Electric Tankless Water Heaters?

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by gswanjr1, Jan 4, 2008.

  1. gswanjr1

    gswanjr1 New Member

    Messages:
    4
    I have been considering an Electric Tankless Water Heater.... ANY questions, comments, or concerns I need to consider??? Thanks in advance!!
    Last edited: Jan 4, 2008
  2. Squ1rrel

    Squ1rrel New Member

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    69
    Location:
    Texas
    What kind of demand are you looking at? Alot of electric tankless units have difficulty supplying a decent amount of water.
  3. gswanjr1

    gswanjr1 New Member

    Messages:
    4
    I have 2 sinks, a dishwasher, a toilet, a shower, and washer downstairs; and two sinks, a tub, and a toilet upstairs. But maybe 2-3 of these would be used at one time. Thanks.
  4. portiz

    portiz New Member

    Messages:
    5
    I may have to agree with Squ1rrel. If you really want to use electric tankless water heaters then install two or more of these in parallel for simultaneous demands of hot water.
  5. srdenny

    srdenny Plumbing Contractor

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    Location:
    SF Peninsula
  6. Squ1rrel

    Squ1rrel New Member

    Messages:
    69
    Location:
    Texas
    Even those can only run about 4 GPM at a 50 degree rise on their strongest unit. That translates to about 2 showers at once with 70 degree water coming in...colder water than that and the gpms drop. and that unit takes ALOT of power, 300A minimum service. Also, ask your electric company. I know in some places, they actually recommend that you do not use a electric tankless for whole house use.
  7. GrumpyPlumber

    GrumpyPlumber Licensed Grump

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    Location:
    Licensed Grump
    Gas tanklee - yes.
    Electric tankless, from what research I've done, not worth the added costs to upgrade.
    The only savings on electric tankless is in standby heat loss, which is minimal compared to the installation cost.
  8. Bob NH

    Bob NH In the Trades

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    3,317
    Location:
    New Hampshire
    (4 GPM x 8.34 #/gal x 60 min/hr x 70 degree temp rise)/3413 BTU/kWHr = 41.05 kW = 41,050 Watts.

    41050 Watts/240 Volts = 171 Amps. That will require a 200 Amp circuit, which is as big as the entire electrical service connection for most houses.

    Many power companies take a very dim view of putting those kind of intermittent loads on their transformers because it makes the lights dim for all of your neighbors.

    My experience with electric instant heaters in Europe is that they don't give stable temperatures because of the ON/OFF switching that is often used to control them.

    4 GPM is ok if you aren't using the washer or dishwasher while you are using the shower, and if you are not filling a tub while taking a shower in another bathroom.

    70 degree temperature rise is OK if you are getting water that is not below 60 degrees in the winter. If you are getting municipal water from a surface source north of the Mason-Dixon line then you need to plan on 35 degree water supply and at least a 90 degree temperature rise (28% more Amps).

    If you want instant water heating and don't have natural gas, it would probably be better to get a propane-fueled instant water heater.
  9. GrumpyPlumber

    GrumpyPlumber Licensed Grump

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    Exactly what I suggest when I get a customer who requests info on an an electric.
  10. hj

    hj Moderator & Master Plumber Staff Member

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    26,176
    Location:
    Cave Creek, Arizona
    tankless

    At least you did not ask for a "good" electric tankless water heater, because that might be impossible to find.
  11. Hey GP on that customer of mine with the 50 gal PV,


    he's opted to fish a electrical feed for me to install a 82 gallon electric to add into the mix of demand to the powervent.

    That's almost 100 gallons of ready to use hot water, no ceilings have to be opened up, no large expense for tankless or piping to install a larger powervent *75*


    82gal elec wh is $439 + tax, install will be at least $450, electrician figure $400 easily.

    Roughly $1300, no drywall work, two heaters running when needed with a very slight chance of blowing through that much water.

    I'm thinking I'll have to pipe those water lines symmetrical off the tops of those tanks, one of them being almost 2' shorter than the other.

    That way the water draws evenly from the hot side.


    Everything else puts the situation in the 3-6 thousand range quite easily, drywall work on a specific/unusual stippled drywall ceiling.

    Your thoughts..................?
  12. Bob NH

    Bob NH In the Trades

    Messages:
    3,317
    Location:
    New Hampshire
    It would be better to put the 80 gallon electric in series with the 50 gallon PV, with the electric as the second stage. Then the gas will do the heating and the electric will be a maintained temperature storage.

    When there is high demand the gas heater will be working to refill the electric with hot water. Energy will cost less as less electricity will be used.
  13. Are you saying pipe outgoing hot of pv into incoming cold of electric?

    This isn't getting inspected but I'm pretty sure code wouldn't allow that setup, or at least, kill the warranty on the new electric heater since it's going against the intended setup.


    Maybe a diagram?
  14. BAPlumber

    BAPlumber Plumber

    Messages:
    227
    Location:
    Vashon, Washington

    I personally don't know of any code that dictates the incoming temp for a water heating system, other than the manufacturer limits. I don't believe an electric tank cares what temp the incoming water is. It just heats to it's thermostat.
  15. GrumpyPlumber

    GrumpyPlumber Licensed Grump

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    Location:
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    Rugged, BobNH nailed it, thats what I'd do...no easy way to balance two tanks set up parallel, BAPlumber makes sense too...not aware of any warranty that doesn't allow it...but you want to read the fine print.
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