What is the required water design capacity of bathtub mixing valves in gallons per minute?

The correct answer reflects the International Plumbing Code standards, which specify that the required water design capacity for bathtub mixing valves is typically set at 4 gallons per minute. This capacity is based on the idea that a bathtub should be filled in a reasonable amount of time to ensure user comfort and convenience.

Mixing valves blend hot and cold water to deliver water at a consistent and safe temperature, which is especially important in preventing scalding and ensuring a pleasant bathing experience. The specified flow rate allows for sufficient water volume to fill the tub, catering to standard bathing practices and the average size of bathtubs in use.

Other flow rates, such as 2, 3, or 5 gallons per minute, may not align with the optimal performance needed for a bath, either being inadequate for filling the tub in a timely manner or exceeding what is necessary, which could result in wastage of water. Adhering to 4 gallons per minute ensures a balance between user needs and efficient water use.