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Question on HVAC supply duct that needs to move

last month

We're in the planning stages of a major kitchen remodel and have found a HVAC supply duct for the 2nd floor which needs to be relocated. I've been told it cannot be located on an "outside wall" due to inefficiencies (heat loss in winter, cooling loss in summer). From a kitchen design standpoint it wants to be as close as possible to an outside wall while still meeting code.

My question is - how close can it be to an outside wall? What are the specifics (distance, insulation, air gap, drywall, etc.)? Any examples would be a bonus.

FYI - location code here for Michigan is to meet the the 2015 International Mechanical Code.

Featured Answer

mike_home

last month

It is going to require a custom solution.

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Comments (8)

mike_home
last month
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?
Eric Jackson
Original Author
last month
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.
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Sizing can be less of an issue when you have multiple units. Because each unit is controlled independently, provided of course the unit itself is not over sized for the area in which it serves resulting in excessive short cycling. In your case 3 ton plus 2 ton isn't necessarily equal to 5 tons of cooling... unless you drive those thermostats really low. By having two systems with total capacity of 5 tons (which, most of the time this would be oversized for a 1700 - 1800 sq ft structure) has a few advantages. 1. You have the ability to use one system only during low heat days or set the opposing unit higher. The unit set higher only runs if load conditions warrant.... meaning if it's not hot, the thermostat controlling the unit does not call... the unit can not run without a call... 2. Utility bills can be much less... because you rarely use both systems at the same time. You run the bedroom system when you sleep, the other when you're awake. If you have a home office in one the bedrooms you may need to rethink things a bit. 3. Extra capacity for when it's hot out. When it's hot you have the capacity to cool the home. (even while entertaining guests --- additional people add heat) Remember heat waves come, heat waves go... a so call 'properly sized' AC system is essentially properly sized roughly 10% of the time... especially if that system is a single speed AC system. Alot of people I come across like to sleep cool. So for that reason I doubt I would change the configuration of the space. Once you realize what you have, the choices you make are mostly budget type concerns. Essentially a set up like this runs like a 2 stage system. This kind of subject is above the pay grade of many... choose your contractor wisely. I service the Katy, Texas area.
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I had posted my plan a while back. Here is the part of the plan that shows the older space and the dropped ceiling area in the addition is the shaded. Currently, the HVAC guys propose one supply vent on each side of the fireplace and no ducts leading to the other side of the space. There are no soffits or closets in the older space. Those shadowed vertical bars you see on the right side are the exposed beams and they show how far the eaves extend. Thanks
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PRO
Charles Ross Homes
last month
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.
Eric Jackson
Original Author
last month
Thank you for this feedback. I think this helps clarify the comments I have heard.
mike_home
last month
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.
Eric Jackson thanked mike_home
PRO
Charles Ross Homes
last month
In a 3 1/2" stud cavity there simply isn't room for a reasonably sized duct insulated on all sides.
Eric Jackson thanked Charles Ross Homes
Eric Jackson
Original Author
last month
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.

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