Smallest permitted dimension for an air supply duct according to B149.1 Code, Clause 8.3.2.

Smallest permitted dimension for an air supply duct according to B149.1 Code, Clause 8.3.2.

• A. 3 inches
• B. 6 inches
• C. 9 inches
• D. 4 inches

Answer: (B)

Air supply ducts must provide enough air for safe combustion and proper appliance operation. The B149.1 Code sets a minimum size for these ducts to ensure there’s sufficient air flow; anything smaller could restrict air and create safety issues. The smallest permitted dimension is six inches, so you could use a six-inch duct or larger, but not smaller. Among the options, six inches is the correct minimum. The other smaller sizes don’t meet the requirement, while a larger size like nine inches is allowed but not the smallest.

Air supply ducts must provide enough air for safe combustion and proper appliance operation. The B149.1 Code sets a minimum size for these ducts to ensure there’s sufficient air flow; anything smaller could restrict air and create safety issues. The smallest permitted dimension is six inches, so you could use a six-inch duct or larger, but not smaller. Among the options, six inches is the correct minimum. The other smaller sizes don’t meet the requirement, while a larger size like nine inches is allowed but not the smallest.