LOW Temp or HIGH Temp AQUASTAT for WH?

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by Handiman, Mar 27, 2010.

  1. Handiman

    Handiman New Member

    Messages:
    21
    Location:
    Nevada
    Hello, I'm trying to find out which would be the best aquastat option for my recirculating pump on my water heater (dedicated return line).

    Thermostatic Controls (2):
    The Low temp model switches the pump off at 105 degrees and back on at 85 degrees.
    The High temp model switches the pump off at 115 degrees and back on at 105 degrees.

    I can't figure out the advantages and disadvantages of each, help.

    Thanks
  2. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,615
    Location:
    Cave Creek, Arizona
    Depending on the heat loss of the piping, the water temperature in the tank, the velocity of the water in the system, and the aquastat location, the water may NEVER reach 115 degrees to turn off the high temperature model. 105 degrees at the return line is adequate for your purposes, although it could take longer to drop to 85 degrees, than it will for the rest of the system to cool down and negate the effect of the circulation system. Aquastats seem good in theory, but seldom do what you want them to do in practice, UNLESS they are installed at the end of the line near the faucet, and thus sense the temperature to the faucet, not at the heater.
  3. Handiman

    Handiman New Member

    Messages:
    21
    Location:
    Nevada
    Thanks hj. I was thinking 115 degrees was really too hot. The recirculating pump on the return line is right next to the water heater and that 1/2" copper pipe I don't think would ever reach 115.
  4. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,615
    Location:
    Cave Creek, Arizona
    as I said, however, an aquastat at that location will not respond to the actual temperature at the faucet. IF it cycles too slowly, then the water at the faucet will STILL be cool and have to flush the cooled water out before it gets hot. I have seen many aquastats which are just set as high as possible so the pump runs continuously in order to prevent that scenario. And, you have to hope the water cools down to 85 degrees so the pump even starts up again, and that will depend on the ambient air temperature in the room. The warmer the room is the slower the exposed line will cool down to room temperature or 85 degrees, whichever is higher.
    Last edited: Mar 28, 2010
  5. Handiman

    Handiman New Member

    Messages:
    21
    Location:
    Nevada
    Hey, well actually now I don't think my return line ever gets below 85 degrees. Probably b/c I always have my water heater set at 140 degrees. So now I'm thinking of getting the higher temp model 105 degrees to 115 degrees (GRUNDFOS 595656). Also, I can't seem to figure out where the aquastat ties into the pump housing, timer is already installed. Thinking I have to remove plastic pump housing (GRUNDFOS UP15-29SU/TLC) and drill a hole in it for the wiring?

    [​IMG]
    Last edited by a moderator: Mar 4, 2014
  6. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,615
    Location:
    Cave Creek, Arizona
    If the timer is integral to the pump, there is a good chance you may NOT be able to insert the aquastat between the timer and the motor wiring, since that could be a circuit board.
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