Please tell me what I can do to keep the flexible air duct on the metal collar of my return. Return box is built of metal with a metal collar (the normal stuff used for HVAC). The collar faces downward into the crawl space approximately 3 foot to the ground. I cannot keep the flexible duct on the collar.:confused: :) :) :) HELP!!

You can put sheet metal screws to the wire in the flex duct or a large speed clamp will hold it.

Panduit straps would most likely work best. How big is the flex?

Once you tape the enter core of the duct and put metal strap around it with screws or duct ties using a tensioning tool and then pull the outer core over it and tape it the duct pipe will pull its self apart. My rule of thumb is not to ever use flex duct on a return air. No matter how well you instal it it will come apart again and again and again. Good luck.