tankless waterheater

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by strainsa, Nov 22, 2004.

  1. strainsa

    strainsa New Member

    Sep 2, 2004
    I am looking into replacing an electric water heater that supplies two bathrooms and was wondering if anyone had any thoughts or experiences or opinions on electric tankless water heaters.
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Sep 2, 2004
    Retired Systems engineer for defense industry.
    New England
    If both bathrooms are going to be used at the same time, or if you have a tub that is used regularly, think twice. Most of them have a limited flow and it will take a long time to fill up the tub. They have a flow restrictor on/in them to ensure the water has enough time in the heater to get the temperature rise. Last, most are designed to raise the incoming water about 70 degrees max. Where I live, my incoming water to the house last year near the end of the winter (it was a cold one here in NH) was in the low 30's. That was the straw that caused me to decide to change mine out. I'm planning on doing it in the next month or so to an indirect heater, warmed by the new boiler I'm also having put in. They are very common in other parts of the world, but energy and water are usually much dearer. They don't take long hot showers or have big whirlpool baths in general, either. They work pretty well in those circumstances.

    You'd need to have a significant electrical service, too. While they don't run when not needed, in order to heat the water, they need a bunch of amps while they are doing it. A natural gas one (or propane) could do it, too. You need to supply combustion air and vent them well. A direct outside vent for supply air is best.

    For the right circumstances, they are great. I'm not so sure that for how we like to do things, they are the best idea. Look around, check their specs (look for max gallons per minute and temperature rise) and decide. A shower head takes on average about 2.5 gallons per minute. A tub filler more like 6-12, depending on the supply pipe an dthe valve design. If you use hot water occassionally for your washing machine, 40 gallons or more at 3.5 gallons per minute, about 12-13 minutes to fill. A tub at say 35 gallons, 10 minutes.
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  4. hj

    hj Moderator & Master Plumber Staff Member

    Aug 31, 2004
    Cave Creek, Arizona

    A tankless that would run two showers at the same time would have to be in excess of 120 amps, which would tax most residential 200 amp service wires.
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