The TPR discharge pipe should be installed so as to flow by _______.

The TPR (Temperature and Pressure Relief) discharge pipe must be installed to flow by gravity to ensure that any discharge from the water heater can drain effectively without blockage or backflow. Gravity drainage is essential for the proper functioning of the TPR valve, as it allows any excess pressure and temperature relief to escape freely, preventing potential hazards such as explosions or leaks.

When the TPR valve opens due to excess temperature or pressure, the discharge must be unimpeded to safely direct hot water or steam away from the unit and the surrounding area. Installing the discharge pipe in a way that allows gravity to assist with the flow significantly reduces the risk of backups and is in alignment with safe plumbing practices and building codes. Proper sloping of the pipe in the direction of the discharge point further enhances the effectiveness of this system.