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Community and Q&A

Heat pump water heater and recirculation pump

fourforhome | Posted in General Questions on

I have searched in vain for a Q/A or blog post regarding a hw recirc system and a HPWH. I thought the conclusion was that the HPWH took a big hit on efficiency because of the continual recharging of the water.

What are the pros and cons of this system?


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  1. Expert Member
    Akos | | #1

    Continuous hot water recirc adds a lot of standby looses to any type of water heater, no matter how the water heater operates. The key to it is getting proper controls.

    There are now a several controllers that look at usage patterns of the house and only run the recirc pump as needed. You can also use timer switches or motion sensors in bathrooms to trigger the recirc pump as needed.

    With this type of system, the energy penalty is a lot less while still getting the water savings of instant hot water.

  2. brad_rh | | #2

    You can also set it up with a thermal sensor in the recirc pipe and a button in the bathrooms. Push the button and the pump runs until the hot water hits the sensor. Make sure you size the pump large enuf so the hot water gets there in a reasonable time. I have a long run from the WH to the bath, so I had to get a relatively large pump ( taco genie 0011) to get the hot water there in 30 sec.
    In hindsight a configurable timer (still using the on button), would have been better. Sometimes the water in the pipes is lukewarm and shuts off the pump too soon.
    I'm sure Martin has an article on this.

  3. Expert Member
    NICK KEENAN | | #3

    I have an idea for an improvement, which admittedly I haven't implemented but I thought I'd throw out there. Rather than a button, it would be more convenient to have a system that automatically sensed demand for hot water. When hot water is being used, the intake pipe to the WH is full of cold water flowing in. When no water is being used hot water in the tank rises and the intake pipe fills with hot water. So a temperature sensor on the intake pipe could be used to trigger the recirculator.

    So the logic is: when the intake sensor goes from hot to cold, turn on the pump. Turn off the pump when the sensor at the pump goes from cold to hot.

    1. this_page_left_blank | | #4

      Maybe I'm misunderstanding, but that doesn't seem to fulfill the purpose of providing hot water on demand. In order to do that, the recirculating needs to be happening before you turn on the faucet. In your set up it seems like the recirculating starts after opening the faucet, which wouldn't provide any benefit. And it would stay on after the need for hot water has passed, which is also no benefit.

  4. Jon_R | | #5

    The below system is flow activated. But one has to decide on the goals - 2 seconds, 40 seconds, saving water?

    I have a gas water heater - so in Winter, continuous circulation would have very little net energy cost.

  5. Expert Member
    Akos | | #6

    I run a demand based recirc. Basically a flow switch connected to a one shot timer to run the pump. The timer is set so the pump can fully purge the lines.

    Although it does work, to really get it to work you need a large pump. The one I have (G&G e3-6) is too small. Hot water does get there faster, but doesn't feel instant by any means. I generally find pulsing the shower to trigger the pump and waiting a couple of seconds works much better. It might not seem like much, but it is much more annoying than my older timer based setup which had true instant hot water.

    Overall, I would stick to either a smart demand system (ie Taco Smartplus) or something motion sensor activated.

  6. tommay | | #7

    Gee, good thing you don't have to go chop some wood, get the fire going, go down to the stream and get some water, put the pot on the fire, wait until it gets hot, then wash your face.

    1. Expert Member
      Akos | | #8

      Missing the point. The whole purpose is to find to most technically complicated solution to a non problem.

      1. tommay | | #9

        LOL...or the longest answer to the simplest question.

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