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Heat Pump Water Heater in Combination with Recirculating Pump

Matt W | Posted in General Questions on

Climate zone 3, southern California.  Home is a well insulated 3600sf with 4 showers that are spread out.  Plumbing was set up to use a recirculating pump.  About to purchase a heat pump water heater until I saw this on the AO Smith literature.

“In order to optimize efficiency of this unit, it is not recommended for use with a recirculation loop. Using this in a recirculation loop may cause the unit to run excessively.”

Obviously there is an energy penalty to recirculating pumps, but redoing the plumbing isn’t an option.  Other than the penalty for the pump, is there any reason why a heat pump water heater would be any worse than a gas one in the setting of a recirc pump?

Any thoughts?

Thanks!

Matt

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Replies

  1. Steve Knapp CZ 3A Georgia | | #1

    Matt,

    You could cause the heat pump to fail prematurely. What about installing switch or sensor in each of the baths so the recirculating pump only runs when needed.

  2. GBA Editor
    Kiley Jacques | | #2

    Hi Matt,

    This question has come up before. You might find this thread useful.

  3. Brad | | #3

    There would be no difference in the energy losses compared to gas, but they must be concerned about the heat pump running a lot more due to the losses in the pipes. That's the only reason I can think of. How bad can it be though? Maybe it it doubles the run time, so it wears out twice as fast. It might be worth calling AO Smith, to see if you can get an intelligent answer. If your showers are on a regular schedule a timer on the recirc would help out a bunch. A demand (button or motion sensor) based system would even more efficient, but with a recirc system designed for continuous flow, it might take quite a while to get the hot water where you want it.

    1. ph_aficionado | | #4

      I second Brad’s suggestion. We have a Rheem HPWH and two recirculators that are timer-based. The recirculators kick in for about an hour in the morning and evening each when we know we need hot water, and are off for the rest of the day. The system works flawlessly and we haven’t noticed the water heater kick in excessively.

      We have only had this setup for about a year so can’t really comment on any effects on longevity and such aspects.

      One minor annoyance: you’ll need to reset the clock on the recirculators after every power outage.

    2. DCContrarian | | #5

      Yeah, it's not like the recirc causes the heater to short cycle or anything. Running recirc increases standby losses. That's a given. Increasing standby losses causes the water heater to run more. That's a given as well. But the additional run time from running a circulator is no different from the additional run time of simply using more hot water.

  4. Charlie Sullivan | | #6

    In addition to the other good answers here and on the linked thread, making sure your pipes are well insulated will reduced the added standby losses incurred by recirculation.

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