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Boiler Sizing

Euphline
Euphline Member Posts: 1
in THE MAIN WALL
I've got a 1950's American Standard hot water system (gravity/open/130k BTU) whose time has come.



In absence of an actual heat loss calculation, I've been running some other numbers. Here's what I've got so far...



Weil-McLain Boiler Replacement Guide, 87,000 BTU.

Radiator Sq. Ft. of Radiation (480 sq. ft.), 88,800 BTU.



I've also calculated my existing usage (according to the gas company) to be about .27 therms per heating degree day. For my region, I'm working with about 52 heating degrees, so it seems to me that this, when adjusted for a (completely seat of the pants guess) 60% efficient boiler, suggests that my output needs to be about 84k BTU, which, with a 95% efficient unit, would be... 88k BTU.



Based on these three calculations, is it reasonable to conclude that no matter calculations one might dream up, anything above 90-100k BTU is oversized?

Comments

  • Tim McElwain
    Tim McElwain Member Posts: 4,633
    I would suyggest you have

    a heat loss done. Changes to the house(insulation, windows etc) may give you a lower heat loss than the original boiler setup needed.



    It was a matter of practice in the past to oversize boilers. I think you might be in the ball park with your figures but a heat loss and measure of feet of radiation will confirm what is needed.



    If you are going for Mod/Con make sure system is adjusted for your type of radiation, and that an ODR (Outdoor reset) is used.
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