Relocating Floor Duct to Wall Duct
HVAC ducting question from Ohio, zone 5A. We are relocating a floor baseboard defuser with a wall register in the same wall. The baseboard defuser is fed with a 2-1/4 x 14 x 5 (or 6) in. Galvanized Steel 90-Degree Round Register Boot. The wall is an interior, 2×6 wall.
We were going to replace it with a 10 in. x 3-1/4 in. to 5 (or 6) in. 90-Degree Stack Boot, create a small 3.25″ x 10″ stack duct and use a 3-1/4 in. x 10 in. Short Way 90 Degree Rectangular Elbow to feed a 10″x4″ wall register. The new wall register will be 6″ from the floor, quite close to the original baseboard defuser. It is a small bathroom and we are trying to get rid of this floor obstacle.
The attached PDF shows the parts we were planning on using (assuming its a 6″ duct – we will figure that out when we open the ceiling below).
Four questions.
(1) Are stack ducts allowed in code?
(2) The stack duct should not be in direct contact with drywall, right?
(3) Does code require that the stack duct be insulated?
(4) If so, what is the recommended way of insulating stack ducts such as this?
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Replies
I spoke with a local HVAC company owner who said that since it is an interior wall, the surrounding air is considered conditioned air (indirectly conditioned space) and therefore insulation is not required. However, because of the potential for condensation, it would be better to insulate. It doesn't have to be super thick, and the wall cavity wouldn't allow the traditional duct insulation. Possible options are Reflectix attached and sealed with UL181 tape (R 4.2 value is achieved through air sealing so complete sealing is required). That adds about 5/16" thickness. Another option is Frost King Self-Stick Foam/Foil Duct Insulation, which adds only 1/8" and R-3. It should also be sealed and wrapped with UL181 tape.
I don't think the ductwork is required to be insulated but if you are going to use it for cooling then I would definitely wrap it to prevent condensation. This is the relevant IRC code section: https://codes.iccsafe.org/content/IRC2021P1/chapter-16-duct-systems#IRC2021P1_Pt05_Ch16_SecM1601.
I don't design ductwork but I believe you should increase the size of your wall stack, to avoid potential whistling. You don't want the register to be the most restrictive part of the assembly.
Yes wall stacks are allowed by code. I have not heard of a requirement for ductwork to not touch drywall.