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I would be grateful for any input on the best way to soundproof a noisy flue pipe that runs vertically through a corner of my bedroom. I know it's not an audio/visual issue but I was hoping to draw on the acoustics expertise in this forum. The pipe is the boiler exhaust flue pipe which runs through the house up to the roof and makes loud banging noises (loud enough to wake us up in the middle of the night) due to thermal expansion/contraction every time the heat turns on or off.

Currently, the pipe is enclosed in a drywall chase. Due to its location in the corner right next to a window, there is extremely limited space in which to add sound insulating thickness (hence my dilemma) -- see the attached photo and diagram. There is less than an inch of space between the pipe and the window moulding.

My current plan is to take down the drywall enclosure, stuff in as much mineral wool batting as I can fit into the cavity around the pipe, then rebuild the enclosure using 1/2" QuietRock drywall. If it can fit, I would add a second layer of QuietRock with Green Glue in between the layers, but I don't think there is sufficient room between the pipe and the window moulding for a double layer.

Would this work? Are there better ways to go about this? I'm willing to spend whatever it takes (given that our sleep is at stake) but the space limitations seem to be my biggest impediment to achieving meaningful noise reduction.

Thank you so much for any feedback.


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As a home owner that needs to do the same thing to a heating duct...

I have been thinking the banging might either be improper support or pipe wrap is needed. I would take out that whole section of wall and use strapping to buckle it down. Being very careful not to push the stack up or down don't create a leak at any joints (CO2 infiltration). Could also use mastic paste on any joints while your at it.

If someone more knowledgeable differs, please listen to them.
 

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I would also try to close in the back of the pipe area, so the sound doesn’t flank your new soundproofing. You might have to bite the bullet and slice off some of that window trim.
 

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Discussion Starter #7
Thank you all for the feedback.

I have been thinking the banging might either be improper support or pipe wrap is needed. I would take out that whole section of wall and use strapping to buckle it down.
Based on my research into the thermal expansion/contraction issue, it seems more likely that the opposite factor could be the cause of the noise (ie, the pipe being too tightly fixed in place, leaving insufficient flexibility for expansion/contraction). But I've already done everything I can (without yet removing the drywall enclosure around the pipe) to try to address the cause of the noise, all to no avail, which is why I'm now resorting to a sound attenuation solution (assuming I'm not able to stop the cause of the noise once the drywall is open).

You could even put the second layer up until it butts up against the trim, 100% coverage isn't required to dampen panel vibrations
Let's say I am willing to cover some or all of the trim. What I would prefer to do is first start with one layer, see if it provides enough sound insulation, and then only if not proceed to add more layers that start covering the trim. But if I knew the trim were going to get covered anyway, would there be a more effective solution than simply adding multiple layers of drywall? Like having a bigger cavity of insulation around the pipe?
 
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