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Thread: replace gas with electric water heater

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  1. #1
    DIY Junior Member young707's Avatar
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    Default replace gas with electric water heater

    I have a leaking 40 gallon 40000 BTU/hr gas water heater in garage open area, at home for 2 adults in San Jose, CA.
    I am looking into to replace with 40 gallon 4500W electric water heater.
    So I need to run 220AC extension for around 5 feet, wall socket, and breaker. I also like to add shut off timer so that I only run the heater 12 hours instead of 24 hours every day. So far, I do not find this timer at Home Depot.
    What kind of work time and approximate cost for electrician to do this work?

  2. #2
    In the trades Dana's Avatar
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    Replacing it with another gas HW heater would have far lower operating expense than an electric HW heater in your area (unless you went with a heat-pump hybrid type at much bigger upfront expense, in which case the operating costs might be comparable.)

    Turning off an electric HW heater for 12 hours/day with a timer has almost zero impact on the amount of power used. Electric tanks have very good insulation and very low standby loss. To get a significant reduction in standby loss and savings would require a big drop in the water temp during the "off" period, but an electric tank set to ~125F would typically lose less than 1/4 degree per hour, so you'd still be over 120F at the end of your 12 hour period. The vast majority of the power use is for raising the 55-65F incoming water up to the 120F-140F setpoint temp- the difference in standby power use between water with less than a 5F average difference is truly in the statistical noise- low single-digit percentage savings on the overall power use at best. Only if you can get a rate reduction on your electricity bill for heating water only during off-peak hours would a time-of-day approach make any economic sense.

    Whatever heater you install, you get pretty good payback on 5/8" wall closed cell pipe insulation on all the near-tank plumbing (including the first 6-10' of the cold-feed closest to the heater and the temperature & pressure overflow valve & outflow plumbing), as well as any hot water distribution plumbing that is accessible. For a primer on how to do it, see: http://www.leaningpinesoftware.com/h...er_pipes.shtml

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    DIY Junior Member young707's Avatar
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    Dana, Thank you. Please help me with rough estimate comparison between gas & electric water heater.
    In San Jose area, 2 adults, single family home, hot water usage is roughly around (shower + faucet + dish washing + laundry ) 32 gallons per day, is this number close, or I should use half for heated water?
    How much cost between gas & electric water heater operating cost?

    So, in this areas, you think 12 hours shut off timer will not save much in energy?

  4. #4
    Retired Defense Industry Engineer jadnashua's Avatar
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    Shutting off an electric WH via a timer will cost more to install than you'd likely ever recover...it just doesn't cost much to leave it on. With the insulation, with no use, the tank just doesn't cool off enough to require it to turn on much (if at all) during that 12-hour period. Now, if you lived in say northern Minnesota and had the thing in a garage that got to just above freezing most of the winter, that's be another issue, but then, if you did turn it off, it would likely freeze the lines!

    1KwHr = 3400BTU
    1 Therm of NG = about 100,000BTU

    Now, the NG WH isn't as efficient as electric, but say the electrical unit ran for 1 hour/day = 40000/3400 = 11.76KwHr.

    If the NG WH had to run an hour, with the same sized burner, it would use about 1/2 a therm - giving that it isn't as efficient as electric. Some designs are better, some are worse.

    Price your electric and NG and you can get your localized numbers. Around here, that 11.76KwHr would cost around $2.11 verses a 1/2-therm of NG for about $0.75. Do you really want an electric WH? If you had to run a new gas line or even start up a new service, that initial installation cost could be quite a bit, but since it's already there, it rarely is more cost effective to go electric when NG is present.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Junior Member young707's Avatar
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    understand.
    So you are saying, given same amount of heated water, electric will cost 3 times more compare to gas, correct?

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    Retired Defense Industry Engineer jadnashua's Avatar
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    That's true where I live, but we have high electric rates...your results may differ. You can easily tell by looking at your bills and comparing. Plus, typically, a NG WH will have a quicker recovery rate, and if you do need even faster recovery, you can get one with significantly larger burner. A larger burner just needs to run less time - that doesn't mean it uses more (although it may, but it's not linear). Whle you may not use a lot of hot water, a fairly typical use pattern is lots all at once...the same sized electric may not be large enough as a NG one. Having more available, though, may tempt you to use more.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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