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Posted by steve on January 08, 2008 at 14:42:20:
In Reply to: Re: boiler sizing posted by ps on January 08, 2008 at 13:31:18:
: Your EDR comes to 177,600 Btu. With 15% added for distribution losses, etc - that comes out to 204,240 Btu. The closer you can size to your load the more efficient the boiler can operate. Short cycling is bad for efficiency and the system as a whole. Make sure whomever you get is experienced with steam systems, not just any old contractor.
My understanding is you need 33% pickup on a steam system so it would be 236.2 MBtu.
Either way, it seems the most accurate way is to look at the I=B=R rating for steam BTU or steam sq. ft. The next question is how much above boiler size C do you have to be to go up to boiler size D or do you always upsize so there is adequate steam volume.
It seems odd that the old inefficient boiler could heat the house with a 245 MBtu input from oil (1.75*140,000) and a new boiler will need to be a good deal larger on the input to make sufficient steam.