GPM for dedicated recirculation line.

Discussion in 'Tankless Water Heater Forum' started by Monguila, Mar 28, 2021.

  1. Monguila

    Monguila New Member

    Joined:
    Feb 4, 2021
    Location:
    Vista, CA
    Good day everyone. I read somewhere that the GPM on a dedicated 3/4" return line should not exceed 1 GPM. Is there any validity to that statement? My return line is at 4.7 GPM.

    The total length of the line is +- 120 linear feet, connected to NPE210A. 80% of it is a straight shot along the house. Then, into the garage, up, across, and down to the WH. The line originated from a 1/2" pipe but immediately upsized to 3/4 CPVC.

    Thank You in advance,

    Luis
     
  2. breplum

    breplum Member

    Joined:
    Oct 2, 2004
    Occupation:
    Plumbing and heating contractor
    Location:
    San Francisco Bay Area
    The Copper Development Association had a recommendation of 5 ft. per second for hot water.
    The Navien recirc pump should be fine for most any loops within the range that they recommend for the internal pump.
    The Navien dedicated loop maximum includes supply and return as the total allowable (including fittings) 100' for 1/2" copper and 500' for 3/4" copper.
    Head is what affects the GPM as well as diameter, but in your case I wouldn't worry at all.
     
    Monguila, fitter30 and Sylvan like this.
  3. Sponsor

    Sponsor Paid Advertisement

     
    Monguila, fitter30 and Sylvan like this.
  4. Monguila

    Monguila New Member

    Joined:
    Feb 4, 2021
    Location:
    Vista, CA
    Thank you very much!
     
  5. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Joined:
    Sep 2, 2004
    Occupation:
    Retired Systems engineer for defense industry.
    Location:
    New England
    You generally don't need anywhere near that volume, and could probably use a smaller pump, that could save some on electricity. A smaller pump may take a bit longer to get the line up to temp, but once it's there, less only needs to overcome the radiation losses which, hopefully is small if you've insulated the lines. The pump on mine is all of 13W, and a HP is 746W if I remember correctly. WIth a tankless system, you need enough volume to turn the system on, and that small of a pump like in mine probably would not do it.

    As long as your velocity doesn't exceed the Copper Institute's recommendations, you shouldn't erode your pipes and the noise level should be minimal, if you can hear it at all flowing. On a 3/4" line, 8gpm equates to about that 5fps water velocity, but it's only 4gpm in a 1/2" line.
     
    Monguila likes this.
  6. Reach4

    Reach4 Well-Known Member

    Joined:
    Sep 25, 2013
    Location:
    IL
    There are different ways to do hot water recirculation. A system that runs continually or for long periods should have a low flow rate.

    Systems where the recirc only starts after you push a button should be higher flow rate to minimize the wait. Those are most energy efficient, but not instant-- you need to push a button and wait for some number of seconds. Each method conserves water.

    A 1/2 inch pipe is better to the lavatory hot, and 3/8 is better still if you are going to wait for the hot to arrive. You cannot share a 3/8 with the tub/shower.

    The answer to your initial question is no.
     
    Monguila likes this.
Similar Threads: dedicated recirculation
Forum Title Date
Tankless Water Heater Forum Mini storage tank for dedicated recirculation loop Jan 3, 2012
Tankless Water Heater Forum Navien - no dedicated return loop Nov 12, 2015
Tankless Water Heater Forum Dedicated Tankless for Commercial D/W Apr 4, 2014
Tankless Water Heater Forum Rinnai RUR199I Recirculation Pump Noise Apr 7, 2021
Tankless Water Heater Forum Navien Recirculation Motion Sensor Jan 30, 2021

Share This Page