Maybe I am overthinking this, but right now I have 12x2.25 register boxes in my floors (that are connected to 6" round duct). Now I am going to add the louvered wood registers on top of that. By my calculations the register box just barely supports enough air-flow for 6" round pipe-isn't the wood register going to choke things down considering it is not entirely open? Is this an issue? Should I go to a 4x10 box, 4x12? I'm not sure how much the standard louvered wood register box chokes things down but I emailed one guy who makes and sells them online and he says even the 4x12 size only has 20 sq. inchs of free flow area. Can anyone provide any advice about this? I see small louvered wood registers in a bunch of houses with 6" pipe yet by my calculations you would need a 6x14 register to actually flow as much through the register as you do through the pipe. Thanks for any advice you can give. Nick

im thinking about redoing all my ductwork in my attic, it leaks, is very dirty and basically (in my opinion) is not layed out right. i have sheetmetal ductwork right now and flex ducting would be alot easier to run. what is the downside to using flex tube ducting vs. metal ducting? and does anyone have picture or example of some ductwork that is layed out correctly? thanks.