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Help with Boiler size-up

John B_2
John B_2 Member Posts: 46
I have about 420 feet of copper fin tube in a building. Would it be fair to multiply that by let's say 580 to come up with a new cast iron boiler size? It's a ten unit motel building that was converted into an apartment building. One floor on a slab, cinder block walls, one living room, one bedroom, and one bathroom times ten. About 475 sq feet total. Flat roof with barely any insulation. Each unit has about 38 feet of 3/4 in fin tube in all.

The existing boiler has a gas conversion burner pulling out about 340,000 btu/hr from the meter.


  • Ironman
    Ironman Member Posts: 7,225
    edited October 2010
    You Need To...

    Do a heat loss calc. and size the boiler accordingly, not according to the radiation. It may be over-sized. If it is, that's OK because the boiler water temp may be able to be lowered some in that case. That would lower fuel consumption.

    I would highly recommend that you install a good mod/con. with outdoor reset. Your fuel savings would be significant. 40% to 50% is not unusual.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • John B_2
    John B_2 Member Posts: 46
    did heat loss calc

    Thanks. I remember doing a heat loss calc last year which gave me a 240,000 heat loss (if I remember correctly). I remember having to guess at some of the insulation factors. I don't remeber it asking anything about the installed radiation. Is 240,000 what the new boiler output should be or is it the input or ibr rating? Don't think a mod/con is in my budget right now.
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