Ductwork Banging/Popping

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Old 01-24-09, 08:41 PM
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Ductwork Banging/Popping

My ductwork has an issue where it makes a banging or popping noise when it expands or contracts. Its not coming from the furnace but definitely the ducts. I have a two storey home with a finished basement that is 7 years old. I have owned the house for 2 years and have had this issue the whole time. The previous owners said they had an HVAC guy look at the issue but were told that it isn't causing any damage so just live with it.

It seems to happen in the 1st level floor joists ( basement ceiling ). I've popped off some of the drop ceiling tiles and noticed that the ductwork sits on 2"x2" wooded crossers between the floor joists. Is this proper? I'm thinking that the expansion or contraction of my ducts resting on the wood reverberates through the floor joists making the rather loud banging noise.

Just to isolate the issue to ductwork, there are no cracks in my walls to indicate shifting foundation. Plus, I've noticed that when I raise or lower the temp the bangs become more frequent and when I keep the temp constant I may get one or two bangs per day.

Has anyone ever run into this problem before? Any suggestions would be greatly appreciated.
 
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Old 01-25-09, 03:35 PM
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The contractor that installed the duct went the cheap way! Most do! They did not cross break the metal or they did not use a heavy enough gauge. You could take some thicker metal and screw it to the bottom of the duct to help it be more ridged.
 
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Old 01-25-09, 03:59 PM
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Originally Posted by airman.1994 View Post
The contractor that installed the duct went the cheap way! Most do! They did not cross break the metal or they did not use a heavy enough gauge. You could take some thicker metal and screw it to the bottom of the duct to help it be more ridged.
Thanks for the reply. You say to screw thicker metal to the bottom of the duct. These are 5" circular metallic ducts. How exactly should I go about screwing the metal to the ducts? Also, what do you mean by "cross break the metal"? I've also heard that ducts should be supported by hangers whereas mine are supported by wooden crossers between the floor joists. Should I look into hangers or just leave them the way they are?
 
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Old 01-26-09, 05:29 PM
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So all you have is round duct and no square? If that is the case you will have to replace the round pipe. The wood is OK! Not the best but OK. Id say if the trash installer cut these corners what else did he do. I would have a good HVAC company come out and take a look at the system. Might save you lots of money in the long run.
 
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Old 01-27-09, 05:08 AM
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Originally Posted by airman.1994 View Post
So all you have is round duct and no square? If that is the case you will have to replace the round pipe. The wood is OK! Not the best but OK. Id say if the trash installer cut these corners what else did he do. I would have a good HVAC company come out and take a look at the system. Might save you lots of money in the long run.
I thought that round ductwork is normal. The main duct coming from the furnace is square but the duct pipes that branch off the main duct are round. These are the pipes that are sitting on wood and seem to be making the popping noise. Is there anything that can be done to the round ductwork to reduce popping? Thanks again.
 
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Old 01-27-09, 03:20 PM
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Never heard round pipe pop! Must be very light gauge. How about running a screw from the wood into the duct.
 
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Old 01-27-09, 03:33 PM
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Originally Posted by airman.1994 View Post
Never heard round pipe pop! Must be very light gauge. How about running a screw from the wood into the duct.
I may give that a try. It may be coming from the main square duct but I'm almost positive its the circular ducts making the noise. When you talk about cross breaking the ducts, what do you mean? Also the part about screwing more solid metal to the bottom, do mean to screw a sheet of metal or a rod? Thanks.
 
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Old 01-27-09, 06:38 PM
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I agree with airman, snap, crackle and pop of round duct just doesn't happen. Unfortunately it IS common with light-gauge rectangular duct.

What airman means by the term "cross breaking" (or braking) is that when the duct is bent up from a flat sheet of metal the brake (bending machine) is used to put slight creases in an X pattern across the wider section of the duct. It adds tremendous stiffness and prevents (in almost all cases) the duct from doing the snap, crackle and pop from changes in temperature and internal air pressure.
 
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Old 01-28-09, 07:50 PM
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Originally Posted by furd View Post
I agree with airman, snap, crackle and pop of round duct just doesn't happen. Unfortunately it IS common with light-gauge rectangular duct.

What airman means by the term "cross breaking" (or braking) is that when the duct is bent up from a flat sheet of metal the brake (bending machine) is used to put slight creases in an X pattern across the wider section of the duct. It adds tremendous stiffness and prevents (in almost all cases) the duct from doing the snap, crackle and pop from changes in temperature and internal air pressure.
Most of my rectangular ducts are inaccessable as they are in bulkheads. Some I may be able to access the tops only. Are there any ideas on how to minimize this situation or possibly fix it?
 
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