We’ve had a few questions lately about the need for installation of a thermal expansion tank when a water heater is replaced. Some of the confusion seems to be whether or not this is a code requirement. While in some parts of the country an expansion tank is now required whenever a water heater is installed, including water heater replacement, that isn’t the case in Phoenix, Arizona. The code in Phoenix, and the Phoenix metro area, requires installation of an expansion tank only where a residence has a closed water system.
A closed system is one where something, such as a check valve like those used on a circulating line, or (in some cases) a pressure regulating valve*, will prevent expanding hot water from feeding back into the cold water supply. As hot water expands the pressure increases due to thermal expansion, and if a closed water system prevents relief of this increased pressure, it can create problems with the water heater’s temperature and pressure (T&P) relief valve, the valve at the side of the water heater that’s designed to open and release water when the pressure increases beyond a certain psi. The T&P valve may start to drip, as the water in the tank, under continual high pressure, seeks an outlet. Or, high water pressure may cause the T&P valve to be tripped open on a frequent basis. This not only puts excessive wear on the valve, but if the T&P drain line isn’t piped to the outside of the house, it it’s tripped and releases the water in the tank, it could flood your home.
Even more serious, excessive wear can cause the T&P valve to fail (a potentially dangerous situation. If the T&P valve fails, excessive build up of pressure in the water heater can cause the heater to explode.)
An expansion tank will allow for the relief of pressure due to thermal expansion in the water heater without causing the T&P valve to trip, drip, or fail prematurely. So, whenever you have a closed water system, you absolutely need to have an expansion tank installed. This is a code requirement designed to ensure your safety.
Questions about an expansion tank, or any other water heater repair? Give us a call. An experienced plumber is always available during business hours to answer your questions.
Stevens Plumbing Heating & Air Conditioning
*The pressure regulating (also called pressure reducing) valves we install have a bypass feature which prevents them from creating a closed system.