# Boiler Capacity

## Steam boilers output can be expressed in Boiler Horsepower, MBTU or in Pounds of Steam delivered per hour

Boiler load - the capacity of a steam boiler - is often rated as boiler horse powers, 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 (1)

where

W = boiler capacity (Btu/h, kW)

h_{g}= enthalpy steam (Btu/lb, kJ/kg)

h_{f}= enthalpy condensate (Btu/lb, kJ/kg)

m = steam evaporated (lb/h, kg/s)

### Boiler Horsepower - *BHP*

The Boiler Horsepower (BHP) is

- the amount of energy required to produce
*34.5 pounds*of steam per hour at a pressure and temperature of*0 Psig and 212*, with feedwater at^{o}F*0 Psig and 212*.^{o}F

A BHP is equivalent to *33,475 BTU/Hr or 8430 Kcal/Hr *and it should be noted that a boiler horsepower is *13.1547* times a normal horsepower.

*1 horsepower (boiler) = 33445.6 Btu (mean)/hr = 140671.6 calorie/min (thermo) = 140469.4 calorie (mean)/min = 140742.3 calorie (20*^{o}*C)/min 9.8095x10*^{10}*erg/sec = 434107 foot-pound-force/min = 13.1548 horsepower (mech) = 13.1495 horsepower (electric) = 13.3372 horsepower (metric) = 13.1487 horsepower (water) = 9809.5 joule/sec = 9.8095 kilowatt*

Horsepower* (hp)* can be converted into* lbs *of steam by multiplying hp with* 34.5*.

#### Example - Boiler Horsepower to lbs of Steam Conversion

200 hp x 34.5 = 6900 lbs of steam per hour

Lbs of steam can be converted to hp by dividing lbs steam per hour by 34.5

#### Example - Lbs of Steam to Boiler Horsepower Conversion

5000 lbs of steam / 34.5 = 145 hp boiler

### Converting Boiler Horse Power (BHP) to kBtu/hr

Boiler Horse Power(BHP) | (kBtu/hr) |
---|---|

4.5 | 151 |

6 | 201 |

9 | 301 |

15 | 502 |

20 | 670 |

30 | 1004 |

45 | 1507 |

50 | 1674 |

60 | 2009 |

70 | 2344 |

80 | 2678 |

100 | 3348 |

*1 BHP = 33479 Btu/hr**1 Btu/hr = 0.293 Watts*