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Help! Can I use a single water heater for two purposes?

AndrewHern Member Posts: 8
Hi everyone, I’m new to the board. Can I use a single tank water heater for both purposes of heating my home and hot water? Is it legal? Is it safe? I live in northern NJ. 

Thank you,


  • Larry Weingarten
    Larry Weingarten Member Posts: 3,388
    Hi and yes it can be done as long as you keep the potable water separate from the heating water by using a heat exchanger. Also, if the heating load taxes the water heater too much, it can greatly shorten the heater's life, as they aren't made to fire continuously.

    Yours, Larry
  • hot_rod
    hot_rod Member Posts: 22,472
    As per the 2021 IPC you can use a listed tank to do combined systems. Apollo and a few others are listed.

    Most plumbers shy away from mixing potable and heating water. Health and liability reasons.

    There are some aftermarket plate HX modules for separating.
    At some point a separate stand alone heater may be less $$.

    There are some tank type water heaters listed for hydronic applications, stand alone.

    The CombiCors are an option, special order and them price is getting close to a combi boiler.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Mad Dog_2
    Mad Dog_2 Member Posts: 7,241
    I have a picture of a nice Combi-Cor I did with ALOT OF radiant connected to it.  It was a 50 gallon Model and heated 1/2 the house...Very happy w those Brad White Combis Mad Dog  🐕 
  • JohnNY
    JohnNY Member Posts: 3,244
    Legal in NJ, not in NYC.
    Contact John "JohnNY" Cataneo, NYC Master Plumber, Lic 1784
    Consulting & Troubleshooting
    Heating in NYC or NJ.
  • jumper
    jumper Member Posts: 2,331
    In the seventies Apollo & others advertised circulating DHW through air handler for heating. Tank heater was more efficient than furnaces or duct heaters in those days. For low heating delivery and high DHW demand like ski chalet idea wasn't as dumb as it sounds. Plus coil could be used for wimpy A/C.
  • Jon_blaney
    Jon_blaney Member Posts: 322
    I use a 32 gal oil fired Bock water heater for hydro-air and heat half of my house. System has been in place for 20 years, no problem. I do not have a heat exchanger. This is a high fire tank, 104000 btus, I think.
  • Mad Dog_2
    Mad Dog_2 Member Posts: 7,241
    Yes, legal in every municipality in NYS.  Otherwise.  Mad Dog
  • ethicalpaul
    ethicalpaul Member Posts: 5,792
    Everything's legal in NJ!

    NJ Steam Homeowner.
    Free NJ and remote steam advice: https://heatinghelp.com/find-a-contractor/detail/new-jersey-steam-help/
    See my sight glass boiler videos: https://bit.ly/3sZW1el

    Mad Dog_2
  • Mad Dog_2
    Mad Dog_2 Member Posts: 7,241
    Gotta Love Joisey...."You from Joisey???
    I'M from Joiesey!!!"  Second best place to live & work.  NY, the cool Older brother is the Best!   Ha ha   Mad Dog