Basement: Why cut a hole at the top of main duct?

[letitbe]

I was advised to tap into the main ducts top, to add an extra vent in the finished basement. However it looks like it's extremely hard to do - the duct hangs just below the basement ceiling, so I would have to take it off the hooks, and also lower it for the extention duct to go at the top to the outside wall. Can I make a hole on the side, or on the bottom of the duct?

[Jay11J]

If it's really hard to tap on the top. then go ahead and do it on the side.. You'll just have to build a bigger box around this if you are planning on finsh the room.

[letitbe]

Thank you very much! I will try it!

[Ed Imeduc]

Do it all the time. Just get a left and right aviation snips and you have it made. use a square take off for it . Cut the hole . The 6" take off will fit right up there on top of the duct in the joist. Put the take off in it and bend the tabs over is all. If you come out the side then you have to go up to get in the joist line so that means another L90o just more drag on the run

ED ;)