Hot water recirc question

The Tank Hot water recirc question

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  • #21109
    bilug
    Participant

    I have a question about a hot water recirc loop. Hopefully this makes sense…

    I have an existing 120gallon tank, with 2″ cold pipe in, 2″ cold pipe out and dedicated recirc pump and 3/4″ line on the 2nd floor of a building.

    I need to move the water heater out of the existing room.

    Rather than move the tank and repipe everything to a new location (~$18,000 bid!!!) we decided to use an existing water heater on the first floor that serves the general building fixtures.

    We placed a T on the 1st floor water heater, ran PEX up to our 2nd floor hot water lines and tied them in. We cut the cold, hot and recirc lines going to the 2nd floor water heater and capped them.

    All good…we have good pressure and flow from the hot tap at all locations now on the 2nd floor.

    However – now we need to add a recirc to get hot water at the tap in a reasonable amount of time.

    We are looking at placing a recirc pump under a sink and tying the hot to the cold…pretty standard practice. The Redytemp TL5000N should do the job.
    However – we know that our cold line does not return to the 1st floor tank —-so where does the water go? I know the pump will pull the hot water up – but I’m not clear on where the cold water will get recirc’d to.

    Thanks!

    #21110
    energyexpert
    Participant

    Draw a one line diagram of the cold line from the sink with the proposed recirc pump back to the point where the first floor water heater tees off for its supply. This will be your flow path. Just be sure there are no check valves in the line.

    David

    #21111
    bilug
    Participant

    energyexpert wrote:

    Draw a one line diagram of the cold line from the sink with the proposed recirc pump back to the point where the first floor water heater tees off for its supply. This will be your flow path. Just be sure there are no check valves in the line.

    David

    But I fear that is my problem David – I believe the whole 2nd floor water supply (cold) is fed through a backflow preventer.

    I have to trace the line to find out if another path exists. If it doesn’t – what happens? Seems like it would just pressurize the cold line until it bursts at a weak point.

    #21112
    energyexpert
    Participant

    What is the reason for the check valve at that point? If there is not a real reason (ie, just because someone thought a check valve should be there), take the guts out of the check valve or replace it with a ball valve or pipe.

    Unless you have a powerful positive displacement pump, you will not blow up anything. But you could damage a pump by dead heading it.

    David

    #21113
    bilug
    Participant

    It’s a full blown backflow preventer that gets tested yearly. I can’t remove that!

    I think they have the water to the building coming in a main on the 1st floor – then it branches off to different areas of the building. The cold line that serves my 2nd floor comes in via a backflow preventer. If I shut the valve at this point, my whole cold water on the 2nd floor goes down.

    #21116
    energyexpert
    Participant

    I would revisit the plumbing code and see if the second floor check valve is required. The code may require testing the valve yearly because it is installed. But is it required (and why) to be there in the first place? Usually one check valve where the water enters a building is sufficient to prevent anything getting back into the supply system.

    David

    #21117
    bilug
    Participant

    Thanks for the info. I’ll ask why it’s there next time they come to test…good point about only needing one on the main coming in.

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