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Posted by Joye Chizek on February 11, 2002 at 22:35:58:
In Reply to: Re: Anyone else concerned posted by Steve on January 29, 2002 at 05:30:24:
5 square foot is a "standard" based on gas and automatic firing being "twice as good" as coal fired boilers that were rated 10 square foot to cover all the variable in fuel and firing techniques. Go to Tech Topics on heatinghelp.com to read the story of why steam boilers have gotten so big and you'll see 5 square foot is the product of lots of people adding a bit of heating surface here and there just to be sure. The real test of a boiler is the stress temp of the metal, which is around 750 F for most kinds used in boiler manufacturing today. If the boiler is designed to operate at a max temp. of 475 F and does it with 3.5 sq. ft. of heating surface per BHP, then it is not being stressed and is therefore safe. New designs, metals and assembly techniques make a responsible less than 5 square ft. boiler possible just as automatic firing equipment and the switch from coal to oil to gas caused boiler manufacturers to agree to change their standard from 10 square foot to five square foot in the 1950's.