Steam boiler sizing; EDR factor for 3rd floor apartment

Discussion in 'HVAC Heating & Cooling' started by mckennatim, Mar 14, 2015.

  1. mckennatim

    mckennatim New Member

    Sep 30, 2012
    I know that typically there is a 1.33 factor figured in for piping. What would be a good factor in the case where the new boiler is serving a third floor apartment? Compared to an apartment on the first floor, there are 7, 1 or 1-1/4 ~20' each, pipes (~ 140 more feet) running through the walls of other apartments to supply the 8 third floor radiators.

    One pipe steam, EDR = 261, radiator load 62,500 BtuH

    Last edited: Mar 14, 2015
  2. Tom Sawyer

    Tom Sawyer In the Trades

    Nov 29, 2010
    You also need to know the input of the radiators, however, steam is a different animal than forced hot water. When the system was originally sized and installed the boiler was chosen to match the radiation and while I'm sure the heat loss of the home has been improved over the years through the addition of better windows, doors and insulation, the radiation and piping still need to be properly fed so to speak so when installing a new steam boiler, the best practice is to closely match the output of the existing unit because a smaller boiler will make steam faster but with less volume and what happens is the piping and radiators take the steam and the boiler water level drops either shutting off the burner ( short cycling) or if you have an automatic water feed, it feeds more water and on the off cycle e boiler over fills when the condensate all comes back.
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