wrote in message
oups.com...
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


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.