Saturday, September 19, 2015

Duct in a duct?

Hi,

I'm a the proud owner of a three story townhouse. The furnace and blower are in the garage at floor 1, the new room is on floor 3. This is a bit of an odd job because we're adding a room to already-existing construction. All the original ductwork is already in place. The challenge is that the new room needs a register, but there's no easy way short of punching a hole through the first and second floor ceilings to get a duct there.

The return intake duct (12"x12") is already there, and goes straight down to the garage from the third floor. What I am wondering is if I can route a duct (3.25" x 10") up through the return duct? I know physically that this is possible. What I am wondering is if
a) Is this is up to code, anywhere?
b) Has anyone ever seen this done?

I'm not so concerned about the flow rate through the return duct, as I only need 400cfm for the system. Assume I will insulate the new duct properly.

Thanks!

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