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Sizing of new radiation

radmix Member Posts: 194
I have a project that has an existing boiler that's connected to a system that was a steam system converted to hot water. Were building a new addition and adding panel radiators. I know how to size each existing radiator to find the heat output but the old steam piping in the basement is 2 1/2" with very long runs. This must have an impact on the heat load of the boiler. Any thoughts.


  • j a_2
    j a_2 Member Posts: 1,801
    Not really enough info,for a true answer…But flow rates and circ. sizing are important…If your adding a zone or two be careful on supply and return temps, a boiler bypass may be in order..If the owner allows post a pic or two with your thinking...
  • radmix
    radmix Member Posts: 194
    What Im asking is with the amount of old steam piping in the basement about 80' of 2 1/2", must have an effect on the BTU loss in the system as a whole. I dont think you would just count the radiator BTUs alone.
  • Fred
    Fred Member Posts: 8,541
    A 2.5" steam pipe, uninsulated has the following heat loss:
    @100 degrees = 39 BTUH/per foot
    @120 degrees = 70 BTUH/per Foot
    @ 150 degrees = 123 BTUH/per foot
    @ 180 degrees = 184 BTUH/per foot
    @ 210 degrees = 252 BTUH/per foot
    @ 240 degrees = 327 BTUH/per foot

    @radmix , Is this the info you are looking for? These numbers are for uninsulated pipes and based on surrounding air @ 70 degrees. I don't have numbers for insulated pipe.
  • radmix
    radmix Member Posts: 194
    This is exactly what i'm looking for.

    Thank You
  • j a_2
    j a_2 Member Posts: 1,801
    Great...the info passed on here by the regulars like Fred is awesome
  • 4Johnpipe
    4Johnpipe Member Posts: 479
    edited April 2015
    If you perform a room by room heat loss and are using panel radiators for the new section. You may find that you will be able to lower your supply water temperatures greatly. When designing this by mindful of boiler protection in the form of a buffer tank or a I series mixing valve to prevent the old boiler from condensing. A little prep work now will make it less painful when the old boiler needs to go...
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