Originally Posted by paul52446m
It would help if you run 8" to the up stairs run. I would run the new hot air run in 8" and split it into too 6" up stairs, one to bath and one to main part. Run a 8"
return air and try to get the return hi if you can. Later paul
The only way to get any ducts upstairs is through a wall cavity so I think my choices are limited to an oval or rectangle duct for both the supply and return. I will do like you said and swap the 6" for the 8" for the existing duct to the second floor. Which is better, oval or rectangle? What is the biggest size that will fit in a wall cavity for each?