under the vanity. the Ariston water heater is at Home depot for $219 and runs on a 120 volt 1,500 circuit that you would use for a microwave or hair dryer and can be fed from a wall switch to turn off when you aren't using the space. Water sense shower heads draw 1.5 to 2 gpm or less, assuming the temp is set at 120 and you are adding cold you will get enough for a 4-5 minute shower.

    If the bath isn't too far from the house you can supply the water to the water heater from the house water heater in 1/2" pex (home run) and then you can take as long a shower as you want have "instant hot when the switch is on and still have the ability to switch off the electricity on the way out the door.

    How do you plan to deal with freeze protection?

  4. mrbreadpuddin | | #4

    There are electric tankless heaters that exist only to look as if you are meeting the building code, but don't really make any hot water. A heater with a tank will produce more hot water and can be turned off pretty easily. Also all tankless heaters can fail if your water has a high mineral content.

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