It is very critical importance of getting a thermal expansion tank installed off your water heaters on the domestic water system. Since to newly county requirements of the installation of a dual check valve installed between the meter yoke and the pressure reducing valve on the water service from the street to the water connection inside you may need to install a thermal expansion tank. The county now wants a dual check installed because of contaminates caused by backflow feeding back to the main water supply in the street from houses and businesses that might affect the community from its contamination.
Before the installation of the dual check installed on water supply inside the home or business off the street main the water piping that was pressurized from water being heated up from the water heater due to expansion had a place to release pressure to the street that would not affect homes or businesses. Now with the installation of the dual check it makes it a closed system and if an thermal expansion tank is not installed this could lead to busted pipe inside the home or business, leaking faucets due to O-ring and seat washer failure, ruptured and distorted water tank, and causing the temperature relief off the water heater to drip. All these things could cause property damage if left undetected.
This is how a thermal expansion tank works when water is heated in a closed system it expands. Water is not compressible, therefore, the additional water volume created has to go someplace. When an expansion tank is installed the excess water enters the pre-pressurized tank. As the temperature and pressure reaches its maximum, the diaphragm flexes against an air cushion (air is compressible) to allow for increased water expansion. When the system is opened again or the water cools, the water leaves the tank and returns to the system. Some people believe the pressure relief valve will solve the problem with built up pressure due to expansion but it will not, built up of excessive pressure inside the tank can cause a fatal explosion especially when it comes a gas source in heating of the water.
The size of thermal expansion tanks comes in 2 to 5 gallon capacity which one to be used determines on the size of the water heater and the pressure coming from the street to the house or business of the system in which one is to be installed. The thermal expansion tank should be installed on the cold side of the water heater in the place in the vertical piping between the tank and shut off valve if possible this way if the valve is shut off you are still protected. Also in doing this it’s better to run copper then cpvc because of course copper is more ridge and have a better chance of the pipe breaking and using strap iron to support the load of tank. All of this should be sized and installed only by a licensed plumber in order to give you the right installation.