rerunning ductwork

brent07

i'm remodeling my basement and i'm trying to rerun my ductwork as close to the support beam that runs in the middle if my basement. Existing there now is a traditional trunkline with cutouts that 6' duct runs off of. im switching to 6' insulated flexible duct, my real concern is the trunkline. my furnace is behind a framed portion in basement and the trunkline runs out from that; would airflow and all of that work correctly if i built a box from sheet metal that would be compairable in total size of existing trunkline but it would be a box behind the framed portion with the cutouts come from that? so instead of the long rectangle that is there now that runs about 5ft, it would be a square box. hopefully that makes sense, thanks

beenthere

A pic of what is there now, and a drawing of what you want to do would help.

Changing from 6" metal to 6" flex will reduce air flow.