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Old 04-20-2015, 08:13 AM   #1
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Retrofit to create a HW recirc system


We recently moved into a 7 year old single story home. It is quite long (110') one end to the other with bedrooms at both ends. The primary water heater is in the center of the home in a closet. There is also a small water heater in the crawl space at one end of the house. The bed/bath room nearest the small water heater gets virtually instant hot water while in the remainder of the house you have to wait up to a minute or so to get hot water.

I have done my best to draw up the complete domestic water system, since it is easily accessible in the crawl space. We have our own deep well system that is supplied by a constant pressure pump.

Retrofit to create a HW recirc system-domestic-water.jpg

The dark blue lines are the cold water lines; the red lines are the hot water lines and the light blue lines are mixed hot/cold that supply the water for the toilets to avoid sweating during the humid times. The two mixing valves are shown along with a photo of the mixing valve.

My goal is to reduce the time needed to get hot water everywhere with the minimum amount of work/cost. Since there is no actual 'return' line to the water heaters, I am wondering if there is a simple way to just make a cross connection somewhere and add a circulation pump to create a hot water loop? Thanks.
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Old 04-21-2015, 08:04 AM   #2
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Since you have a crawl space. adding a recirc loop should be pretty easy.
Do you really have a 120 gal. heater? The 50 will heat enough water for a 2 bath home.
By adding the loop and pump, you should be able to remove one of the heaters.
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Old 04-21-2015, 08:43 AM   #3
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Yep, really is 2 water heaters and the big one is 120 gal. Since they are both there, I have no need to remove one, especially since the big one is heated by the 'waste heat' (essentially free) from the heat pump de-superheater.

My plan is to tap into the outlet line on the 50 gal. heater and put a recirc pump with a 1/2" line connecting near the kitchen sink and then continuing on ending at the bed/bath near the well. That should create a loop that sends hot water back to the 50 gal. unit.

I am leaning towards a Grundfos Comfort PM series since it has the 3 operating options: 1) learning 2) temp actuated or 3) 24/7.

Thanks for the input.
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Old 04-21-2015, 07:49 PM   #4
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Quote:
Originally Posted by Donl1150 View Post
Yep, really is 2 water heaters and the big one is 120 gal. Since they are both there, I have no need to remove one, especially since the big one is heated by the 'waste heat' (essentially free) from the heat pump de-superheater.

My plan is to tap into the outlet line on the 50 gal. heater and put a recirc pump with a 1/2" line connecting near the kitchen sink and then continuing on ending at the bed/bath near the well. That should create a loop that sends hot water back to the 50 gal. unit.

I am leaning towards a Grundfos Comfort PM series since it has the 3 operating options: 1) learning 2) temp actuated or 3) 24/7.

Thanks for the input.
There is something about your plan that bugs me but I don't know what it is...
I haven't piped a system with a remote tank such as yours. But recircs typically return to the cold inlet of the heater.
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Old 04-21-2015, 09:22 PM   #5
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While the system does have a 'hot' line going to the cold input of the small tank, that water in essence is certainly not 'hot' water. It basically only serves as the fill line & pressure source since hot water for the bathroom south of the laundry room has to come only from the large WH. Reason being is the outlet from the small WH only supplies the bath directly to its left. There is no way for hot water from the small tank to get to any of the other outlets in the rest of the house.

That will remain the case as well after I install the recirc loop since I will put a check valve in the new line. But, with the new recirc line, the 3/4" fill line for the small tank will now carry cool water to start and once the hot water arrives from the large tank, the circ pump will sense it and shut down.

Ordered all the parts.....hope it all works as planned. We shall soon see....
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Old 04-21-2015, 10:11 PM   #6
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IMO- the loop should be 3/4" starting at the 50 gal hot outlet. Run it to the far bathrm. and connect to the existing 3/4" hot.
At the 120 gal heater the existing hot to the near bathrm. is noe the recirc retun and would connect to the 120 cold inlet. Also the pump would be here with the appropriate check valves.
This will create a loop from the 120, through the 50 and back to the 120. The 50 becomes just a re-heater if needed.
The kitchen can be picked up on the way back.
But, like I said earlier, I haven't piped something like your layout- keep us posted
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Old 04-22-2015, 08:41 PM   #7
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Is the heat pump on the A/C's ? this system seems extremely over thought and extremely inefficient an over kill. lose the small heater run the third line if the heat pumps are for the A/C recovery you'll need to make sure that those are piped in correctly also.. thats if the drawings accurate..
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Old 04-22-2015, 09:59 PM   #8
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The home is both heated and cooled via 2 ground source heat pumps; one 4 ton the other 3 ton. In addition, there is a backup propane fired forced air furnace. The heat pumps provide the heat source for an in-floor radiant heating system and they also run to a heat exchanger in the forced air furnace in the event the radiant floor system is unable to keep up. This was our first year in the house and even when the temp went to -25 F, the radiant kept up and the heat pumps never diverted to the forced air furnace. The propane never kicked in either.

The diagram I have drawn is for the domestic water only. You will note the heat pumps are the first thing serviced by the well water. As I mentioned earlier I believe, the large WH is dual fuel as well; electric and supplemented by a line from the de-superheater off the heat pumps.

My proposed plan will not affect the heat pumps (either heating or AC) in any fashion.
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Old 04-26-2015, 05:09 AM   #9
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Quote:
Originally Posted by Donl1150 View Post
Yep, really is 2 water heaters and the big one is 120 gal. Since they are both there, I have no need to remove one, especially since the big one is heated by the 'waste heat' (essentially free) from the heat pump de-superheater.

My plan is to tap into the outlet line on the 50 gal. heater and put a recirc pump with a 1/2" line connecting near the kitchen sink and then continuing on ending at the bed/bath near the well. That should create a loop that sends hot water back to the 50 gal. unit.

I am leaning towards a Grundfos Comfort PM series since it has the 3 operating options: 1) learning 2) temp actuated or 3) 24/7.

Thanks for the input.
Well, things are installed as planned (those push on connections are amazing) and work as expected....with one exception.......getting no quick hot water at the northern most bedroom. After I let the hot water run for a bit, I checked all the lines by touch to see exactly where the hot water was going. Turns out the water was taking a 'short cut' in its return to the 50 gal WH. At the connection by the kitchen sink where the recirc line continues to the northern most bedroom, the hot water was simply headed back to the WH rather than continuing on to the bedroom before returning. I will have to install a check valve in the supply line to the kitchen hot and that will force the recirc line to work as intended, serving all areas.

I will have one happy wife now!!
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Old 05-05-2015, 06:22 AM   #10
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Installed the check valve near the kitchen and now all flows as planned. Instant hot water at all locations! And that recirc pump is whisper quiet....amazing!
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