Old 04-02-02, 12:20 PM
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I am installing AC/Heat Vents into a basement prior to drywall. I have to cut into the existing vent that supplies the rest of the house. My question is what connector do I use to secure the new ventpipes into the main air duct vents. I looked at the ventilation as it was installed originally and it doesn't look like anything but an elbow joint vent was used to direct the air into that vent. How is that elbow joint connected to the main air flow duct?
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Old 04-02-02, 01:17 PM
Join Date: Nov 2001
Location: USA
Posts: 1,873
What you're referring to is a coupling. When they designed your original system they fabricated the sheet metal into duct work and connections. What you want to do is add duct work to the original and it's going to be difficult to match the original duct work.

You can buy couplings at Home Depot and similar stores. They're usually round and are made for flexible ductwork. If you're using retangular ductwork, then you're going to have to go to a heating and Plumbing supply store and have one fabricated for you. They usually don't carry the retangular ones because flexible duct work is used most of the time in remodeling.

The way the coupling attaches to the main trunk is by the use of a multi-flange. You cut a prescribe hole in the main trunk and insert the coupling with these finger like flanges into it. Half of the number of flanges go inside the main duct and the other half out side the main duct. Then you stick inside the coupling and press the flanges against the duct. You do the same with your other hand at the same time to the flanges on the outside of the main trunk. By pressing the flanges against the main duct from both sides is what holds the coupling to the duct.

This is also where ducts are very leaky. I suggest you seal the joint with mastic. Just ask for it when you buy the coupling. There are other ways to attach couplings to ductwork, but they all work on the same principle, something clamps on both sides of the duct to hold the coupling in place. Also get a coupling with a damper inside it. It will allow you to balance the system if need be. And it's not that more expensive than one without one.

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