I am adding an addition to my house in the DC area. it is 18X16 with a 9 foot ceiling over a crawlspace.
In a previous renovation to my house on the second floor, a second plant was added to handle HVAC for for the second floor and the lines that ran to the 2nd floor (2 lines, yes it was cold in the winter) were capped off.
My plan for the new space is to take one of the capped off 4X10 ducts, switch it to a 6 inch round flex line that will run 12 feet under the crawlspace, then split it into two 4inch flex lines that will run to wall vents on the "sides" of the room. On the far side of the room I will put a return hooked to a 4 inch flex that I plan to attach directly to the return stack of the furnace.
I'm wondering if this seems reasonable and if anyone has anything they see that may be an issue.
Thanks for any help!