Where should the TPR discharge pipe discharge through?

The TPR (Temperature and Pressure Relief) discharge pipe should terminate with an air gap to ensure safe and proper function. This design is crucial because the role of the TPR valve is to release excess pressure and temperature from a water heater, preventing potentially dangerous conditions that could lead to an explosion.

By discharging through an air gap, the risk of backflow into the water heater is mitigated, allowing any discharged hot water or steam to escape safely into the atmosphere. This prevents contamination of the potable water supply and ensures that the water heater operates safely. An air gap provides a physical separation between the discharge and the water supply, which is essential for maintaining safe plumbing practices.

Other options such as draining directly into a drain or wall outlet could lead to various hazards, including potential backflow or water damage, while discharging into an overflow tank could complicate systems unnecessarily. Thus, using an air gap aligns with plumbing safety standards and best practices.