Boiler Horsepower, Steam Output, and EDR
The ABMA / ASME boiler ratings from a gross output: BHP = output / 33,475, steam = BHP x 34.5 lb/hr 'from and at' 212 F, and EDR = BHP x 139 sq ft. A 500,000 Btu/hr boiler is 14.9 BHP, 515 lb/hr, and 2,076 sq ft of radiation. The one-line conversion between how boilers are rated (Btu/hr, BHP) and what they cover (steam, EDR). The 'from and at 212 F' basis assumes 212 F feedwater at 0 psig; apply the maker's factor of evaporation for real conditions.
Formula and source
boiler_hp = output_btuhr / 33,475; steam_lbhr = boiler_hp x 34.5; edr_sqft = boiler_hp x 139. From the ABMA / ASME definition: 1 boiler horsepower = 33,475 Btu/hr gross output = 34.5 lb/hr of steam evaporated 'from and at' 212 F = 139 sq ft of equivalent direct radiation.
ABMA / ASME boiler-horsepower definition (33,475 Btu/hr; 34.5 lb/hr from and at 212 F). Not edition-bound.
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