opening existing air ducts

Im finishing my basement and there are air ducts already on the ceiling leading up to the house. I would like to know how to open them to get air flow in the basement?

 

You can buy simple saddles to put on these pipes, but I'd advise against it. To get good air flow and to avoid excessive noise transmission between the floors, you should install separate takeoffs and pipes for your basement.

 

I also am finishing my basement and encountered the same problem. I also wanted to continue doing it myself. One consideration passed on to me (I am by no means an expert) is to find out wheher your system can handle the increased demand. I opted for the "go for it" method and cut into the main trunk line but added butterfly valves to make sure I would be able to control how much was being siphoned or taken from the main line and elsewhere in the house.

If you are adding a drop ceiling the running of new "lines" will be much easier and offer more options. I originally was planning to run new trunks to the outside walls and then down. A drop ceiling made my life easier.

Do not forget to add returns so that there is a balance. And finally, for what all of this is worth, it may be worhtwhile to hire an HVAC expert solely to come in and make a few suggestions that you could later follow.

Good Luck.