Plumb two HPWH in Series or Parallel??

The Tank Plumb two HPWH in Series or Parallel??

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    Plumb two HPWH in Series or Parallel

    First, let me explain my situation. I have a 4100 Sq Ft Single Story house, with copper pipes buried in the slab. 80 gal Elec water heater with Grundfos Recirc Pump. Because of the length of the recirc system, and the heat loss in the slab, I have to keep the recirc going from 6am to 6pm every day. Otherwise, it takes 15 minutes to get hot water to the kitchen ( last stop on the HW loop). Cost for Hot water is $150/mo.

    Bought an external HPWH last year, thinking it would help , and it did. However, it can’t keep up with the heat loss,and the HW temp continues to fall during the day. By the end of the day, water is down to 90 degrees or less. It get’s cool enough during the winter that the upper element of the Electric Heater is kicking on several times/day!

    Did a lot of calculations, from several different directions, and they all came up with the BTU/hr demand of approx 10,000 BTU/hr. The HPWH has a 6200 BTU/hr capacity, so not enough.

    I’ve looked at alternatives ( point of use water heaters, solar, re-piping the house, etc) but came up with the solution to add a second HPWH. This would give me 12,000 BTU’s/Hr capacity, and should be able to keep the water hot throughout the day. I found a good deal on a second one, but wanted to discuss whether to add the HPWH in series with each other, or run them in parallel.

    Thanks for your thoughts


    Update: Talked to the HPWH company today, and they said no way to wire two of them together, without replacing the one I have now . Don’t want to do that, so pursuing other options.


    Larry Weingarten

    Hello: It’s a bit of a reaction, but I’d look a little more at repiping in an attic if you have one and eliminating the big heat loss under the slab. Re-piping gives you a system that takes far less energy to run and gives you better service essentially forever. Also, there is little to fail over time. Adding more heating capacity is something you’ll have to pay for every month. There must be some break even point in time when comparing multiple heat pumps and re-piping.

    PEX is pretty easy to run and if it’s buried in attic insulation, will deliver water at the temps you want. You might look into “structured plumbing”.

    Yours, Larry

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