A pressure relief valve is required when what is installed?

A pressure relief valve is specifically required when a water heater is installed. This device is crucial for safety because it helps to prevent excessive pressure buildup within the water heater. As water is heated, it expands, increasing the internal pressure. Without a pressure relief valve, this pressure could become dangerously high, potentially leading to equipment failure or even explosion.

While a water pressure regulator plays a role in managing the water pressure entering a system, it does not directly require a pressure relief valve for its operation. Instead, it controls the pressure and ensures that the downstream systems do not receive excessive pressure. Therefore, it's the installation of the water heater that necessitates the inclusion of a pressure relief valve to ensure safe operation.