noises in ductwork

[jvtran04]

I have a house 7 months old. We started using the furnace around November of 2004 when the weather got colder (this is when problems started happening). The problem is when the furnace would turn off after a complete heating cycle, we start to hear loud ticking noises from the ductwork and once in a while after the furnace has already been off for 10-15 minutes, the main rectangular duct run would give a load bang noise.

I think I know what the problem is, the duct work expands when it heats up and when the furnace turn off the ductwork cools off and contracts therefore making the noise.

The HVAC Company that installed the system has come out 6 times and cannot get rid of the noises. This same company installed a complete system in another one of my new house and there were no noise problems. The company blames the issue on the fact that by code now they are required to put screws in where the duct work joins together. In doing so, the ductwork can not expand and contract properly.

So far they have:
• Installed an addition cold air return vent on the furnace itself hoping to get more air in the system during the furnace cool off stage.
• Adjusted the ductwork to make sure it is not resting on any i-beams
• Installed proper strapping to make sure the round ductwork is suspended inside the floor joists and not touching any wood.

I am about to give up as I don’t think they will ever be able to resolve this issue, BUT I can’t give up because I am in the process of finishing my basement and will be at the drywall stage soon. Needled to say, if I start dry walling the ceiling and the noises are still there, I will go Crazy…

Please help. Thanks!

-James

[HayZee518]

The noises are the joints expanding and contracting. The loud bang is a trunk line that isn't cross creased along it's length. When it heats up it expands and cool down contracts the sides. Have the hvac co install strapping in the middle of each trucnk section fastened to the joist. To the duct - 1/2" sheet metal screws.

[imeduc]

Like said if the duct was not cross broke it will bang when the blower comes on and off some times. Some times a T slip screwed to the bottom of the duct can stop it . there also is a flex joint that they can put from the furnace to the duct that work sometimes.

ED

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