Thermal Expansion tank requirements

A thermal expansion tank is required throughout most parts of Kansas City when you are installing a new water heater. It’s usually a good idea to measure your water pressure to determine the need for an expansion tank.

A thermal expansion tank is required by the water heater manufacturer if your house is on a closed loop system. A house that has a PRV is considered to be a closed loop, even though most PRV’s have a bypass. A closed loop is also created when there is a check valve in the water meter.

What is thermal expansion?

When water is heated from room temperature to 120 degrees it causes the water to expand, just like when it freezes. This is referred to as thermal expansion. When 40 gallons of cold water is heated up to 120 degrees or greater it expands to 40.6 gallons. If this additional volume does not have anywhere to go it will increase the pressure inside the plumbing system.

Proper installation of Thermal Expansion tank

A thermal expansion tank should be installed on the cold water line between the water heater shutoff and the water heater inlet. A thermal expansion tank must also be supported. If there is a wall behind the water heater it can be installed like the picture on the left. In order to properly support the expansion tank it may be necessary to install the tank before the water heater shutoff supply.

PRV’s and Expansion tanks go hand in hand

In order for the Expansion tank to work properly it needs to be calibrated to match the incoming water pressure. A PRV will set the water pressure to a specified amount and the expansion tank is inflated to slightly exceed that amount. When the water pressure is too high, the expansion tank will fill with water and fail quickly.

thermal expansion tank requirements in Kansas City

These pictures below are indicators the existing expansion tank has failed and needs to be replaced. Thermal expansion tanks can fail in a more catastrophic fashion than the water heater.

It’s recommended that expansion tanks be inspected every year and replaced every 7 years. Installing a PRV and setting the pressure can help you worry less about the thermal expansion tank maintenance.