Finding the Right Re-Circ Pump

Discussion in 'Tankless Water Heater Forum' started by rustlerski, May 2, 2013.

  1. rustlerski

    rustlerski New Member

    Messages:
    2
    Location:
    SoCal
    Hello,

    I recently replaced our old 40 gallon water heater with a new Takagi T-D2U tankless. The unit is mounted on an exterior wall. One of the expected results of this is that there is now a long wait for hot water in our bathrooms. The old system had a re-circ loop that is capped off for the time being. Direct line it is about 50 ft. from the new tankless to the farthest bathroom. I do not know the overall pipe run length under the house.

    I'd like to install a new re-circ pump that is compatible with the Takagi. Models with a timer/aquastat are preferable to push button. According to Takagi, "the only requirements we have are that it needs to be able to push minimum 2gpm, maximum 4gpm through the system with 1/12hp."

    I'm having a hard time finding the right model that seems to fit within the requirements.
    Any recommendations on a pump that fits these specs?
    Are there any that can be mounted outside next to the Tagaki? If not, I suppose I could put the pump in the laundry room right where the old re-circ loop is capped at the moment (about 20 ft from the tankless).
    As an alternative, I know there are systems to go under the faucet at the end of the line. Any pumps that would make sense for this? I've seen some that would allow me to abandon the re-circ loop entirely, but do not know if that is a good idea.

    Thank you very much!
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,990
    Location:
    New England
    I do not know if any of the versions of the RedyTemp systems (they have a bunch of different ones now) would meet your requirements, but I do know they at least do use the controls you're interested in. They can use the cold water as the return line, or preferably, when you have one, a dedicated return line. I have one installed under my vanity that's been working now for nearly a decade.
  3. lifespeed

    lifespeed Member

    Messages:
    321
    Location:
    California
    I have had good results with the Redytemp and Noritz tankless. You definitely want to use a dedicated recirculation pipe.
  4. rustlerski

    rustlerski New Member

    Messages:
    2
    Location:
    SoCal
    Thanks for the lead on the Redytemp systems. I had not come across those.
    According to Redytemp, the best model for my house would be the TL4000D , however this is only 1/25 hp and does not meet what Takagi told me was needed. As the TL5000D is 1/8 hp, am I better with this one and just limiting the flow range manually by adjusting the valve openings (which it says can be done)?

    I'll plan on keeping the return line, too.

    Any other thoughts?

    Thanks!
  5. lifespeed

    lifespeed Member

    Messages:
    321
    Location:
    California
    I'm sure you'll enjoy the convenience of the re-circ pump. It is some extra work, but at least you already have the dedicated line. I assume the return is 1/2", while possibly the hot water supply to the furthest sink has sections of 3/4" or larger?

    The install I did is 60' to the furthest sink where the return is plumbed in 1/2", hot water to the sink fed by 20' of 1" and 40' of 3/4" and is pumped by the Redytemp TL4000. I just recirc the furthest (kitchen) sink. The bathrooms only have 4' and 10' of uncirculated piping, so I did not recirc these.

    If I had it to do over I would probably use the TL5000D and plumb the recirc pipe 3/4" to drop the dead cold pipe flush time from 90 seconds to an estimated 30 - 45 seconds. But it is done now and not worth revisiting. Besides, with the timer function providing hot water in the morning and evening automatically, and the momentary Leviton Decora rocker switches to activate from each of the three locations, it is still pretty convenient.

    I do intend to do one last wiring upgrade, where I will connect a relay between the tankless heater and the recirc pump, causing the recirc pump to turn on if the tankless fires up and the pipe is still cold. This way, if anybody uses hot water, even briefly, the heater will continue to fire until the long pipe run is heated. If the heater is going to fire up, may as well ensure, automatically, that it heats all the pipe even if the user didn't push the button, and it is during "off hours" when the timer doesn't call for recirc.

    In your case I would determine if the 1/8HP pump will play nice with your 1/2" dedicated return. Assuming water velocity will not be too high, I would run the big pump. I suspect you will not need to valve-restrict the return unless you need to balance multiple return pipes. You don't state your heater's max GPM at your coldest feedwater temps, but would not want the pump to outstrip this capacity limit.
  6. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,990
    Location:
    New England
    With a tankless, the flow rate must be high enough to trigger the system to turn on, so the tankless company figures you'll need a certain sized pump. You'd have to run the numbers to verify the sizing, but I'd guess they know what they're talking about.
  7. pkboulos

    pkboulos New Member

    Messages:
    3
    Location:
    New York
    Navien 180 ASME GAS COMBO Boiler/Hotwater heater / Carriage house?

    All,

    i am renovating a lofted one bedroom space maybe 600 sq feet above 2nd floor of a carriage house. i want to purchase this unit but i am worried it may be "too big" for the space?

    i would use it for baseboard heat and hot water... would there be any downside if it was too big? it says min output BTU of 17,000k... I dont have a lot of knowledge about this and need some help.

    I need to use gas as a i dont have enough electric for baseboard heating, i like the idea of on demand because i dont know how often i will actually be using the space of it i may rent it or what.

    thank you
    Peter
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