Rule for Estimating Horse Power of Horizontal Tubular Steam Boilers.
Find the square feet of heating surface in the shell, heads and tubes, and divide by 15 for the nominal horse power.
The office of a boiler is to make steam and its real efficiency or the measure of its utility to the purchaser is measured by the amount of water it can turn into steam in a certain length of time and the amount of coal it requires to do this work.
An ordinary 54″×16′ boiler with forty 4″ tubes, 25 sq. ft. of grate surface and 800 sq. ft. of heating surface, in a general way is a 75 h. p. boiler, but good practice will get from it 100 h. p., and the very best modern engines 200 h. p.