DC transition fitting?

[Jay Yoder]

I am working on the DC for my Miter station and was thinking of running rectangular duct under the "bottom" of the cabinets. I found a 3.25x10 to 6" rd transition at lowes and it got me thinking about the rectangle option. Would this fitting work? I would hate to design the system based on it only to find out that it slows flow down too much.

http://www.lowes.com/lowes/lkn?actio...411&lpage=none

see attachment for cabinet...

[Tom Veatch]

A square/rectangular duct will offer more flow resistance than a circular duct of the same area. To get a ball park comparison, take the square root of the width times the height of the rectangular duct. The result is the diameter of an "equivalent" round duct. That's not an exact comparison, but it'll give you a ball park idea of how they relate.

For example, you can expect a 3.25 x 10 rectangular duct to be the equivalent or maybe a little better than a sqrt(3.25 x 10) = 5.7" diameter duct.

[Ben Franz]

The 3.25 x 10 x 6 straight fitting is usually called a fan boot and is used to hook up smaller vent fans or microwave/vent units over a range. I think it would work well in your application. The drawing you attached looks like you're planning to use a transition that has a right angle built in. This is, oddly enough, called a right angle register boot and I think the right angle bend in the rectangular section will cause a fair amount of turbulence but still outperform a 4 inch reducer. I'm using 4 x 12 x 6 right angle boots to make floor sweeps.

[Paul Demetropoulos]

[quote=Tom Veatch; For example, you can expect a 3.25 x 10 rectangular duct to be the equivalent or maybe a little better than a sqrt(3.25 x 10) = 5.7" diameter duct.[/quote]

Which is about what it transitions to, a 6 inch round. Should work fine.

[Jay Yoder]

Using this adapter at both ends would be the rough equivalent of 6" the entire way along. I was thinking of running the rectangular duct under entire length of the station, with an auxillary connection on the LHS,the miter saw connections in the middle and the outlet on the RHS. This would allow me to use the adjustable plastic legs to level it to my concrete floor and build the cabinets as typical (although deep) cabinets. does this setup sound plausible?