What features must whirlpool and other bathtubs have?

Whirlpool and other bathtubs are required to have specific features that ensure functionality and safety. One essential requirement is the inclusion of a water-tight stopper, which prevents water from draining out of the tub when it is filled. This feature is vital for the intended use of the tub, especially for whirlpool units that often rely on retaining water for therapeutic purposes.

Additionally, a minimum drain size of 1-1/2 inches is typically mandated to ensure proper drainage and prevent clogging. This size allows for adequate water flow and prevents overflow during use, which is particularly important in bathtubs designed to hold significant volumes of water, such as whirlpool tubs.

The other options, while they include features that can enhance user experience or safety, do not represent mandatory requirements for whirlpool and bathtubs in general. Therefore, the combination of a water-tight stopper and a minimum 1-1/2 inch drain is the most accurate answer regarding essential features for these installations.