Noisy Pipes

Newbie question..... Does the change in outside temperatures affect plumbing pipe noises in the wall? When an upstairs toilet is flushed, I hear a knocking noise in the walls. It's not a drip, it's a knock. It seems, however, that I'm now hearing a knocking noise when I flush any toilet in our home (two story). I had a plumber out initially who advised that it wasn't a leak/drip but rather a pipe that probably wasn't fastened. I have an associate who's a plumber that said the same thing. We have no evidence of water damage, leaks etc. but it seems to be more prevalent now that we have colder temperatures. Can colder outside temps (teens) affect plumbing noises? Help.
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Yes. My house pipes are quiet during the summer but noisy during the winter.

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Certainly. The pipes expand and contract with changes in temperature. And it doesn't even have to be the pipes. Perhaps something else is moving because of the temperature and coming in contact with the pipes.
I was curious so I looked it up. Copper has a coefficient of expansion of 9.3x10^-6 in/in per deg. F. What this means is that if the temperature rises by one degree F, each inch of copper will expand 9.3x10^-6 inches. Steel is 7.3.
A small amount, sure, but when pipes are going from 90F days to 20F (?) days it could be enough to move a pipe away from a 2x4 stud and allow it to bang. On the scale of bridges and such the expansion can be amazing.
I was astounded that CPVC pipe is 34. And ABS is 55!
Mike
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The comparitive coefficients are very interestin. Thanks for sharing. TB
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More likely to be the house around the pipes contracting in the cold. The pipes are subject to the temp of the water inside the pipe which is reletively constant yearroud. Though it is complicated by the fact that the water in the pipes will probably cool lower than in the summer when not flowing.
Does the banging stop once the water has flowed for a few minutes?
Pipe expansion/contraction is most often heard as a ticking sound in the walls during/after using the water.
If this did not happen last year, you can assume that something changed other than the weather.
Do you have galvinized steel pipes. I have an obstruction in one pipe that sounds like a machine gun going off inside.
Is the banging constant or a sharp bang when the flushing starts and stops, if so a water hammer device may be waterlogged. Try draining all the pipes and refilling the system to restore the air gap.
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Amazing info - thanks !
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plumbing
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It could be just a case of air hammer, caused by no air in the system water dose not compress so the air acts like a shock absorber. They might of piped air chambers in the system. ( it's a good practice) What you need to do is turn the water off drain all the water out and then refill. In time the water absorbs the air and you lose your cushion. Cost nothing can't hurt you never know might solve the problem.
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