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Old 09-30-2011, 06:53 PM   #1
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Supply ducts to second floor

I purchased an old farmhouse that has no heat to the second floor, gas forced air to the first. The heating system is new and has a 26 x 10 ductboard trunkline running under and perpendicular to the joists in the basement, flex duct to first floor registers. The heating contractor who installed it assures me the system was installed with the capacity to take on the second floor.

I would like to consider doing this myself. I've got fairly extensive remodelly experience and feel up to the challenge but must admit I have never done anything in HVAC save for adding a takeoff and flex duct to an existing system.

My question posed to smarter folks than myself is can I build a vertical run off a main trunk to a distribution box and then run three round branch ducts off of it? More details follow.

At first glance I thought it would be fairly easy to run flex or round metal supply air duct to the second floor because, during the course of the renovation, I've removed the first floor ceilings, providing access to the joists under the second floor. However, it has become apparent that the only reasonable access from the basement to those joists is through a closet where I can garner about 21" x 7" of useable duct space.

I have access to a ductboard cutting machine and am wondering if I can construct a branch line such that it would connect to the top of the trunk, travel approximately 2 feet between the basement joists to a point where it would turn vertical and move up the closet space to a larger dead space at the top of the closet. I would then run three duct lines off a distribution box at the top of this branch to the rooms on the second floor. They are two small rooms (7" round) and a small bath (6" round).

Would this approach work? I don't have any alternative clear paths to the second floor except for this 21 x 7 inch closet space. Many thanks!


Last edited by cekrauss; 09-30-2011 at 06:56 PM.
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Old 09-30-2011, 07:39 PM   #2
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Won't get much air through a duct board trunk that is ran in between the joist. Unless you made it 10" deep. Also, the 26X10 trunk you would be connecting to would need to be made bigger, so as not to rob air from the first floor. Probably about 10X30. I'm guessing your giving outside dimensions, and that your duct board is 1" thick, that what I based my sizing on.


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