A knocking sound in your apartment is probably irritating all on its own, but being unable to identify its source makes things even more frustrating. I went to a pre-war building on the Upper East Side to determine the cause of such knocking inside two different apartments. The knocking sounded much like the bangs of a radiator when it’s initially turned on, so I decided to check out the radiators first. But the knocking noise seemed to resonate from within the apartment walls rather than the radiators themselves, and the noise only occurred in the morning around the same time the building’s steam system was turned on. Taking this fact into consideration, the problem became obvious to me: inside the wall was an exhausted expansion joint. The old joint would clank when the system’s pipes expanded and needed to be replaced.

Here’s what happens: expansion joints are built to allow the force of a hot, expanding pipe to exert its energy. Expansion joints defuse the natural tension brought on by the expanding pipe. If expansion joints are not installed and/or maintained, the force of the expanding pipe can exert its energy in different ways and cause damage to the heating system. If you hear knocking in your apartment and you can’t figure out its source, it could be due to an exhausted expansion joint.

By Spencer Kraus – Account Manager – Fred Smith Plumbing & Heating Co.