Water hammer and banging in your pipes

by Gilbert Migirditsian, professional engineer, home inspector, and founder of GM Inspection

Do you often wonder what that loud “bang” is when you suddenly close the faucet or flush the toilet? Did you know this is known as water hammer and is actually pretty common. This may also be air in the pipes if the sound is caused when a pumping device (like a septic pump) starts up but may be water hammer nonetheless. When looking at the causes of water hammer, three factors come into play: a) the length of the pipe, b) the speed at which the flow of water is interrupted, and c) the speed of the valve closing. Now it is not possible to act on all issues affecting water hammer, for example the length of the pipe which can’t be controlled, but what are some simple solutions to apply? Obviously, if the problem is caused by opening and closing faucets, doing so very slowly will definitely help but does not act at the source of the problem. If the noise is caused when a washing machine or dishwasher starts, the simplest solution is to install a water hammer arrester on both valves connecting hot and cold water to the device. Installing air chambers, in my opinion, won’t help much most of the time and you may actually make the problem worse. If all else fails, the end solution is replacing the section of pipe causing the water hammer with a larger one (for example, replacing 5/8 inch pipe by 3/4 inch pipe for the problem section).

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