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Thread: Installing 1/2" NTP Grundfos recircultion pump on 3/4" NPT Water Heater

  1. #1
    DIY Member CountryBumkin's Avatar
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    Default Installing 1/2" NTP Grundfos recircultion pump on 3/4" NPT Water Heater

    I bought a Grundfos recircultion pump (model UP10-16BN5/ATLC) to reduce the time it takes to get hot water to the shower on the far side of the house. The plan was to install the pump in-line on the water heater outlet and the "confort valve kit under the sink in the bathroom.

    What I just noticed is that the pump I bought has 1/2"NTP fittings and my water heater has 3/4 NTP inlet/outlets. The piping into and out of the water heater is about 24 inches of 3/4 copper transitioning to 3/4 " PB where it goes into the wall. I don't know where the 3/4 pipe ends in the wall and the 1/2 PB starts, but I have not seen 3/4 piping anywhere in the house. Regardless, I'm concerned about restricting the volumn of hot water if I install the pump in-line as designed.

    My question is: 1) should I install the pump in-line in the 3/4" water heater outlet (which will/may reduce the flow) and not worry about it; or 2) should I try to return the pump (unlikely to get full refund) and buy a pump with 3/4" fittings; or 3) is there something else I can do?

    Thanks

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    Do you have a dedicated return line? If so, you could put the pump there as the size wouldn't be an issue.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3
    DIY Member CountryBumkin's Avatar
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    Thanks for your reply.
    I could run a dedicated return line. If I'm understanding the term properly. When I rebuilt my master shower/bathroom I converted the hot and cold PB lines coming out of the slab to PEX ran them up into the attic and looped them back down to the shower valve. I figured if the PB ever failed in the slab I would be able to cut the line in the attic and convert to PEX from there. So I could cut the hot water line in the attic (cap the PB side) and run a new line back to the water heater (probably 60 feet) - where I guess it would then tie into the recicultation pump (Tee'd into the water heater 3/4 line). Is this what you meant?

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    Test, Don't Guess! cacher_chick's Avatar
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    IMO, the 1/2" recirc is commonly installed with a dedicated return line pumping water from the bottom of the water heater at the drain port.
    Last edited by cacher_chick; 04-20-2011 at 04:18 PM.

  5. #5
    Retired Defense Industry Engineer jadnashua's Avatar
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    Just like the name implies, recirculation requires a loop. You either make the cross-over to the cold line, and use that to pump the water back around or create a dedicated line back to the WH (and inserting it into the bottom of the WH is the common solution). When you use the cold line to create the loop, it becomes warm. WIth a dedicated return line, the cold stays cold. So, if you put a T on the hot line, and ran a new line back to the WH (1/2" would be fine), and removed the drain valve on the bottom of the WH so you could add in a T to receive the return line, and then reinstall a drain valve, you'd be nearly there. You'd need a checkvalve somewhere in that loop.

    And, depending on the layout, you might find that the water would circulate by convection, without the use of a pump at all with a dedicated return (you'll still need a check valve).
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    Moderator & Master Plumber hj's Avatar
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    You must be trying to make a "Do it yourself" circulation system, because the Grundfos "Comfort" pump IS 3/4" and it has a female "swivel union" inlet to fasten directly to the hot water outlet and a 3/4" male outlet to reconnect the outlet pipe to it. With ANY piping below the water heater's outlet, a gravity system would not operate.

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