Boiler loads, or the capacity of steam boilers, are often rated in boiler horsepowers, lbs of steam delivered per hour, or BTU.
Lbs Steam delivered per Hour
Large boiler capacities are often given in lbs of steam evaporated per hour under specified steam conditions.
BTU - British Thermal Units
Since the amount of steam delivered varies with temperature and pressure, a common expression of the boiler capacity is the heat transferred over time expressed as British Thermal Units per hour. A boilers capacity is usually expressed as kBtu/hour (1000 Btu/hour) and can be calculated as
`W = (h_g - h_f) m`
where