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Does baseboard loop from condensate return add to boiler BTU

Joseph_4 Member Posts: 274
I have a customer who has a two hundred thousand BTU boiler.They have about 50 to 70 thousand that they need for two baseboard loops I want to add an everhot tankless unit to accomplish this. Does it subtract from the boilers BTUs thanks Joseph HHI services


  • Jamie Hall
    Jamie Hall Member Posts: 23,433
    This is steam, I presume? What is the EDR load of the system without the baseboard units? What is the EDR rating of the boiler (sorry, but "two hundred thousand BTU boiler" just isn't useful information -- is that gross input? Net output?).

    If the EDR load of the system and the EDR rating of the boiler are similar, or if the boiler is oversized, then you should have no problem with the baseboard loops. They don't feed off the condensate line, though -- they come off the boiler itself below the water line. They can return to the condensate line.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    EBEBRATT-Ed Member Posts: 15,616

    But the hot water load should not exceed the piping & pickup load for the boiler which is 33% of the boiler output
  • Joseph_4
    Joseph_4 Member Posts: 274
    Ed Im curious to understand is this special specifically to steam or would it be true by forced hot water if I'm using a 15 percent pickup factor also if they removed some of the steam radiators so that this boiler is oversized then I'm assuming I would have even more BTU available for hot water loop is that correct 
    EBEBRATT-Ed Member Posts: 15,616
    edited October 2021
    This only applies to steam,

    Lets say a steam boiler has a net rating of 833 EDR/sq ft of steam radiation or about 200,000 BTUs
    which is 833 x 240 btus/square foot 833 x 240=199,920

    200,000 x 1.33 piping and pickup=266,000 so that leaves you 66,000 you can use for the hot water load maximum

    Assuming the boiler is 80% efficient (266,000 /.80)=332,500 would be the boiler input.

    Their are some other losses like heat lost through the jackett but the above is pretty close

    So in the above example, 332,500 is input, 266,000 is gross output, 66,000 is the pick up load used to preheat piping and 200,000 would be the amount of radiation that can be connected

    So a steam boiler is "oversized" by the PU factor of 1.33. The .33 can be used for a HW loop but if you use more than that the boiler may not be able to heat the connected load.