Boiler Horsepower to Steam Rate

This is the form a water treater uses, because chemical feed, blowdown and makeup all scale with pounds of steam rather than with BTU. A 200 BHP boiler makes 200 × 34.5 = 6900 lb/h of steam, which at 8.34 lb per gallon is roughly 14 gpm of feedwater, and that single conversion sizes the softener, the chemical pump and the condensate receiver in one step.

Remember the qualifier hiding in the definition: 34.5 lb/h is "from and at 212 °F", meaning water already at boiling with only latent heat to add. Feed the same boiler with 60 °F makeup at 100 psig and it will deliver closer to 30 lb/h per BHP, because part of the fuel is going into sensible heating and into the higher latent heat at pressure. Manufacturers publish a "factor of evaporation" for exactly this correction. For treatment arithmetic the 34.5 figure is fine: it is conservative in the right direction, sizing the water side slightly generously.