I'm very familiar with using a preheat or conditioning tank for domestic heat water as my prior house I did a ground loop install with a 50 gallon unpowered DSH tank followed by a final NG hot water tank. My new house was bought as prior construction (2005). It has 2 ProMax (midrange) electric 80 gallon water heaters with insulated hot water loops and circulation pumps. So it struck me as odd how quickly we ran out of hot water with showers given we have 160 gallons waiting ready to go. Well, go figure that the plumber who set the system up wasn't very smart. 1 water heater supplies the master bath, the jack n jjill bathroom that services 2 bedrooms, and a 3rd bathroom upstairs attached to a bedroom AND the pool area bathroom and shower. The second tank? Supplies a rarely used guest bathroom ONLY!?! What the heck? So clearly the system needs a little work. My thought is to plumb the tanks in series vs parallel so I have a pre-heat and a final/conditioning tank setup. To add efficiency and to greatly increase 1st hour hot water delivery I was thinking we could remove one of the tanks and put in it's place an 80 gallon heat pump water heater that would run in heat pump only mode for all but the coldest months (mild climate in Washington state (98942) with average winter temps 30s, summer temps 90s-100. Water heaters are in large 3 car garage, lots of room, lots of power. So I would envision cold water, heat pump water heater set to 110-120dF. That output going into the existing 80 gallon electric water heater, then that supplying the entire home. The circulator pumps are already on a timer so they are only on during periods of high shower/water demand (4 hours or so a day) I was thinking I would just have the circulation loop be supplied only from the electric finishing tank (so dedicated return and supply for circulator pump was only from finishing tank. Thoughts on this plan?

If the circulator return temp is typically less than your heat pump water heater temp, then run it back to there and let the HPWH do some of the work of warming it back up.

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I would definately plumb them in series what kind of tank you use is up to you from there but I agree with jon that there is no sense cutting the HPWH out of the loop if you buy one.

Look real hard at putting the recirc pump on a demand basis only. Configure a 5 minute pushbutton to run it only when you are about to bathe.

Posted By engineer on 15 Nov 2014 09:32 PM
Look real hard at putting the recirc pump on a demand basis only. Configure a 5 minute pushbutton to run it only when you are about to bathe.

That seem like a good idea...Setting up a low voltage push button at the point of use can be done with: SQUARE D TIME DELAY RELAY 120 VAC 0.1-10 MINUTES MODEL 9050JCK16V20