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Boiler heat to boiler room - 80% vs. 95%

Chuck_17Chuck_17 Member Posts: 123
Is there any data about the relative heat loss for boilers to boiler rooms?
Say around 100MBH. A atmospheric vent hot water boiler vs. a high efficiency direct vent.
The boiler and the b-vent vent/chimney being replaced with the high efficiency boiler. (assume piping is the same)

Really just need an idea (but real data is always nice).
The situation is a small boiler room on a corner of a building (two outside walls) with a door to the outside.
Will there be enough heat in the room when the boiler is replaced?


  • STEVEusaPASTEVEusaPA Member Posts: 4,113
    More important is whether there is enough combustion air if it's not being piped in, directly to the boiler.
    Is there large supply/return pipes that are uninsulated? If so, than maybe so. If not, maybe some fin tube off of the supply, or on the return.
    Is the goal heating the room or just not letting it freeze?
    Keep in mind if the boiler is sized right, it should be running almost constantly, especially when it's closer to design temperature.
  • Jamie HallJamie Hall Member Posts: 12,720
    Most of that "lost" energy is in the higher temperature flue gas. Relatively little is in jacket losses. I can't give you an exact number, and it will vary for every make and model, but the jacket losses probably won't be much more than 60 to 70 BTUh per square foot of surface area of the jacket.

    This won't change appreciably with the efficiency of the boiler, for a modern design. The differences there are in the temperature of the flue gas.
    Br. Jamie, osb

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • ZmanZman Member Posts: 5,753
    As long as the boiler is sealed combustion pulling air from the outside and you are not trying to heat the CA you should be fine. The jacket and pipe loss in most boiler rooms exceed the heat loss of the space.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • EBEBRATT-EdEBEBRATT-Ed Member Posts: 6,947
    And it depends on the water temp you are running.
  • Robert O'BrienRobert O'Brien Member Posts: 3,188
    The vastly reduced volume of water will substantially lower standby losses. The room will be noticeably cooler
    To learn more about this professional, click here to visit their ad in Find A Contractor.
    rick in Alaska
  • Chuck_17Chuck_17 Member Posts: 123
    Thanks for the replies.
    Replacing atmospheric draft boiler with maybe 6' of b-vent straight up
    high efficiency boiler, direct vent with probably the minimum length PVC vents.

  • HVACNUTHVACNUT Member Posts: 3,280
    So you're actually replacing that ☝️ boiler?
    I'm curious why of all the questions to pick from, why that?
    The only concerns are freezing and combustion air. And freezing only with a broken boiler or a nasty draft on piping.

    Did you get real data? Like a heat loss calculation, pump sizing, options for venting to code (see PVC), etc?

    My calculation says that boiler room will maintain between 52° and 74° averaging DDT and a 70° WWSD.
    Easy peasy.

    Just make sure the important stuff is figured out.
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