I just completed upgrading and re-configuring my DC duct work. I worked with the Blast Gate Company and they were great. They provided exceptionally quick replies to my emails regarding component sizes/lengths as well as design of the system. In the end, I chose to go with 5" Spiral Pipe for my main line with a combination of 4" and 5" takeoffs for my equipment. I ordered everything from them including the vinyl tape for sealing the joints. Today I finished up the install which was easy.
It isn't everyday you get to work with a company that understands customer service. Thank you, Blast Gate Company!