Roy City Public Works Department

Thermal expansion occurs when cold water is heated in a residential water heater and the water expands so much it has nowhere to go in a closed water system. Thermal expansion over time can damage your dishwasher, washing machine, and other water connections and appliances in your home. The International Plumbing Code, as adopted by the State of Utah and DOPL, requires a thermal expansion tank to be installed on every water heater, regardless of the existence of dual check backflow preventers.

International Plumbing Code 607.3
Thermal Expansion Control:
Where a storage water heater is supplied with cold water that passes through a check valve, pressure-reducing valve or backflow preventer, a thermal expansion control device shall be connected to the water heater cold water supply pipe at a point that is downstream of all check valves, pressure-reducing valves, and backflow preventers. Thermal expansion tanks shall be sized in accordance with the tank manufacturer’s instructions and shall be sized such that the pressure in the water distribution system shall not exceed that required by Section 604.8.

A thermal expansion tank is a small tank that contains a bladder to expand as the pressure increases to prevent damage to the water heater, appliances, and other plumbing devices on your private water system. We encourage all Roy City Water customers to check your water heater for a thermal expansion tank and get one installed in compliance with plumbing code to prevent damage to your home.

If you have questions or concerns, please call Roy City Public Works 801-774-1090.