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Thread: Water Heater Temp

  1. #1

    Default Water Heater Temp

    I have a 50 gal electric water heater and my temp on my water heater is set to 130 deg and it seems that there is enough hot water for no more than 3 showers. Once the 4th person takes a shower, you have no hot water left. Should I increase the temp or it wont matter?

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    If you have a teenager, you might run out after one shower!

    A new showerhead can't legally be sold that uses more than 2.5gpm. So, how long are those three showers and how old is the showerhead? You might want to run it into a bucket while timing it to see what you have. You can't get 50-gallons of 130-degree water out of the tank, as the incoming cold dilutes it. Figure anything over 70% a bonus.

    Yes, you can effectively make the tank look bigger if you raise the temp, but for safety reasons, you should also install a tempering valve to limit the output. They're required where I live. Basically, it's an adjustable valve that mixes some cold with the hot let and 'tempers' it so it isn't quite as hot...it's like mixing the cold at the shower, but done at the outlet of the tank to help prevent excessively hot water from harming someone.

    Last edited by Terry; 08-06-2011 at 01:25 PM.
    Jim DeBruycker
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  3. #3

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    Both bathrooms have new showerheads that my wife bought at Bed Bath and Beyond within the past year.

    What's the logic in making the tank look bigger if you raise the temp?

    Is setting it to 140 degrees OK?

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    Illinois Licensed Plumber SewerRatz's Avatar
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    Quote Originally Posted by Mikeyboy View Post
    I have a 50 gal electric water heater and my temp on my water heater is set to 130 deg and it seems that there is enough hot water for no more than 3 showers. Once the 4th person takes a shower, you have no hot water left. Should I increase the temp or it wont matter?
    Turning up the temp of a water heater, you run the risk of scalding. Gamma and the water heater manufactures recommend you do not have the temp any higher than 120 degrees. A low flow shower head can help a lot and shorter showers is a huge help too.

  5. #5

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    So, what's the best way to allow more people to take showers with hot water?

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    Illinois Licensed Plumber SewerRatz's Avatar
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    Quote Originally Posted by Mikeyboy View Post
    So, what's the best way to allow more people to take showers with hot water?
    A larger heater, a lower flow shower head, shorter showers, or even add a second water heater. Two 50 in series would give you a lot of good hot water.

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    Master Plumber Redwood's Avatar
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    Quote Originally Posted by Mikeyboy View Post
    What's the logic in making the tank look bigger if you raise the temp?

    Is setting it to 140 degrees OK?
    It's all about BTU's The higher the temp of the water stored in the tank the more heat you have stored.

    You then will mix more cold and less hot so you will in effect be "Making the water heater look bigger."

    The problem is that this hot water presents a very real danger of scalding someone. Especially young and elderly people! 3rd degree scald injuries occur in about 1 second at 160F, 5 seconds at 140F, 9 minutes at 120F, 6.7 hours at 110F. Scald Information click here

    The water must be tempered to a safe temperature as it leaves the water heater when elevated temperatures are used. One of the valves pictured below would be required. Watts 70A & L70A Tempering Valve click here

    Last edited by Redwood; 01-22-2009 at 09:15 PM.

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    Plumber jimbo's Avatar
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    There is the 70% principal in action here. A water heater will deliver 70% of its gallon capacity, at "shower" temperature, that is within about 20 f set point. SO, you 50 gallon tank will give you 35 gallons. ~2 gallons per minute, 10 minute shower....20 gallons. You are lucky to get 3 showers, and you can just forget 4!

    There are remedies, and they have been described in the posts above mine.

  9. #9
    Extreme DIY Homeowner Scuba_Dave's Avatar
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    My 50g electric indicates that it can provide 58 gallons of hot water in the 1st hour. At 20g a shower then the 3rd shower would start to go cold. I think this also depends upon how hot you like the shower
    DIY Handyman (not 4 hire)
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  10. #10
    Illinois Licensed Plumber SewerRatz's Avatar
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    Quote Originally Posted by Scuba_Dave View Post
    My 50g electric indicates that it can provide 58 gallons of hot water in the 1st hour. At 20g a shower then the 3rd shower would start to go cold. I think this also depends upon how hot you like the shower
    Well in todays code for residential the showers are supposed to have a temperature stop built in and set to no higher than 115 degrees, and for public showers they should be set to 110 degrees. So I bet they are using the 110 degree mix to say you would get that much out of it.

  11. #11
    Retired Defense Industry Engineer jadnashua's Avatar
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    The point is, if at the tank, the water was say 160-degrees, then you mixed it with enough cold to get 120-degrees out, on that hot water supply line, for every 1-gallon of hot, you might get 1.25-gallons (or more depending on how cold the cold is and the dilution factor) at 120-degrees. You aren't emptying the WH as fast because you are mixing in more cold to the now very hot water. So, effectively, the tank 'looks' bigger. To be safe, you must temper it at the tank, rather than doing it at the shower, since if someone accidentally used all hot, they could get injured quite quickly. The higher the differential between the tank and the room, the faster it will leak heat (i.e., cool off), so your efficency will decrease some, but maybe not as much as adding a second tank which would have much more surface area to dissipate heat. Since you'd be working the tank harder, it may not last as long.
    Jim DeBruycker
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    Remodel Contractor GabeS's Avatar
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    Is installing a mixing valve a widely accepted practice? Is it up to code? Are there any precautions that need to be taken?

    I'm assuming the knob on the valve controls the amount of cold water entering the mixture. Is that correct?
    Gabe

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  13. #13
    Illinois Licensed Plumber SewerRatz's Avatar
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    Quote Originally Posted by GabeS View Post
    Is installing a mixing valve a widely accepted practice? Is it up to code? Are there any precautions that need to be taken?

    I'm assuming the knob on the valve controls the amount of cold water entering the mixture. Is that correct?
    Here is the Illinois code say so on using mixing valves if the temp is set higher than 120 at the heater.

    A) A thermostatic mixing valve, conforming to ASSE 1017-1999, shall be installed on the hot water line to the plumbing fixtures. (The mixing valve shall be set to prevent temperatures exceeding 120F from reaching the plumbing fixtures.)

    B) A single check valve shall be installed in the cold water line supplying the water heater. (This will prevent hot water backing up from the heating unit to the plumbing fixtures.)

    C) A properly sized and approved expansion tank shall be located on the outlet side of the check valve in the water heater's cold water supply with no shut-off valve between the heater and expansion tank.

  14. #14
    Retired Defense Industry Engineer jadnashua's Avatar
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    As I said before, my city REQUIRES a tempering valve to be installed on any new (as of 4-5 years ago) WH replacment or original installation. So, yes, they are fairly common. It's another thing to fail, but they are pretty reliable.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  15. #15
    Remodel Contractor GabeS's Avatar
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    OK. Understood. What I don't understand is when is a expansion tank required to be installed for a water heater?

    I guess in Illinois that was one scenario, where mixing valve is installed with temps above 120 degree. When else is one required? Virtually all water heaters that I see have no expansion tanks. Only boilers.
    Gabe

    Don't follow my advice, I only know a thing or two about a thing or two.

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