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Using a Rheem water heater for hydronic and hot water

AndrewHern Member Posts: 8
Hi everyone. Do you think I can use a gas Rheem water heater for simultaneous hydronic heating and hot water? The model number is xh40t06pv40uo. According to this models use and care manual (page 31), it says that yes, you certainly could. But you have to make sure that every valve etc is suitable for use with drinking water. Also you have to set a timer and make sure the system turns on every 6 hours for 1 minute for the purpose of keeping microbes from growing. 
I live in northern New Jersey and l own a two family 2000sqft home. I was thinking of buying one water heater tank for each 1000sqft family dwelling. Any advice would be greatly appreciated. Thank you. 


  • Jamie Hall
    Jamie Hall Member Posts: 23,322
    Well, yes, technically you can, provided the water heater has the power to heat the house. Do I recommend it? No, I don't. A water heater -- particularly a tank type -- is intended to heat and store hot water, providing it for occasional relatively high flow but relatively short duration domestic use. A boiler, such as might be used to heat a house, is intended for a lower flow, usually, of hot water -- continuously. Very different demands.

    And I do NOT recommend mixing your heating water and your domestic drinking water. Ever.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • AndrewHern
    AndrewHern Member Posts: 8
    Thank you Jamie for your comment. I really appreciate it. Wouldn’t having a timer run the system every six hours for 1 minute Eliminate the microbes in the system? 
  • hot_rod
    hot_rod Member Posts: 22,157
    Legally yes, if the manufacturer has it listed. In addition to Jamies comments, they are not very efficient, maybe high 70%.

    2000 su feet could require as little as 20,000 btu/ hr, maybe as high as 60,000. So a heat load would be needed to see if it even has the btu needed to cover the loads
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • jumper
    jumper Member Posts: 2,259
    Copper is not supposed to scale but....
  • Jon_blaney
    Jon_blaney Member Posts: 316
    I have been doing it for 20 years, no problem. I use a hydroair system on an oil fired tank. I do not think you can find radiators or baseboard that is compatable with DHW. You would need a heat exchanger. System becomes more complicated. Check the First Company and Bock website for info. Run the take at 140 deg to kill the bugs.
  • Alan (California Radiant) Forbes
    This company has a lot of good options for heating with water heaters:

    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • rumble55
    rumble55 Member Posts: 2
    edited January 22
    Rheem sells a hydronic air handler made to work with their tankless heaters. Automatically does the recirculation of the water pump timing. My last tankless unit was 85% ran for 11 years, just changed to new 95% unit. My 1500 sq ft ranch w 2 baths runs great on 200000 BTU system. Northeast so we get cold weather.
  • mattmia2
    mattmia2 Member Posts: 9,662
    No. Technically you can but it will work much better to buy a boiler and also make DHW with it.
  • Teemok
    Teemok Member, Email Confirmation Posts: 491
    Don't do it. The approvals Rheem got for this type of arrangement is mostly for small condos with tiny hydronic forced air coil heating loads and one bath.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,844
    edited January 23
    What is heating the 2000 sq ft building now?

    If you have iron pipes or cast radiators then the water heater idea is a no go. You need all components to be compatible with Potable Water. Cast iron pumps , radiators, and other components will rust and scale in the “open system environment” of a water heater. And you will not want to take a shower in that water either.

    That said there are water heaters that have heat exchangers inside them that separate the potable water from the CH (Central Heating) system. They will require a separate expansion than and relief valve because that is a closed system that has no connection to the potable water relief valve in the water heater. I have explained this in detail in this comment. https://forum.heatinghelp.com/discussion/comment/1785610#Comment_1785610

    This is the model number of a Bradford White water heater with the heat exchanger inside the tank CDW2TW50T10FBN. I'm sire there are others. I see the benefit of this application because of limited space for a boiler and a separate water heater. However if you have the room I would go in the separate heat and hot water option. Easier to replace in the future when something fails.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics