# Adding new ductwork to a second floor.



## Marty S. (Oct 31, 2009)

You're not going to get all that in a 2x4 wall. Lets say you want 200 cfm in the big bedrooms,100 in the bathroom and 100 in the small bedroom. That's going to take a 8x16,at least, trunk to feed those 6-6" supplies. Going to also put return in the bedrooms?


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## vr4Legacy (Jan 25, 2011)

Thanks Marty, 

As for the trunk, you say 200cfm to each big room and 100 cfm to the small would take 6, 6" lines. Should I run two 6" lines to each large bedroom? If I need to run a large trunk, I suppose I can figure a way to run one. I plan on tearing out the plaster in my dining room and putting up drywall, so it won't be much extra work, I was just hoping to hide it in the wall.


As for the return I plan on leaving the gravity vents in all the rooms in hopes that will allow the cold air to return to the first floor. Also each door has at least a 1" gap on the bottom to allow air to flow under. If I do run a return directly from the rooms, what size should it be?

Thanks again for the advice.


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## Marty S. (Oct 31, 2009)

The 1" gap under the door will do. I'd run 2-6" on the big bedrooms and place the registers where they "wash" any exterior walls and windows. You can always close them up some if it's too much air which is a whole lot easier then adding more.


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## vr4Legacy (Jan 25, 2011)

Thanks again for the info. I'll work on figuring out how best to run a trunk to the attic. I think I have a place figured out. 

I may have some more questions as I get into the project. I'll post them if I have them. First project this weekend is to seal up the existing duct and insulate.


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