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Boiler ? Water heater?

First post (anywhere). Congrats. on your site, learning much. I would like to know, in the HVAC world, what differentiates a boiler from a hot-water heater?? The temperatures involved? the amount of hot water they can "process"?, the amount of water they keep on standby? ....... Thanks in advance. ( hey, you've got to start somewhere! )


  • meplumber
    meplumber Member Posts: 678
    edited February 2012
    The difference is usage.

    A boiler is a central heating appliance used to heat water to heat a home, business, or for industrial processes. It can heat the water to any temperature desired and to steam as well. The water inside a boiler is considered non-potable (not safe for drinking.)

    A water heater is used for heating domestic, potable water (safe for drinking). A water heater's maximum temperature is normally 150 deg F +/-.

    The most substantial difference is the water itself. But the safety and operating controls are also different. Water heaters can be indirect as well. Meaning that they receive their heat from another source (most often a boiler.)

    Water heaters should not be used as a central heating appliance. They are not approved as such and do not utilize the appropriate safety and operating controls.

    Good Question.
  • wrxz24
    wrxz24 Member Posts: 298
    high efficiency

    I know a radiant company here in Vermont who suggest using a HE water heater for their high mass radiant design.
  • boiler ? Water heater?

    Thanks for your post, it's helped clarify a few things, yet in my readings ( it may have been a Dan Holohan book ) the author talks about a contractor/installer that in fact uses almost exclusively hot water heaters for their radiant flooring jobs. ( the author did say these were High Efficiency heaters) so would that make a difference??
  • kcopp
    kcopp Member Posts: 3,990
    it may have....

    mentioned that in the book, but did not reccommend........
  • NRT_Rob
    NRT_Rob Member Posts: 1,013
    in most cases

    you can do better for efficiency with a mod/con boiler than a water heater... you can run them colder, especially on low temp heating systems.

    truly high efficiency water heaters have some advantages in that it's hard to short-cycle them, so that's nice.

    but never, ever run them in an 'Open' or "Open direct' configuration. that's a horrible idea.
    Rob Brown
    Designer for Rockport Mechanical
    in beautiful Rockport Maine.
  • Charlie from wmass
    Charlie from wmass Member Posts: 4,216
    Yes I was talking about that VT company today

    and the other installers and the instructor at the continuing education class spend their time removing those systems and bringing them to the code requirements too. Not all information on the internet is good information.
    Cost is what you spend , value is what you get.

    cell # 413-841-6726
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