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.