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Piping an electric water heater tank to an indirect...

Thanks Steve. The job was spec'd for a 120 gallon indirect. There are 5 full baths and 1 100+ gallon whirlpool tub. This customer is worried about gas and oil going up and thinking that the solar would be the way to go since they have a house in Florida and it seems to work great for them down there. My problem was 79 gallons is all the Viessmann solar tank holds. My rep suggested leaving the 80 gallon electric and tying it in with the indirect to have about 160 gallons of storage. Heating both from the indirect coils.

I drew out what you suggested and it seems as though I would just be making a loop from tee to tee when there is no draw on the hot water. I was thinking of tying the hot outlet of my storage tank to the cold inlet of the indirect with a check valve above the tee.But I am not sure that would work when there is a draw of hot water. Do you think I need to put a tee and tie my hot outlet of the stoage tank to both the hot and cold of the indirect? and place a valve between the tees on my hot water side of the indirect?
I was throwing all sorts of combinations around and couldn't find any I felt comfortable with. I was hoping I would find someone on here who had a similar situation, so I wouldn't have to do the installation twice.


  • Vinnie Smedick_2
    Vinnie Smedick_2 Member Posts: 17

    Could someone email me a piping schematic?
    I am installing a 79 gallon Viessmann Vitocell 300 B water heater which has two coils in it. One for solar and one for the boiler. My job calls for 120 gallons of storage due to a whirlpool bath. On the site is an 80 gallon electric water heater, I would like to use the tank as storage. Could someone email me a piping diagram for the potable water system?
  • Steve M_2
    Steve M_2 Member Posts: 121
    Is it needed?

    Vinnie, have you done the math and actually know the Vitocell 300 with the 2 coils won't heat the Whilpool? I know sometimes they spec storage demands on new construction jobs but if you show them the math, usually that'll work. Even figure using a mixing valve, which you should use anyway with solar to increase your usuable capacity.

    If you did want to use the electric water heater I would let the boiler heat it. I would install a tee out of the hot potable side of the Vitocell with a bronze IFC circulator and pump it to the hot water heater's cold inlet. You could use the lower electric water heaters thermostat to power on the circulator when the electric tanks temps drops. Then tee the hot outlet of the elect. tank back in above the other tee. I'd probably put the cirulator on a timer as well so you won't heat the electric tank when there's a demand for the whilpool or you'll never meet the demand. Sounds like a lot of extra work to me. If you're not paying the elecric bill, go ahead and hook up the 240v and just pipe it in series.
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