What is the minimum discharge pipe size for a water heater?

The minimum discharge pipe size for a water heater is 3/4 inch. This size is specified to ensure adequate drainage capacity and to prevent the risk of excessive pressure buildup in the system. A 3/4 inch discharge pipe can handle the volume of water effectively, especially in the event of a relief valve activation, which is critical for safety in preventing potential scalding or water damage.

Using a smaller size, such as 1 inch or 1/2 inch, may not provide sufficient flow, leading to potential hazards during a discharge event. Similarly, a discharge pipe size of 2 inches is unnecessarily large for residential water heaters, which could complicate installation and increase costs without providing significant benefits. Thus, 3/4 inch is the recognized standard within the plumbing code for effectively accommodating the discharge from water heaters.