Water hammer arrestors

Attention: Home builders and plumbing contractors

Effective January 1, 2017, manufactured water hammer arrestors shall be installed within all water distribution systems serving residential units.  This will apply to all building permit applications submitted after December 31, 2016.

Built-in-place air chambers on tub and shower valves will no longer be required.  However, at least one manufactured water hammer arrestor will be required on both hot and cold water lines.  It is recommended that these devices be installed on washing machines lines, but can be installed anywhere within the water distribution system.

Manufactured water hammer arrestors shall be accessible at time of final inspection.


Water hammer is a condition that occurs in a pressurized plumbing pipe caused by the sudden stoppage of flow.  Quick closing valves such as solenoid valves used on washing machines, dishwashers and ice makers are the main cause of water hammer in residential dwellings.  Manufactures of pipes and fittings will not warranty their products damaged by water hammer since they’re not tested to these extreme pressures.

Manufactured water hammer arrestors have not always been available. When they were first introduced into the market they were not certified and were very expensive. Many plumbing professionals developed air chambers to try to correct the damage caused by water hammer.  These air chambers, when sized correctly and installed at the high point, did work.  However they often became water logged, resulting in the entire system needing to be drained to allow the air back into these chambers.

Manufacturers now have certified devices to control water hammer. These devices are intended to outlast the plumbing system without any need for maintenance.

For more information

Peter Pieczewski, Plumbing Inspector
519-837-5615 extension 2733
[email protected]