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sizing a boiler

Hollis Member Posts: 105
OK, I see the posts of sizing by radiation but we have a big brick apt house that we obtained and the boiler that was there was heating this building which had a lot of air infiltration, little insulation in the ceiling, none in the walls and 54 single pane windows. Now we have done serious air sealing, R 60 in the ceilings, double pane low E windows etc..

Based on that do you still try to size the boiler on the same radiation?


  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,576
    steam sizing

    yes, still size the boiler to the radiation, and as a result of all your insulation it will run less, if:

    1. if changing the boiler, do not go by the rating of the old boiler, but instead, add up the ratings of all the radiators, and size it from that total, and pipe it right.

    2. you put on plenty of main vents , to let the air out for the steam to get into the radiators.

    3. you keep the pressure down.-[2-8 ounces are recommended]

    4.put the thermostat in the right location, and set it right for steam, or choose another type of control, such as the tekmar279.--nbc
  • BobC
    BobC Member Posts: 5,478

    You will have to make a chart that lists the square footage of all the radiators in the place. With any luck most of the apartments are very similar in the number and types of radiators that they contain. Don't forget to add radiators in any common areas; hallways, lobbies,etc.

    When you add up those numbers that will give you the total number of sq ft; you then want a boiler that can feed that number of sq ft.

    Use the chart I've enclosed to figure out the sq footage of each radiator.

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • A different view of boiler sizing......


    These concepts are especially applicable if you have two pipe steam....I can send you more information on two pipe steam if you are interested.
    The Steam Whisperer (Formerly Boilerpro)

    Chicago's Steam Heating Expert

    Noisy Radiators are a Cry for Help
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