# Ductwork Expansion/Contraction



## gowings (Nov 10, 2013)

Every time my furnace kicks in the duct work right above the furnace thumps. Its the duct work expanding with the heat kicking in. I was told to drill a 1/2" hole in the side ducting of the heat side as it leaves the furnace to relieve some pressure. That didn't help. Any ideas how to stop this. I'm all ears. I have A/C also, so there is a A coil present. Yet my other houses had the same setups and no issues.


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## Tom M (Jan 3, 2007)

Get a canvas transition duct


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## flashheatingand (May 3, 2008)

Was the plenum cross braked?


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## beenthere (Mar 5, 2009)

flashheatingand said:


> Was the plenum cross braked?


May not have been cross broke. Or may have been made from too thin of a gauge. 

Pics would help.


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## flashheatingand (May 3, 2008)

We forgot to mention the possibility of an extremely high static pressure as well.


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## gowings (Nov 10, 2013)

what is high static pressure caused by


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## Tom M (Jan 3, 2007)

Its the initial force of the blower when its turn on. The braking these guys are saying is nothing more than putting a crease in the flat sections of the dust to take the pop out of the duct..it strengthens it. I also believe a canvas transition helps prevent an echo of startup noise.


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## gowings (Nov 10, 2013)

So since I can push the side duct in and out. Is that where I would put a cross brace on
Here is the pics


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## TXACguy (Jan 12, 2014)

*Put on some braces*

If you don't have a good tin man, you can go to lowe's or Home Depot and get a piece of angle, galvanized. Then get some self tapping screws and run the angle cross-wise on the side of the duct. do all three sides if you wish. It may be just one side causing the noise. If you can push the side if the duct in, you probably are working on the right deal.

The aforementioned flex joint is an alright idea as, well as the bracing. But remember, you have to insulate it and cut your plenum. So me thinks the cross braces are much easier and you can fix it in 15 minutes with the braces. Hope that helps...


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## gowings (Nov 10, 2013)

Thanks for your help. On my way to HD:thumbup:
Now onto my next headache, laying pex on a 2200sq ft.styrofoam basement floor


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## beenthere (Mar 5, 2009)

The sides of the plenum or cross broke.


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