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Extremely oversized boiler - what to do? cost impact?

elfie Member Posts: 266
spent some time figuring out BTU contributions from radiators by looking at sizing charts.

as it turns out, the radiators have a capacity of 750,000 btus and boiler per label on boiler says 2.9 million btu capacity

the space being heated up is one large room for 1500 and is not used on a daily basis. the building has hot water heating in other rooms so steam boiler can be turned off for several days when really cold.

current radiators are more than adequate to heat up space when temps are 5-10 degrees  (even when half the rads are turned off)

how much additional NG is likely being used in light of what appears to be extreme over capacity; its a big boiler and seems that just starting and heating it up is costly

theoretically a boiler capacity of 1 million btus would likely be adequate.  by having a higher boiler capacity it doesnt mean that space will heat up more quickly.  is this all true and what can be done to correct this situation?


  • Jamie Hall
    Jamie Hall Member Posts: 23,450
    What were they thinking?

    or did the boiler used to heat something else as well?  Assuming that you've added up the radiators and converted the EDR to BTU correctly -- and no reason why you shouldn't have -- you are way over capacity and I dare say you have some venting and possibly water hammer issues to go with it.

    However, with that much over, it's very unlikely that there's much to be done about it except changing out the boiler -- and that's going to be costly.  I honestly don't know how much loss of efficiency there is with that much over; bound to be some.  Would it be cost effective to change?  Hmm... How old is the boiler?

    If it's a young boiler in good shape, have you thought of taking some of the hot water heating load off this boiler, rather than whatever is firing the hot water?  The plumbing and controls might be a bit odd, but I should think doable...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • elfie
    elfie Member Posts: 266
    oversized boiler - no clue what they were thinking

    the facility has both a hot water and steam boiler and both are very oversized.

    no venting problems that i am aware of, but there is hammering due to mains not being able to fulling relieve condensate since the pressure is not constant due to zone valve modulation.

    the boiler is about 12 yrs old.

    there are a couple steam coil blowers (in addition to radiators - btu calc includes both blowers and rads) and since there is a 3 inch heating hot water pipe within 15 feet, there may be an opportunity to shift capacity over to the hot water boiler by converting the steam coils to hot water coils

    this may lead to a substantial reduction in how much the steam boiler is used

    is it safe to assume that a grossly oversized steam boiler is much more costly to operate? i suspect this is the case; sadly, switching over to a smaller boiler is not cost effective.
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