PVC pipe installed vertically requires a guide installed midway between required supports for pipe sizes _____ inch(es) and smaller.

The requirement for installing PVC pipe vertically involves specific guidelines to ensure the structural integrity and proper functioning of the plumbing system. For pipe sizes 2 inches and smaller, installing a guide midway between required supports is necessary. This helps prevent the pipes from sagging or bending under their own weight, especially when subjected to external forces or temperature changes that can lead to expansion and contraction.

By incorporating a guide, the movement of the pipe is controlled, which maintains alignment and reduces stress on the joints and fittings. For pipe sizes greater than 2 inches, the structural strength is usually sufficient to withstand these stresses without the need for additional supports. Therefore, the correct answer is based on the size threshold that justifies the use of additional guide supports to ensure the reliability of the plumbing system.