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Thread: 2 HW Tanks in Parallel, Where to Tap Irrigation Line? Need for Expansion Tanks?

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    DIY Member jluksic's Avatar
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    Default 2 HW Tanks in Parallel, Where to Tap Irrigation Line? Need for Expansion Tanks?

    I have 2 50 gallon HW heaters in Parallel. I have tapped into the cold supply line that feeds the 2 HW heaters between the HW heaters.

    See diagram.

    I have noticed that the cold water line supplying "Tank B" gets very warm over time.

    Questions:

    1. Where is the proper place to tap into the cold water lie to feed my irrigation system? Before, during or after the 2 HW heaters are served?

    2. The "excess" heat generated by my HW heaters seems to "back track" into their respective cold water feeds... will an expansion tank address this issue? If so, where should the tanks be located?

    Thanks.
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    In the Trades Gary Swart's Avatar
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    I would tee off of the main line prior to the water tanks for the irrigation. Right after the tee, install a stop-n-waste to be able to shut the irrigation off without disrupting the rest of the water system. After the shut off valve, you must use a backflow preventer to avoid the chance of contaminating you domestic water supply.

    An expansion tank is needed if you have a pressure reducing valve (PRV) as that creates a "closed" system. The PRV prevents the expansion from being absorbed by the water main and results in a tripped TP valve on the water heater(s). So unless you install a PRV, there is no need for an expansion tank.

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    DIY Member jluksic's Avatar
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    Just curious but why would I tee off the main "prior to the water tanks" as opposed to after, or inbetween (my current setup)?

    As for the expansion tanks... if I was to install expansion tanks prior to the water tank supplies, would the expansion tanks take care of the hot water being forced back into the cold feeds?

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    In the Trades Gary Swart's Avatar
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    1. If you don't tee there, your backflow will not protect the entire system.
    2. Yes, but it's hardly necessary.

  5. #5

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    Isn't it normal for the cold inlet line to get warm if the tank is just sitting there and not being used? I had a hot water leak once, and the way it was diagnosed was because the cold inlet was always cold--meaning there was constantly new water running through the line. Not to mention a giant gas bill at the end of the month.

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    In the Trades Gary Swart's Avatar
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    Yes, the heat will transfer back into the cold intake line, but that's not what an expansion tank is for. An expansion tank handles the expanded hot water that backs into the cold intake IF there is a PRV in the system that prevents the expanded water from being absorbed by the entire water system including the city mainline.

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    DIY Senior Member Phil H2's Avatar
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    jluksic,
    Are the water heaters connected in parallel or do the hot water heaters supply differnet fixtures. If they are connected in parallel, the piping is balanced so each heater has an equal flow through them. In this arrangement, when your irragition is running, the left water heater will do all of the work. But, your picture makes it look like the heaters are supplying seperate fixtures.

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    Master Plumber master plumber mark's Avatar
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    Talking why by the water heaters

    What in the world possessed you to mess with your parrellel system for the water heaters in the first place?? Why would you want to tee off there for your iragation system>??

    you are just gong to mess up y our hot water flow this way
    and you are probably already drawing off mostly one of the tanks and the other is now 90% sitting dormant....


    You should keep away from them and cap off that line you tied in and then do what the other person mentioned and tie into your line near where it comes into your home......




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    DIY Member jluksic's Avatar
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    The 2HWHs were in parallel when I bought the house. And yes, the tanks feed different fixuters as "Phil H2" deduced - which I guess dosen't make this a true parallel system.

    With a little work, I can plumb the 2HWHs in series and change the irrigation tap location closer to where the main line enters the house.

    Please please please - I'll take all your "2HWHs in Series" tips!

    Thanks,

    Joe

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    Moderator & Master Plumber hj's Avatar
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    Default heaters

    [quote=jluksic]The 2HWHs were in parallel when I bought the house. And yes, the tanks feed different fixuters as "Phil H2" deduced - which I guess dosen't make this a true parallel system.

    With a little work, I can plumb the 2HWHs in series and change the irrigation tap location closer to where the main line enters the house.

    You do not have a parallel system, you have two separate systems, and unless you are having a problem with them there is no need to change them. Tap the irrigation system anywhere you want to. The little bit of convected hot water will be flushed from the system immediately when the irrigation valve turns on, and the required vacuum breaker will be on the line to the irrigation system so it will do its job no matter where the connection is made.

  11. #11
    DIY Member jluksic's Avatar
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    I understand that my setup is not a true parallel system. The problem (as I haven't done a great job to describe) is Tank B only feeds a basement bathroom not used very often and the Tank B cold supply gets very very hot. Futhermore, when I turn on my sprinkler system, there seems to be a lot of hot water running through the pipes - and I'm not just tlaking about the hot water that have moved into the pipe due to convection. It's almost like the water heater is sending it's hot water supply through the cold water feed into the irrigation line... like there's some sort of siphoning going on due to the massive amount of water hater in Tank B that's looking for relief. You guys must think I'm nuts.

  12. #12
    Moderator & Master Plumber hj's Avatar
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    Default tank

    Not nuts, but siphoning can only occur if their is no pressure in the tank and the other end of the system is open so air can enter as you suck water out the other end. (In reality it is not really sucked out, the incoming air pushes it out, but that is what seems to happen.) Unless your drawing is incorrect, the only hot water would be the convected amount. The water does not build up pressure trying to get out of the tank, like some caged animal.

  13. #13

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    Just out of curiosity, have you tried lowering the water temp. of tank B? Maybe there's something wrong with the thermostat and the water is scalding hot. Have you tried turning off the water inlet valve to tank B? If that solves your problem, you can leave B shut down until you need to use the basement bathroom.

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    Plumber Cass's Avatar
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    Do you have a check valve and / or pressure reducing valve in line where the water line enters?

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    DIY Member jluksic's Avatar
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    I have a CSV before my pump tank.

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