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  1. #1
    Join Date
    Aug 2007
    Location
    Sudbury, Ontario, Canada
    Posts
    20

    Combi dhw heater or combi space heating boiler ?

    What are the factors that must be considered when trying to decide on which technology to use ?

  2. #2
    Join Date
    Jul 2000
    Location
    Northern Wisconsin
    Posts
    2,037
    The main difference is how they were designed and rated. They both do both.

    The deciding factor should be how you plan on using the unit and what features are most important. Then the final thing to consider is which unit fits your needs without compromises. <See my tag line below>
    Use the biggest hammer you like, pounding a square peg into a round hole does not equal a proper fit.

  3. #3
    Join Date
    May 2008
    Location
    Missouri
    Posts
    3,615
    What do you want to do with the unit? We've installed combo units that will do both, but is that what you want?

  4. #4
    Join Date
    Aug 2007
    Location
    Sudbury, Ontario, Canada
    Posts
    20
    Well I have a 1 1/2 storey heated with a medium efficiency 125,000 BTUH input gas boiler, and a separate medium efficiency gas water heater. The house is heated with cast iron radiators fed with large gravity feed pipes. Only two people living in house with one bathtub. Would like to migrate to a single source high efficiency mod/con heating plant.

    Originally thinking mod/con boiler with instant DHW was way to go, but then started reading about possibility of a potable mod/con water heater for space heating. Seems that the potable water heater would be slightly more expensive to operate due to larger volume of water being maintained hot in the hot water heater. What other issues are there to consider ?

  5. #5
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,594
    That 125K is likely oversized, water heating needs don't add that much. So 660K used boiler can heat about 5 houses on your street!

    There are mod-cons that will do both, house heating and domestic though domestic capacity can be pretty minimal. Some of the hot water gurus will be by eventually with some suggestions.

  6. #6
    Join Date
    May 2012
    Location
    Upper Michigan
    Posts
    3,589
    Triangle tube makes a excellence series boiler that would do both for you. Look that up.

  7. #7
    Join Date
    May 2012
    Location
    Upper Michigan
    Posts
    3,589
    Quote Originally Posted by BaldLoonie View Post
    That 125K is likely oversized, water heating needs don't add that much. So 660K used boiler can heat about 5 houses on your street!

    There are mod-cons that will do both, house heating and domestic though domestic capacity can be pretty minimal. Some of the hot water gurus will be by eventually with some suggestions.
    I think you have addressed a couple threads with that reply lol.

  8. #8
    Join Date
    Jun 2010
    Location
    Philadelphia PA
    Posts
    2,198
    Of course the combi units will modulate (turn down) so the oversize problem is minimized AND the con boiler just loves those big rads with no chance of the problem of low return temps SO twith outdoor reset you may have a really sound approach under consideration
    You have got to learn from other people's mistakes! Because God knows you don't live long enough to make them all yourself !!!!!!!!

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