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Choosing a correct natural gas water boiler

I am replacing the my current 150K BTU Utica boiler installed in 1999. I have a finished basement, 2 main floors and an attic to heat. 2200 sqft. Heat loss calc on the Slate Fin App was 94k BTU. I like the home at 75 degrees and estimated for the coldest day of the year at 1 degree. I currently have 62 feet of baseboard (actual filament length), 28 ' of 9" high cast iron baseboard, and 2' of 18" high radiator ( 10 section/5 column). How many BTU Boiler do I replace it with? I have no background in heating and probably won't understand half the stuff you right and will not be familiar on how to provide more info to pu the puzzle together, but, if you take the time to respond, I appreciate the feedback and will try to read up on what I don't understand. I live in Staten Island, NY.


  • Jamie Hall
    Jamie Hall Member Posts: 23,428
    Well you've done the first step! Bravo! That is calculating the structure heat loss. And that gives you the boiler size you need, since you are dealing with hot water heat. So something in the 94K to 100K range would be ample.

    The amount of radiation you have will control what temperature the circulating water has to be at to provide best results.

    The next steps get a bit messy, as there are a wide variety of boilers available. Some are what are called mod/con boilers; these adjust their output water temperature to suit what is needed by the heating system and are, or can be if they are set up correctly, more efficient. Some don't do that, so are slightly less efficient -- but are cheaper to install and maintain.

    The next step, really, is to find a very competent heating contractor, unless you yourself are planning to do the work. The reason for that is the success of a new boiler is about 95% up to the skill of the installer and only 5% the boiler. There are a number of good men listed here on the Wall ("Find a Contractor tab") who work in your area.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Ironman
    Ironman Member Posts: 7,379
    You need to check the data on your heat loss calc. You're at almost 43 btus per square foot. I've been doing load calcs for 40 years and I've never seen a house require more than 32 btus per square foot - even old leaky farm houses.

    I second what Jamie said about finding a good hydronic contractor. He'll make or break the job.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • KC_Jones
    KC_Jones Member Posts: 5,741
    Also a quick napkin calculation tells me you have ~60k BTU worth of emitter so you shouldn't need a boiler any larger than that.

    I think you definitely need to revisit the heat loss calculations.
    2014 Weil Mclain EG-40
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