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Boiler sizing

johny Member Posts: 19
Theoretical Question.Have 2 level house with aheat loss of 100k btus.Have oil fired hot water boiler with net output of 100k btu.Have 140k btus of EDR.Boiler heats house fine but never comes up to temp. before tstat is satisfied.Supplytemp of 130 degrees is enough to satisfy tstat.However this return temp of 100-110 is way to low.Question:When replacing this boiler do you size it to heatloss of house or heat output of radiators.And what about the size of the circulator.Do you size for 1gpm per 10k output of boiler.Thanks.


  • Mark J Strawcutter
    Mark J Strawcutter Member Posts: 625
    size boiler to heatloss

    of house. Are you seeing evidence of condensation damage or thermal shock?

    There are many of us out there with converted gravity systems with cast iron rads that are over-radiated (and usually over-boilered, too). Our systems have been running for 25+ years with return temps under 140F and no sign of condensation damage. Not sure why - perhaps the older boilers could just deal with it better?

    If you're intent on replacing your boiler, consider modulating and/or condensing units like the Monitor MZ, Vitodens 200, or Munchkin.


  • Gary Fereday
    Gary Fereday Member Posts: 427

    That whole System is in desperate need of a "Heat loss calculation",get the free slantfin off the wall here and start there. bigugh
  • Kent
    Kent Member Posts: 18

This discussion has been closed.