How is draft in a boiler system typically measured?

In a boiler system, draft is measured in inches of water column. This measurement reflects the pressure difference between the inside of the boiler and the outside atmosphere, which is essential for determining the efficiency of combustion and ensuring proper venting of gases.

Using inches of water allows for a clear understanding of the subtle differences in pressure that are crucial for maintaining optimal draft conditions. Since the pressures involved in draft measurements are typically low, this unit effectively conveys the slight variations that can significantly affect the performance and safety of the boiler system. The other options, such as pounds per square inch or degrees Fahrenheit, pertain to different aspects of boiler operation—pressure and temperature, respectively—rather than to the draft itself, while centimeters of mercury is more commonly used in other contexts of pressure measurement but not typically in boiler draft scenarios.