What is the maximum size of blow-off piping for a steam boiler with more than 100 ft² of heating surface?

What is the maximum size of blow-off piping for a steam boiler with more than 100 ft² of heating surface?

• A. 1 inch
• B. 1/2 inch
• C. 2 inches
• D. 3/4 inch

Answer: (A)

Blow-down piping is sized to safely carry away the water that is discharged during boiler blow-down, and the size is tied to how large the boiler is. When the heating surface exceeds 100 ft², the standard guideline allows the blow-off pipe to be up to one inch in diameter. This size is chosen as a practical balance: it’s large enough to handle the anticipated blow-down flow without excessive resistance, yet not so large that the drainage system must accommodate a much higher and harder-to-control discharge. Smaller boilers are restricted to smaller pipes, and much larger pipes aren’t needed for boilers in this size range. So, the maximum allowed size for a boiler with more than 100 ft² of heating surface is one inch.

Blow-down piping is sized to safely carry away the water that is discharged during boiler blow-down, and the size is tied to how large the boiler is. When the heating surface exceeds 100 ft², the standard guideline allows the blow-off pipe to be up to one inch in diameter. This size is chosen as a practical balance: it’s large enough to handle the anticipated blow-down flow without excessive resistance, yet not so large that the drainage system must accommodate a much higher and harder-to-control discharge. Smaller boilers are restricted to smaller pipes, and much larger pipes aren’t needed for boilers in this size range. So, the maximum allowed size for a boiler with more than 100 ft² of heating surface is one inch.