What is the smallest pipe size that can be concealed in a wall?

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

Answer: (B)

Gas piping inside walls is limited to a minimum size to ensure adequate supply, manageable pressure drop, and safer maintenance. The smallest size permitted to be concealed in a wall is 1/2 inch. A 1/4 inch line is too small for typical residential gas distribution and is generally restricted to appliance connectors or exposed runs, not concealed behind wall surfaces, because it wouldn’t reliably supply appliances and would be harder to detect leaks. Larger sizes, like 3/4 inch or 1 inch, can be concealed when installed to code with proper supports and clearances.