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GPH, run times and BTU / optimal configuration

john_230 Member Posts: 11
I can install either a 3 section or a 4 section cast iron boiler. Both can comfortably service the house which has a 102,000 design day heat loss + indirect water.

The 3 section yields 112 btu, net - and 1.10 GPH.

The 4 section can be set anywhere from 101 btu (0.95 GPH) to 155 btu (1.5 GPH).

If I set the 4 section to the 112 btu of the 3 section, will it have the same GPH and run times to heat the house to design day ?? .

Hence, will it cost precisely the same to operate.


  • scrook_2
    scrook_2 Member Posts: 610
    3 vs 4 section at same GPH

    Yes. The 4 section at 1.1 GPH input will have virtually the same net (I=B=R) output as the 3 section.

    BTW, is the calculated structure heat loss 102,000 BTU/hr?


    is the 170 linear ft of baseboard (from another post) capable of 102,000 BTU/hr (180°F AVERAGE water temperature in each zone) in which case the structure's actual heat loss is likely less than 102,000 BTU/hr, maybe a fair amount less?

    How was the performance of the old boiler at/near design day conditions and how was domestic hot water supply?
  • john_230
    john_230 Member Posts: 11
    GHP, optimal configuration, system selection


    To your question, i took a tape measure to the base board (170 feet), then took 170 x 600 btu/ft = 102,000. (is this an accurate way to estimate?)

    In addition, have 16 ft of baseboard in the basement, and also have a 40 gallon indirect.

    Independently, vendor ran his own heat loss estimate computer program and arrived at 103,000, above grade.

    We only very recently purchased, so have not much experience with water and heat hear in the winter. So far fine.

    Current boiler is steel, 112 btu, and cycles on and off periodically. house is set at 65 +/-. (3,300 sq ft)

  • Charlie from wmass
    Charlie from wmass Member Posts: 4,314

    John heat loss for hot water systems is based on building volume and design. we usually go by square footage of living space but things such as cathedral ceilings and 10 foot ceilings make me mention volume of the home. With steam we measure EDR of the heat emitters, usually radiators and piping, to find boiler size. The 4 section should be slightly higher in efficiency for the same firing rate, this needs to be confirmed by a proper analysis of the combustion gases and stack temps. The original installer may have figured 190 degree F water when they sized the baseboard so this would explain the 103K your vender came up with. ALso design temps can alter what 2 people feel is the heat load.
    Cost is what you spend , value is what you get.

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