Electric Water Heater 30 or 40

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by jimqual7, Jul 25, 2008.

  1. jimqual7

    jimqual7 New Member

    Messages:
    1
    I currently have a leaky 40 gallon electric water heater in excess of 15 years old. It only supplies the master bedroom suite. 2 showers every morning in an hours time. Rest of the time it is idle except for sink use.
    What is the smallest heater I can get away with and would the savings be significant enough to possibly sacrifice the loss of hot water during a shower?
    It is glass fiber insulated. I'm sure that todays insulation is also more efficient. The way I figure it, even if I went with another 40, it would still be cheaper to run than the 15 year old model.
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,832
    Location:
    New England
    You only get about 70% of the WH contents before it cools off a lot from the incoming water. So, with a 'normal' showerhead at 2.5 gallons/min, that's only about 8-minutes, depending on how hot you run the heater - you'd get longer as you turn it up. That's enough to get clean, but not enough to relax much or sooth some sore muscles.

    If you do run the thermostat up high (it has some benefits - you won't grow nasty things in the WH), then you should install a tempering valve to limit the max output so someone doesn't accidentally scald themselves.

    Efficiency of the burners probably isn't all that much different, but insulation may be better on the new units.

    There are some that are more efficient than others.
  3. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    Electric water heaters are near 100% efficient....all the energy goes into the water. SO it doesn't matter what size the tank is, if you take a 20 gallon shower, you have to reheat 20 gallons. The storage losses are minimal. A 30 gallon tank will probably be stretched to give 2 people a shower. And it probably costs almost the same as the 40 gallon job.
  4. Redwood

    Redwood Master Plumber

    Messages:
    7,453
    Location:
    Connecticut
    Last I checked here the supply house was charging less for a 40 gal water heater than a 30. Really the 30 is too small in so many applications that they sell very few of them so they charge more for them. In fact there is one supply house that charges less for a 50 than a 40!:eek:
  5. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,315
    Location:
    Cave Creek, Arizona
    heater

    Economies of scale dictate that the heaters that have the least demand cost more. Even a 2 gallon heater costs as much, or more, than a 40 gallon one. The only difference between ANY residential heater is the storage capacity. If you only need a little bit of hot water at a time, a 30 will be adequate. If you need a lot of water all at once, you need an 80 or 100 gallon tank. But the time it takes to reheat the water you use will be the same on a per gallon basis, i.e., if you use 30 gallons from an 80 gallon tank it will take the same amount of time and electricity as if you used the entire contents of a 30 gallon tank.
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