- Heat output
- 3,347,500 Btu/h
- Heat output
- 981.0 kW
- Steam, from and at 212 °F
- 3,450 lb/h (1,565 kg/h)
- Actual steam at 100 psig, 180 °F feedwater
- 3,214 lb/h (1,458 kg/h)
The short answer
One boiler horsepower (BHP) is 33,475 Btu/h of heat output, which evaporates 34.5 lb (15.65 kg) of water per hour from and at 212 °F (100 °C), or about 9.81 kW. Actual steam output at operating pressure with colder feedwater is lower, so size from the steam you need at your conditions.
Formula
Heat output (Btu/h) = BHP × 33,475Output (kW) = BHP × 9.8095Steam “from and at 212 °F” (lb/h) = BHP × 34.5Actual steam (lb/h) = BHP × 33,475 ÷ (h_steam − h_feedwater), with enthalpies in Btu/lb
How to use it
- Pick what you know: boiler horsepower, kW, Btu/h or steam flow.
- Enter the feedwater temperature and steam pressure for an actual (not “from and at”) steam rate.
- Read the equivalent ratings and the actual steam output at your conditions.
Assumptions
- Saturated steam; enthalpies are interpolated from steam tables and are accurate to about 0.5 %.
- Output ratings, not fuel input. Divide by the boiler’s fuel-to-steam efficiency for fuel input.
Frequently asked questions
How many lb/h of steam is one boiler horsepower?
34.5 lb/h “from and at 212 °F”, meaning feedwater at 212 °F turned into steam at 212 °F (0 psig). At 100 psig with 180 °F feedwater, one BHP makes about 32 lb/h because each pound needs more heat.
How many kW is a boiler horsepower?
About 9.81 kW of heat output (33,475 Btu/h). It is not the same as mechanical horsepower (0.746 kW).
How do I size a boiler from steam demand?
Add up the peak steam demand in lb/h at operating pressure, convert it to heat using the enthalpy rise from feedwater to steam, divide by 33,475 to get BHP, then add margin for start-up loads and future growth.