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Re: boiler sizing

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Posted by ps on January 08, 2008 at 13:31:18:

In Reply to: boiler sizing posted by steve on January 07, 2008 at 20:05:53:

: Whoops. Posted first in the commercial forum.

: I currently have a very old oil boiler (converted from coal). It ran a 2.25 nozzle and was downsized to a 1.75 nozzle. I calculated the EDR to be about 740. Plumbers are quoting a 315,000, 298,000, and 175,000 BTU boilers.

: The small size plumbers says the big ones will short cycle and the new one is more efficient so it doesn't need to be as big.

: The large quotes say the big one will run less and cost less to operate.

: The house is stucco, storm windows, 3100 sq ft and a basement near the shore so there can be a stiff breeze in winter. How does one resolve the size difference? My GC will do whatever I want. I want the appropriately sized system that is as efficient as steam can be.

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.

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