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Thread: Hot water expansion tank

  1. #1
    DIY Senior Member Mikebarone's Avatar
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    Default Hot water expansion tank

    I have a client that has a home that has two electric hot water tanks. One tank does one half of the house, and the other tank does the other half of the house. Recently, she had a plumber install a pressure reducing valve on her house and, (because of what I’ve learned on this great forum) she now has a closed system and she needs an expansion tank. The PRV is set at 60 psi. My question is, do I need to install two expansion tanks, (one for each hot water tank) or could she get away with just one tank on the incoming cold water line, (after the PRV) like by her water softener?

    Thanks all,

    Mike

  2. #2
    In the Trades Gary Swart's Avatar
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    One tank would be sufficient, but I would opt for the larger size. Install it between the PRV and the first water heater.

  3. #3
    DIY Senior Member Mikebarone's Avatar
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    Default Thanks

    Quote Originally Posted by Gary Swart View Post
    One tank would be sufficient, but I would opt for the larger size. Install it between the PRV and the first water heater.
    Thanks Gary. The Home depot by my house only sells one size, (ie one tank for one hot water tank). I will get on the web site that makes the tank, and see if I can get the next size.

    Thnaks again,

    Mike

  4. #4
    DIY Senior Member construct30's Avatar
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    Default

    I would just watch the price with shipping, it might be cheaper to go with the two expansion tanks. Also size does matter so be sure you get them to size it if you order one.

  5. #5
    Retired Defense Industry Engineer jadnashua's Avatar
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    I think it is Watts that has an expansion tank size calculator on their website. You enter the size of the WH(s), the expected temperature rise, and it tells you what size tank you need. They usually come precharged with 40# in them, if your PRV is set to 60, you'll need to add some air to it.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  6. #6
    TROJAN WORLDWIDE SALES RP MACPLUMB 777's Avatar
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    Default Hot Water Tank



    You need two expansion tanks, one on each water heater,
    BETWEEN THE COLD SHUT OFF ON EACH HEATER ! ! !
    otherwise the tank can be isolated by any shut off's in system,
    and still pressure bulge or blow up without expansion protection

    JERRYMAC MASTERPLUMBER
    PH.D WATER HEATEROLGY ! !

  7. #7
    Master Plumber Redwood's Avatar
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    Our resident PH.D Waterheaterologist is correct! I was scrolling down to post the same thing when I saw his post.

  8. #8
    In the Trades Gary Swart's Avatar
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    Thank you for that information Dr. Jerry Mac. I stand corrected.

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    DIY Senior Member Mikebarone's Avatar
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    Default All good points...thanks!!!

    As usual, I want to thank everyone for all of the great inputs. I tell everyone how great this forum is. You all make this handyman look somewhat intelligent….LOL!
    This poor lady’s house was build by her ex-husband, and you wouldn’t believe some of the, “short cuts” I’ve found in the past three years I’ve been working for her. The first day I went to work for her, I was just going to replace a bad started switch on her outside stainless steel BBQ. After I noticed that the back of the switch was melted, (and I found that three of the six gas valves were leaking), she had me there for a total of 12 hours that day fixing other things…LOL…and I’m not done yet!

    Thanks all again,

    Mike

  10. #10
    Plumber Cass's Avatar
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    According to the Watts info here

    http://www.watts.com/pdf/ES-PLT.pdf

    The Watts PLT-12 (large tank) will handel up to 120 gallons being heated / expanded at a water pressure of 60 PSI.

    2 expansion tanks is a good idea but not necessary, I have been in very few homes that have a valve between the main and the water heater or heaters valve.

  11. #11
    Moderator & Master Plumber hj's Avatar
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    Default heater

    otherwise the tank can be isolated by any shut off's in system,
    and still pressure bulge or blow up without expansion protection

    If that did happen then she also had a defective, nonfunctional temperature/pressure relief valve, AND if so, and conditions were such that a blow up could occur, all the expansion tanks in the world would not prevent it.

  12. #12
    TROJAN WORLDWIDE SALES RP MACPLUMB 777's Avatar
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    Default Hot Water Tank




    It's called murphys law ! !

    it should be installed between cold shut off and tank,

    if do'es not have this protection voids MFG'S warrenty on leaking tanks



    JERRYMAC MACPLUMB 777

  13. #13
    DIY Senior Member Mikebarone's Avatar
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    Quote Originally Posted by MACPLUMB 777 View Post



    It's called murphys law ! !

    it should be installed between cold shut off and tank,

    if do'es not have this protection voids MFG'S warrenty on leaking tanks



    JERRYMAC MACPLUMB 777
    Good point!!!

    Thanks, Mike

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