Thread: Client Complaining of Loud Knocking Noises

I'm providing the actual question from the client: This is new construction

"Whenever the hot water is running, there is a knocking in the walls. I had someone out that thought the problem was the temp of the hot water heater. We adjusted it down, yet the knocking is still occurring. Again, only when the hot water is running (showering, washing dishes, etc). Do you have an other ideas that we might want to consider?"

Additional info after I asked questions:

"The knocking occurs along the same wall (i.e. in the kitchen) only when hot water is being run on the top floor and the main floor. It occurs if you run the stackable washer/dryer, upstairs shower, sinks upstairs and the kitchen sink. That wall is opposite the location of the water heater....moreso along the wall where the water eventually goes to the sump pump/ejector/common sewer."

Thanks,

Sean

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Try Here http://www.siouxchief.com/Resource_/...FAQ%204-04.pdf

Nicely explained, thank you for that link

Steve

Originally Posted by Billy Stephens

Try Here http://www.siouxchief.com/Resource_/...FAQ%204-04.pdf

I'm going to say it's the plastic drain pipes in the wall and floor joists expanding. If the pipes are tight through the studs and joists they will make loud noises as the pipes expand lengthwise.

Could also be loose or unsupported supply lines " Rattling " inside the wall.
.

Originally Posted by Benjamin Thompson

I'm going to say it's the plastic ... pipes in the wall and floor joists expanding. If the pipes are tight through the studs and joists they will make loud noises as the pipes expand lengthwise.

I would agree if the word "drain" was replaced with "hot supply" as the description of the problem does not fit the water hammer reference Billy provided (but that is a good reference on water hammer).

I suspect the CPVC hot water branch supply piping is expanding in clamps which are too tight on pipes. As the CPVC expands, it is supposed to be allowed to move within the clamps, with the clamps too tight, you can hear the movement of the CPVC pipes in the clamps as it pushes it way through the clamps, then when it cools, the CPVC contracts and the process starts all over.

It would be easy enough to figure out which, try running the hot water with the drains plugged and see if the noise occurs.
You see alot of new houses with CPVC supply pipe in Florida?

I note the OP provies location as "chicago". I am not aware of the City of Chicago having approved CPVC as a hot water distribution system or potable water distribution material.

I vote for improperly secured or supported riser, impinged branch, closed system without expansion, or overly high operating pressures. Assuming the main to the WH is not impreperly tee-dropped in the first place.

Gentlemen,

Mr. Watson is correct. The supply piping is copper in this particular home. Thanks for all of the responses. This wasn't something that I identified during the inspection, why would it happen now?

We don't allow no stinkin' cpvc in this town.
I'd say no air chambers installed.

Something as simple as a pipe hanger might have been pulled out, say for example someone hanging something from the pipe, or not sufficiently nailed in, greener or wetter wood now drier, contracting pushing out the hanger. Or perhaps not using the correct hanger and the pipe is impinged where it changes direction and pipe moves as hoter water flows through it replacing the stagnant less hot water within.

Occupied use including fast closing/fast opening valves (dishwasher, washiing machine), the riser, unsupported starts rattling. Its also been colder lately, more severe temperature swings, inside, outside, and apparently in this plumbing wall cavity housing the riser.

Storage type WH assumed in basement.

I wouldn't first suspect failure to install air chambers, esp. in the areas described experiencing use related knocking, that's one thing I wouldn't expect to be overlooked in a Chicago plumbing rough on new construction; but instead that they may have "lost their air", dissolved, esp. if long time before actual first occupancy. Quickly can be determined by cutting off water draining the system (opening valves top and bottom floors), then recharging.

Even if "plastic" drain, waste, vent piping were present, I would not at this point suspect same regarding "knocking" since your additional information gathered indicates the knocking is present when the stackable clothes washer is filling with hot water, and generally when same is drawing hot water it is not discharging hot water, i.e. drainage at the same time.

Therefore, and in summary, I suspect either: a loose or missing lateral pipe hanger(or hangers) between the WH and the riser, or an improper, impingment where that long, expanding axially, lateral run changes direction to rise up the plumbing wall and/or impingement/restriction of that movement to/of the riser when heated; an improper horizontal tee off to same for supply; or the air chambers being saturated with water (easy test/fix).