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Thread: New Water Heater-Cost to Operate

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    Default New Water Heater-Cost to Operate

    I was looking at new electric water heaters on the Home Depot site. Of course they have all sizes with variable warranties. It also list the yearly operating cost for each model. The 6 and 9 year warranty models both have dual 4500 watt elements. The 12 year warranty models all have dual 5500 watt elements. All of them with the larger 5500 watt elements had a lower yearly operating cost. Is that because the more wattage heats faster than the 4500 making them cheaper to operate? I figure also the 12 year models are more insulated than the 6 and 9 year models. So would it be the bigger element or the more insulation that makes it more efficient or a combination of both? I just always figured the 5500 watt units would cost more to run but I guess I was wrong.

    I keep my WH set at 140 because I feel like I am using less hot at 140 than when on 120.(other than washer FL or DW) When I had it on 120 I used more hot and less cold in the shower and sinks. At 140 I add more cold so I am using less hot for the same uses. Maybe this isn't right either but it just seems that way to me.

  2. #2
    DIY Senior Member Reach4's Avatar
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    Quote Originally Posted by prd823 View Post
    So would it be the bigger element or the more insulation that makes it more efficient or a combination of both?
    Just the insulation.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Watts are watts...it takes a certain amount to heat the water (bigger elements can reheat it faster, that's all), it doesn't matter the size of the elements...as said, for the same size WH, either the shape or the amount of insulation can make a difference on how much heat is lost to the room. It comes down to surface area and how good the insulation is.
    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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    In the trades Dana's Avatar
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    Keeping the storage temp at 140F is less efficient than keeping it at 120F, due to the higher temperature difference between the water and the room too.

    If the water heater is in a 70F room that's a difference of (140F-70F=) 70F instead of (120F-70F=) 50F. Reducing the temperature to 120F is the equivalent of adding 30% more insulation to the tank from a standby loss point of view.

    Keeping it at a higher also means that the hot water abandoned in the plumbing between draws is also at a higher temperature, increasing the distribution losses, unless you're mixing it down to 110-115F right at the tank.

    Yes, by keeping it at 120F you use more hot water (volume), but not more heat (BTU) when mixing down 140F. Unless you can't quite fill your biggest tub with the hot water tank set at 120F, keeping it there is generally safe, and uses less electricity. Dropping it lower than 120F by very much can put you in the Legionella sweet spot, but Legionella colonies can't grow at 120F, even though it doesn't kill already established colonies.

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    Master Plumber master plumber mark's Avatar
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    Why not just spend another 15 bucks and install a water heater blanket on the heater
    and save up to %25 of your water heating bill??

    then set the heater at 135 which will kill off
    anything tha t lives in the tank

    you are all forgetting about stratification, and its better to find
    a sweet spot around 135 , not too hot and not too low....

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    In the trades Dana's Avatar
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    Except that 135F isn't hot enough to actually kill off an established legionella colony, there's nothing wrong with adding cheap insulation on the hot water heater to limit standby losses. It's still best to temper it to something under 120F before the hot water distribution plumbing though. (And required under current code for distribution plumbing feeding sinks/shower/tubs, but not clothes or dish washers.)

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