Replies

1. 
   user-2310254 | Nov 09, 2020 09:21am | #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 | Nov 09, 2020 09:50am | #2

   Hi Matt,

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

3. 
   brad_rh | Nov 09, 2020 01:51pm | #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 | Nov 12, 2020 07:52pm | #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 | Nov 12, 2020 11:06pm | #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 | Nov 13, 2020 11:23am | #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.

5. 
   wab | Nov 01, 2022 09:27pm | #7

   OK. I have another related issue on this topic that I would like to share and hear opinions. I installed a new hybrid water heater (Rheem/Rudd) in combination with a circulation system and recently had problems in heat pump mode with the heat pump running continuously and apparently getting so cold that it could no longer keep the water hot. At least that is what I was told by Rheem technical support. They indicated that the WH has a flow sensor that detects flow and that activates the heat pump and that it was not designed to be coupled with a continously running circ system for that reason. They suggested that the only fix was to put the circ system on a timer or to have a separate sensor or remote in baths to activate pump when hot water would be needed. We are in an area where water conservation is very important and so the extra water to wait for hot without the circ system results in significant water wastage. Apparently they do not have an option to detect temp threshold to activate the heat pump, only flow. We are working thru this but I thought important to point out in this thread because even if you well insulated the piping for the recirc system so you can run it continously during the daytime efficiently (with minimal heat/energy loss), the flow will activate the heat pump which will run continously and apparently result in failure to deliver hot water related to over cooling in the body of the water heater due to continous running of the heat pump. Any thoughts??

1. 
   walta100 | Nov 01, 2022 10:12pm | #8

   Sound to me like someone is trying to baffle you with bull stuff. I say call his bluff ask for the part number for the water flow sensor in the hybrid heater and have him circle it in the parts diagram. Yes, there is a flow sensor in the tankless water heater so maybe he is confused.

   When I read the patent for the Rheem controls every mode was programed to turn on the heating element if the HP failed reach the set point after some amount of time and I do not recall a flow sensor.

   If your loop did somehow manage to lose more than the 4200 BTUs per hour than the heat pump can produce then the HP will never keep up.

   If your HP did happen to have leaked some refrigerant it seems likely to have the symptoms you are describing.

   Walta

6. Expert Member
   DCcontrarian | Nov 02, 2022 09:00am | #9

   You could put a five-gallon resistance water heater downstream of the HPWH and plumb the recirc into it.