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Question DetailsAsked on 10/16/2016

Air ducts popping noise

Every now and the. I hear a popping noise in my air duct vent. When the vent makings a popping noise neither the heat or a/c is running. So,it is making the noise when the system is off. The only explanation I can think of is that the ductwork and vents run through the ceiling. I have cathedral ceilings so there is no attic space. There is just enough to space to run the ducts. Could it be that because the ducts and vent are so close to the roof that the popping noise is due to the metal expanding when it is not or restricti when it is cold? I have noticed the popping when it is both hot and cold. Once again it is just a single pop that is happens occasionally and I only notice it when the system is not running. The only vents and ducts I notice this in are the ones with the raises ceiling and not attire space. I also notice random popping noises in the raised ceiling. Is this just because they are close to the roof and are not as insulated as well as other parts of houSe

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2 Answers


Sounds like you have it tied down - I imagine you would find, if you noted the conditions eash time, that it occurs starting maybe 15-30 minutes after the sun hits that section of the roof, and again maybe an hour or few after the sun goes off that face of the roof - causing heating and cooling of the ducts. Should not hurt anything - could just be "diaphragm flexing" of the ducting - the expansion and contraction causing the flat faces of the duct to pop in or out of the flat plane as they contract and expand. That is commonly a very metallic sound, like someone hitting the duct with a hammer or a metallic pop as you are describing. Or could be the ducts slipping against hangers or joists, making a clunk or squeek or howl or ghost "creaking" type sound usually - sometimes somewhat or even almost totally different sound when expanding versus contracting.

I would guess this is always or almost always in daytime hours since you said it does not relate to whether the furnace is on ornot - though in some cases just the heating and cooling of the HVAC ducts will cause it too.

As long as the drywall on the ceiling is not coming loose or dropping pieces of joint compound (which would be indicative of joist or rafter issues), I would say no worries structurally - though if the framing is creaking like that, could be indicative that the ducts are poorly insulated and you are losing a fair amount of energy heating and cooling the attic.

To stop it, if desired because it is irritating (though may take a couple of cycles of finding all the spots making noise and may have difficulty reaching the trouble spots) : the diaphragm issue is usually cured (once you find the spots doing it) by putting a brace o bracket across the spot moving and shimming it against the duct with slip-on pipe insulation or felt weatherstripping - to hold the duct face that is "tin canning" in the inward position so it can't pop back and forth from "sucked in" to "bellied out".

Sliding ducting against framing or hangers you can stop with low-friction plastic padding or teflon-coated HVAC padding wrap between them, well secured to prevent it ripping off. DIY cheap way that does not last as long is duct tape padding, with the ends taped down well beyond the friction zone so it does not grab the ends and peel it off and bunch it up when moving. Glossy side of duct tape against the ducting if rubbing on bracket, taped to duct and glossy side against wood if touching framing.

Answered 4 years ago by LCD



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