Steam is a gas generated by heating water to a temperature bringing it to the boiling point. When this happens, water changes its physical state and vaporizes, turning from a liquid into a gas. Conversely, when heat energy is removed from steam, it loses its ability to retain a gaseous state and condenses back into a liquid (condensate). The temperature at which condensation takes place is known as the dew point.

Boiler Ratings and Boiler Load

• Boiler load - The horsepower, lbs of steam per hour, or BTU is the rating indicating the maximum capacity of a boiler. When a boiler operates at its maximum rated capacity, it is referred to as maximum load. If the load varies from hour to hour, it operates at a varying load. Load and load variations can influence the amount of chemicals required for treatment and the treatment controls required.
• The oldest method of rating boilers, still used to rate small boilers, is by horsepower (hp). One horsepower is defined as the ability to evaporate 34.5 lbs of water into steam at 212 deg. F and above.
• Large boiler capacity is generally given in lbs of steam evaporated per hour, under specified steam conditions. Maximum continuous rating is the hourly evaporation that can be maintained for 24 hours.

1. To convert horsepower (hp) into lbs of steam: Multiply hp x 34.5

Example: 100 hp x 34.5 = 3450 lbs of steam per hour

2. To convert lbs of steam to hp: Divide steam per hour by 34.5

Example: 8625 lbs of steam ÷ 34.5 = 250 hp boiler

3. To convert BTU into hp, divide the BTU rating by 33,472 - (33,472 BTU equals 1 hp)

Example: 8,368,000 BTU ÷ 33,472 = 250