Dhw recirc check valve

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by DIYorBust, Oct 7, 2020.

  1. DIYorBust

    DIYorBust Active Member

    Joined:
    Mar 5, 2019
    Location:
    Long Island, New York
    Can anyone recommend a good brand or style of check valve for a dhw recirce system? I'm looking to do two branches with 2 check, plus a check at the pump. I also need two globe valves for balancing I'd love recs on. Thanks in advance!

    Diy
     
  2. DIYer123

    DIYer123 New Member

    Joined:
    Jan 16, 2016
    Location:
    Massachusetts
    Do you need check valves? Do you want to prevent draining down stream of the check for service? Many people and even some engineers think check valves somehow ensure direction of flow but they are really only preventing back-flow. Only thing that ensures flow is a difference in pressure, all fluids flow from high Pressure to low pressure . Check valves will also just add pressure drop, meaning energy loss and have a chance to fail and dead head your pump. But again you may have service reasons for it. I would recommend a swing check in the horizontal or spring check in vertical just make sure the opening pressure is well below the pump discharge pressure. As far as globe valves Is the circ system a on demand / timed circuit or an always on? If it is always on I would recommend a thermostatic balancing valve, just install one in each of the return lines and your good. I recommend a product called CircuitSolver. I have installed countless in food manufacturing facilities on hot water systems to ensure hot water is available in the prescribed time at hand wash sinks, far easier then manually balancing with circuit setters or manual valves. And even with 30 sinks no need for a single check.

    A system diagram of what you are doing would help.
     
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  4. DIYorBust

    DIYorBust Active Member

    Joined:
    Mar 5, 2019
    Location:
    Long Island, New York
    Here's a quick sketch of what I'm trying to build. The fixtures are already plumbed, its only the recirc line I'm installing. Also the hot water heater has a thermostatic mixing valve, but I need to move the water heater soon so I will probably redo the setup there, so I didn't show it clearly here. Do you think the circuit solver would work? The pump will run only in the morning and evening rushes, so if I eliminate the check valve I worry it will take twice as long to get hot water at the remote fixtures with the water running through two lines. What do you think I could do better?

    Thanks!
     

    Attached Files:

  5. DIYer123

    DIYer123 New Member

    Joined:
    Jan 16, 2016
    Location:
    Massachusetts
    Below is what I would do assuming you have two branches. I would skip the circuit solver and just put a ball valve on the shorter run, but if you didn't want to adjust the system, the solvers are nice. What will happen is when the pump kicks on both solvers will be fully opne and teh moajoity of teh hot water will quickly flush the short run until it gets up to temp and the circuit slaver closes down which will force the majority of flow into the long run. WIth the ball valve you would just turn on the pump and close the ball valve until you get the line to clear in about equal time. It will take quite a few attempts and then waiting for it to cool back down.

    I would recommend the one check valve at the cold water supply to the heater so that you don't force hot water backwards in the cold water line. If the pump is running and someone opens a cold water tap before the water heater it will push water backwards (if there is a cold tap belfre the heater)

    All the ball valves are purely recommended for service (minus the one if you choose to balance with one)

    The pressure regulator and gauge are an optional and recommended if you have high water pressure as the circ pump will add its discharge pressure to the city / supply water pressure meaning if you have high pressure already you may end up with too high of pressure and could cause issues with piping / fixtures down the road


    HW circ.jpg
     
  6. DIYorBust

    DIYorBust Active Member

    Joined:
    Mar 5, 2019
    Location:
    Long Island, New York
    I this all makes sense, and thank you for the diagram, this makes it very easy to understand. I think my biggests concern, is that the pump will only run a few hours a day, and the short run is not that much shorter than the long run. the short run may be 35-45 feet, the long run about 75 feet. So with no check valve, the fixtures on the long run will pull water through the return line and take even longer than they already take, which can be over 3 minutes.

    However I see now that the check valves come with their own issues. If hot water was run in the short line, it may be very close to a fixture in the long branch, but it still needs to pull water all the way around. I also worry with a manually balanced valve, this would be worse, since the pump will detect hot water in the return line if someone used the short branch first.

    Do these concerns seem valid?

    Thanks!

    DIY
     
  7. DIYer123

    DIYer123 New Member

    Joined:
    Jan 16, 2016
    Location:
    Massachusetts
    I assume you by above you plan on running the pump on a timer at major use times ie something like 6 am to 7 am and 7 pm to 8 pm? or are you planning some other type of control?

    I ask because it seem like you want to re-circ to make sure the water is hot when you need it but you are worried on how long it will take to clear which is not an issue if you time it so the water is hot already in the loop because its re-circed.

    If you are thinking you want a recirc to kick on only when a fixture is on this is not how a recirc typically works and you are correct adding pipe volume of cold water will not help. Adding a check would prevent the condition you talk about but it should never be an issue if you are running the rec-circ and the loop is hot. You would get the same result of the check valves if you just added the pump and didn't pipe the recirc, it would just act like a booster pump which may help if you root cause of slow water is low pressure / flow.

    Or are you worried about the off peak times when the pump is not running?
     
  8. DIYorBust

    DIYorBust Active Member

    Joined:
    Mar 5, 2019
    Location:
    Long Island, New York
    Thanks, what you're saying I do agree with completely, while the pump is running, everything will work great without the check valves. But as you point out, I'm concerned about the off peak times when the pump is not running. It's not worth running the pump 24 hours for occasional use, but from a practical perspective I don't want to have to wait 5 minutes for hot water. This is a three unit building. I am only running the circulation up to the 2nd of 4 floors, but that would probably decrease the wait time from 3+ minutes less than one minute at the top unit.
     
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