Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

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

Chuck_17 Member Posts: 145
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?


  • STEVEusaPA
    STEVEusaPA Member Posts: 6,505
    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.

    There was an error rendering this rich post.

  • Jamie Hall
    Jamie Hall Member Posts: 23,447
    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
  • Zman
    Zman Member Posts: 7,573
    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-Ed Member Posts: 15,631
    And it depends on the water temp you are running.
  • Robert O'Brien
    Robert O'Brien Member Posts: 3,542
    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_17
    Chuck_17 Member Posts: 145
    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.

    HVACNUT Member Posts: 5,865
    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.