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Boiler Horsepower & Steam Output Calculator Thermal & HVAC Systems
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Boiler Horsepower & Steam Output Calculator

Convert boiler horsepower (BHP) into actual steam generation (lbs/hr), thermal output in BTU and kW, factor of evaporation, and fuel firing input requirements.

1 BHP = 34.5 lbs steam/hr from & at 212°F
Header operating pressure
Deaerator output ~225°F
Higher Heating Value (HHV)
Actual Operating Steam Generation
8,358 lbs / hr
Rated: 8,625 lbs/hr (From & At 212°F)
Gross Heat Output
8,369 MBH
2,452 kW Electrical Eq.
Fuel Input Required
10,206 MBH
10,006 SCFH Natural Gas
Factor of Evaporation (FE): 1.032
Steam Saturation Temp: 353.1 °F
Latent Heat of Vaporization (hfg): 868.2 BTU / lb
Make-Up Water Feed Rate: 16.7 GPM
Daily Fuel Energy Consumed: 2,449 Therms / Day
ASME Power Boiler Standards: 1 Boiler HP is defined as 33,475 BTU/hr heat absorption rate into water.

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Boiler Horsepower, Steam Generation & Factor of Evaporation

Unlike mechanical horsepower (550 ft-lb/sec = 745.7 Watts), Boiler Horsepower (BHP) is a thermodynamic thermal rating established in 1876 at the Philadelphia Centennial Exhibition. By definition, one boiler horsepower is the evaporation of 34.5 pounds of water per hour from a liquid temperature of 212°F into saturated steam at 212°F (atmospheric pressure). This equates to an energy output of exactly 33,475 BTU/hr (9.8095 kW).

Thermodynamic Equations & Factor of Evaporation

  1. Factor of Evaporation (FE):
    In real industrial boilers, feedwater enters cooler than 212°F, and steam is generated at elevated pressure, requiring more heat energy per pound of steam than the standard benchmark:
    FE = (h_steam - h_feedwater) / 970.3
    Where h_steam is total enthalpy of saturated steam (BTU/lb), h_feedwater is enthalpy of liquid water at inlet temp (≈ T_feed - 32), and 970.3 BTU/lb is the latent heat of vaporization at 212°F.
  2. Actual Steam Output (lbs/hr):
    Actual Steam (lbs/hr) = Rated Steam (From & At 212°F) / FE = (BHP × 34.5) / FE
  3. Gross Heat Output (MBH = 1,000 BTU/hr):
    Heat Output (MBH) = BHP × 33.475
  4. Fuel Firing Input Rate:
    Fuel Input (BTU/hr) = (BHP × 33,475) / (Efficiency % / 100)

Frequently Asked Questions

Why does higher feedwater temperature increase actual boiler steam output?

When feedwater is preheated (e.g. from 60°F city water to 225°F in a pressurized deaerator), the boiler burner does not have to expend sensible heat warming the water up to saturation. Every BTU saved from feedwater preheating goes directly into boiling water into steam, increasing steam production by approximately 1% for every 10°F rise in feedwater temperature.

How many pounds of steam per hour does 1 BHP produce?

At standard benchmark conditions (212°F feedwater at 0 psig), 1 BHP produces exactly 34.5 lbs/hr. Under common plant conditions (125 psig steam with 220°F deaerated feedwater, FE ≈ 1.03), 1 BHP yields approximately 33.4 lbs/hr of actual steam.

What is MBH in boiler ratings?

MBH stands for Thousands of BTU per Hour (M = 1,000, BH = BTU/hour). 1 BHP = 33.475 MBH. For example, a 250 BHP commercial boiler produces 8,369 MBH (8,368,750 BTU/hr) of gross heat output.

How is natural gas consumption calculated for a steam boiler?

Divide total gross BTU/hr output by thermal efficiency (e.g. 82%), then divide by the heating value of natural gas (approximately 1,020 BTU per standard cubic foot). A 250 BHP boiler consumes approximately 10,000 SCFH of natural gas at full firing load.