What type of valves must be installed on the water supply pipe to every water heater?

The requirement for installing full-open valves on the water supply pipe to every water heater is grounded in safety and functionality principles. Full-open valves allow for the maximum flow of water, ensuring that the water heater has adequate supply both for efficiency and to meet the hot water demand.

In terms of functionality, full-open valves facilitate easier maintenance and service, allowing for quick access during repairs or replacements without significant pressure loss along the line. This characteristic is crucial, particularly in emergencies where an immediate shut-off might be required to prevent damage or hazards.

Additionally, the design of plumbing systems often requires that valves be fully opened or closed to prevent potential backflow or pressure issues. Therefore, full-open valves are the best choice generally specified by plumbing codes, as they provide robust performance and safety when dealing with appliances like water heaters.