Water Heater T&P Relief Valve (Temperature & Pressure Relief Valve) 101

More About T&P Relief Valves:

• This safety feature “[…] was designed as an emergency relief device only.” Operating a water heater without an additional protectorate from thermal expansion such as a thermal expansion tank, “the T&P valve could be subject to reduced effectiveness or failure”
• Most water heater manufacturers and local plumbing codes not only require the installation of a thermal expansion tank, but also a discharge pipe: a copper line that is meant to guide any discharge water from the water heater down towards the ground, ideally near a floor drain.
• It is important not to confuse the T&P Valve with the drain valve, pressure relief valves, nor pressure reducing valves (PRVs).
• What is the difference between a T&P Valve and a Pressure Relief Valve?: “While temperature and pressure relief valves required to be installed on the water heater are mechanical devices that relieve overheated water or excessive pressure, they cannot maintain a consistent pressure. The installation of a thermal expansion tank is the only device recommended to maintain a constant safe operating pressure” (Source: A.O. Smith) 

Why is Protection from Thermal Expansion Important?

Thermal expansion refers to the process of water's volume and contained pressure increasing as a result of the water heating process.

“Thermal expansion of water, if not compensated for in system design, will lead to the early failure of components. These failures are not covered by the manufacturer’s warranty, so it is extremely important that everyone be aware of the causes, symptoms and solutions to thermal expansion in a closed water heating system” (Source: A.O. Smith)