Thermal Expansion

Bradford White is pleased to announce that we have a new “Thermal Expansion” brochure.  This new brochure will help our customers better understand why thermal expansion occurs in water heaters and how to control it.  Thermal expansion is a term used to describe the circumstance of water expanding in volume as it is heated. 

All water heaters, regardless of heat source (gas, oil, electric, solar, geothermal, or indirect), can suffer the effects of thermal expansion.  This increase in volume and pressure must be relieved in some way.  The installation of a thermal expansion tank in the cold water line of the water heater can protect the system from the damaging effects of thermal expansion and increased pressure.  There are other options for pressure relief besides expansion tanks, but, unlike an expansion tank, they do not prevent the loss of water.

Please be advised that a Temperature and Pressure Relief Valve (T&P) is not a thermal expansion device.  In the normal operation of a water heater and T&P valve, water should not be discharged from the valve.  When the T&P valve discharges water it’s an indication of an abnormal condition in the system.  By discharging, the T&P valve is meeting its designed safety purpose.

Sometimes, damage to the water heater can occur before the T&P valve has a chance to open and relieve the pressure and lower the volume.  Fast acting solenoid valves on appliances (washing machines, dish washers) and some plumbing fixtures can create an instantaneous pressure spike that exceeds the rating of the water heater.  This can cause the tank to be damaged.  If a water heater is installed in a closed water supply system, such as one having a back-flow preventer in the cold water supply, provisions must be made to control thermal expansion. 

Pressure damaged tanks due to improper installation are not covered under the manufacturer’s warranty.  The International Plumbing Code (IPC), Uniform Plumbing Code (UPC), and Standard Plumbing Code all require thermal expansion control to be addressed.  Installing a properly-sized and charged thermal expansion tank in a water heating system is one recommended way to eliminate the problems associated with increasing volume and pressure in a closed or restricted plumbing system.  Another option would be to install a specialized relief valve in the plumbing system that is specifically designed to limit high pressure and prevent the problems associated with thermal expansion. Please be advised that installing the aforementioned relief valve may meet the plumbing code requirements, but it may also reduce the efficiency of your plumbing system, due to the loss of water.

PB 122706

PB 122706