I recently read that insulated 6" flex duct has an equivalent duct length of two times it's actual length. And of course there's the issue of the pinching. So I was thinking I should replace this duct with rigid duct.
I have two questions. The first question is: am I wasting my time to do this? Can I expect to improve the air flow by switching 12' of flex duct to 12' of rigid duct and of course, eliminating any pinching?
The second question is: where can I find information about the proper way to install ducting? I have been unable to find any books or web sites that explain how to do this. Only thing I've managed to turn up so far is the claim that "duct mastic" is much better than any kind of tape and should be used to seal seams and joints. It seems like there might be a problem with fitting in the last piece of rigid duct. (Or is the ductwork flexible enough that I can bend it open to make room to fit in the last section?) This duct runs through an insulated floor. Rectangular ducting would be easier to fit in and insulate around if I can figure out how to install it and mate it to round duct ports at one or possibly both ends.