My grandfather had a vertical PTAC back in the late 1950's early 1960's. It was a small unit only heating/cooling a single room addition to the house. He apparently chose that because the new room could not be ducted into the central system due to the way it was constructed (ducts were in crawl space, but the added room replaced a car port and had no crawl space). This unit was vertical, and from the best of my memory was about 18 inches wide, 5 to 6 feet high, and protruded from the wall about 6 inches or so. It vented to the outside via an external vent located at the bottom of the unit through the wall. The outside vent was slightly higher than its width, maybe 18 x 24 inches. It protruded maybe about 1 inch from the outside wall. The inside had 2 vents, one on top (output) and one on the bottom (input). So the air traveled up through the unit when the fan was blowing. It also had an external thermostat which had been installed on a different wall 90 degrees so it was not in the direct airflow.
What I am looking for is a split version of this so I can mount it on interior walls. I'm looking for single room capacity, not whole house. So I would presume the very same condensers used for mini-splits would work with this. Basically this would be a mini-split, with heat, but designed into a vertical form factor.
All the mini-splits I have seen are designed into a horizontal form factor. That won't fit in all the places I want to do this.
I have seen some VTACs, but these units appear to be intended for larger service (e.g. all rooms of an apartment unit), and are designed for hiding inside a closet, and apparently to be connected to some ducting. These appear to be central units with a small floor footprint. They are definitely not intended for embedding in, or mounting on the surface of, a wall.
My options do include embedding part of the unit in the wall. With my current floor plan, there will not be any places where a unit would be back-to-back with another unit, or with any electricals or plumbing. The width should not exceed 20 inches. The height should be at least 60 inches but not exceed 80 inches.
I'm concerned that no manufacturer has considered the width issues with mini-splits, and thus only makes mini-splits in the wide short form factor. If there are no such units available in a vertical form factor, I may have to completely re-do this house floor plan and design.
Please don't suggest a zoned central system. I've ruled out a central system a long time ago.