Help with a tankless idea

Discussion in 'Tankless Water Heater Forum' started by Mr Bo Jangles, Mar 30, 2019.

  1. Mr Bo Jangles

    Mr Bo Jangles New Member

    Mar 30, 2019
    I'm considering an electric tankless water heater as a large portion of electric costs is from the 40 gallon tank heater I have now. A small tankless is around 500 bucks so fairly affordable.
    I live in a mobile home in Maine and most of the time it's just me and only run one appliance at time.
    I was thinking that I could unplug the current water heater so it could be used as a holding tank keeping the water at room temps. The outdoor temps get well below zero in the winter and the water coming in I would guess is slightly above 40 degrees F.
    Would there be any issues putting a tankless directly after the current regular water heater?
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Sep 2, 2004
    Retired Systems engineer for defense industry.
    New England
    You probably do not have enough power to do much of anything with an electric tankless. A tank has the luxury of taking a long time to warm the water up. The tankless must do it as the water passes by the heat exchanger. WIthout a huge electric load, you won't get much flow, or you'll end up with tepid water. IMHO, most electric tankless are a joke, and maybe good for hand washing, but little else. Say your water stored in the tank averaged 70-degrees and you tried to raise it to 11o using a 2.5gpm showerhead. That would take 122 amps or so to do it. Lots of utilities charge for maximum demand, so your service base rate would likely go up and people on your transformer would likely complain when your tankless turned on.

    Throw some more insulation around your tank. Electric WH are pretty efficient. Keep in mind that any heat it leaks off in the winter is just that much less energy you need to heat the house...IOW, it's not losing much.
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  4. Dana

    Dana In the trades

    Jan 14, 2009
    Not one utility in Maine has a residential demand charge in their rate structure. (Hasn't happened there yet.) Only a very few utilities in the US have residential demand charges, a few in Alaska, and I believe one or two targeted only at homes with rooftop solar in Arizona. The residential demand charge for solar ratepayers Eversource managed to get approved in part of Massachusetts was very short lived, taken out by legislative action. Could happen someday, maybe, but hasn't.

    That's not to say that residential demand charges aren't eventually going to be the standard, but it will be years or even decades, with lots of political push-back before that can happen. It's arguable that people with extremely heavy intermittent loads like tankless water heaters or 10 ton air conditioners SHOULD be paying more for the wear and tear those loads put on the local distribution grid though.

    That said, there isn't much savings to be had going from 92% efficiency to 99% efficiency. Using the tank water heater as a tempering tank isn't very effective either unless the insulation gets stripped out of it, and that would create a condensation drip moisture problem in summer. Unless you're heating the house with some incredibly cheap fuel there's no way a tempering tank is going to be "worth it". Spending the money on a small rooftop PV system instead of a tankless would have a better return on investment.

    Before that, a very low-flow shower head would be a cheap investment with a high rate of return, if you're a showering person rather than a tub-bather.
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