What is the rating and size of your AC unit? How long is the duct runs now? How long will they be when rerouted? Has anyone done a Manual J report/test?

Why do you want to remove the bulkhead?

For our kitchen reno to put larger cabinets there

@millworkman I don't have the answers to that at the moment. I don't think the J report test was done when we got our newer HVAC a few years ago, but we've been very comfortable with the results and it greatly improved flow into the two problem bedrooms since then.

To answer your question, the trunk duct can route vertical to attic, go across, then feed rooms down through the ceiling. The house I live in was originally designed that way. Manual D will determine the duct sizes for this distance and cfm. In any case, the ducts in the attic should be insulated, and it is always better to avoid flex duct for the branches. And if your supply for the 2nd floor is on the 1st, then I would assume you've addressed the return as well, not just how it gets down to the basement, but where it is in the rooms compared to the new ceiling supply locations. Also, not quite sure if you have a 2-story or 3-story house (basement doesn't count).

But other commenters make good points that should be considered. What is your kitchen layout, how many cabinets do you actually gain/increase height by removing the soffit?

I would leave the bulkhead and the ac and heating alone. Its working good, and cabinets to the ceiling are not all that useful anyway, unless you are all 6 ft tall or more.

Is your attic insulated? How will your attic ducts be insulated? And what will the exact location of the ceiling vents be? We had ceiling vents in one house, and I hated it. We lived in Las Vegas at the time, so we needed the AC to run full speed, but it meant getting blasted by the vent that was centered right over the bed. We ended up pushing the bed to a really awkward corner of the room to avoid that.

Heat from ceiling vents is even worse though. Because heat already rises. Your face feels flushed while your toes are still cold. Really don't recommend it.

What the mechanical contractor is proposing is a viable solution, but it's probably not the best nor least cost way to achieve your objective. It relocates duct work that is currently in conditioned space (per best practices) to an unconditioned attic space. It will also reduce the area on the 2nd floor to make room to run the duct. The best you can expect is that the modified system will perform the same as the existing system. My bet is that it will not, and you'll incur a lot of expense to implement the change.

As Debbi Washburn suggested, I would look at padding out the walls at the trunk line. The kitchen appears to be large. I don't think losing a couple of feet of cabinets will compromise the functionality. You may be able to incorporate some display niches in the thicker walls and make the entrances to the adjacent spaces more special.

Why not post a to scale floor plan of the kitchen and see what can be done without this costly and maybe bad decision. I did one home where we had to actaully put in a poratble AC for one room with a removal of ducting it was totally necessary but not ideal. It looks like you hva e a good sized kitchen space but the plan will tell us for sure .

Well, I thought we had another week or two to decide, but the crew showed up yesterday to do the work! I didn't have much time to think about it. They completed the re-route, and actually the air pressure in the 3 bedrooms seems pretty good (if not better) than before. It's not super hot here this week, so will check later in the week.

Also - we had our attic fully insulated a couple years ago in attempts to help with cooling in the master bedroom. They used flex lines in the attic and rigid metal for the trunk up. They placed it next to another line we had for the return so it didn't take up too much space in that room, maybe another 16 inches.

Appreciate all the feedback! I should have posted this a week ago! At least now we have high ceilings in the kitchen, and don't need to order new cabinets for that side. The cost actually wasn't too bad because we rolled it into another change order with some other things.

I attached pics of the removed bulkhead, and the line in my daughter's room. They have to still seal/frame it.

Ceiling vents are not ideal for heating.

IMPO

SR