The minimum size trap arm for a bathtub is _____ inches.

The minimum size trap arm for a bathtub is established to ensure adequate drainage and to prevent issues such as clogs and backups in the plumbing system. A trap arm is the section of pipe between the bathtub’s drain and the trap itself, and its size directly affects the flow rate and capacity of waste water.

Choosing a 1 1/2 inch size is considered sufficient because it allows for a less restrictive flow of water and helps accommodate the volume of waste typically generated by bathtub usage. This size also aligns with standard plumbing practices and codes, which take into account the need for proper drainage to maintain hygiene and prevent odors from escaping into living spaces.

In contrast, smaller sizes like 1 inch or 1 1/4 inches might lead to insufficient drainage capacity, increasing the risk of clogs due to the higher likelihood of the waste water backing up, especially in a situation where multiple fixtures may be draining simultaneously. Additionally, the larger option of 2 inches is typically reserved for greater demands, such as those found in multiple fixture applications or larger installations.

Thus, 1 1/2 inches represents a balanced choice that meets regulatory requirements while ensuring efficient drainage for a bathtub.