I don't think there is a code which states a supply duct cannot be within an outside wall. I will defer to the code expert on this one.

If it is allowed, then it becomes more of heat loss and gain issue. Are you able to build a chase on the exterior wall so it states inside the conditioned envelope?

Thanks Mike, That would be a no on the chase, I don't want to get into modifying the exterior. There are interior options that exist, but they do take away from the overall appearance of the kitchen layout.

FYI - I have had conflicting information on whether this is a code violation or just a "not preferred" due to efficiency losses.

Best practice is to not install HVAC ducts or plumbing in exterior walls. I don't think the 2018 IRC prohibits installation of ducts in exterior walls provided they are insulated to code required R-values. If you are not able to do that, your cabinetmaker may be able to leave a void space at the rear of cabinets to accommodate the duct work.

Thank you for this feedback. I think this helps clarify the comments I have heard.

It is common in many parts of the US to install duct work in the attic. Attic temperatures can reach 0ver 125 degrees in the summer, and below 40 degrees in the winter. This is a bigger temperature swing than you would see in a exterior wall cavity. The duct work used in attics usually has a R6 or R8 rating. You should be fine if you can install an similar amount of insulation between the duct and the exterior wall for a short run.

In a 3 1/2" stud cavity there simply isn't room for a reasonably sized duct insulated on all sides.

Thanks all who commented. The exterior walls are 2x4 construction, so as mentioned above, with insulation, there’s no room left for a duct in exterior wall.

I’m going to work with a cabinet supply designer on a couple of options to hide the duct within the cabinetsbinders.