Mini-splits are an excellent solution for your needs but any mini-split system will require a hole through your wall.
The wall mounted, inside coil/fan unit must have pipes and wiring running outside through the wall to the condenser, which is usually on the ground below.
A mini-split system can be completely wall mounted, meaning the external condenser unit is mounted directly outside of the interior coil unit on the wall instead of on a pad on the ground but for a 3rd floor unit there is the problem of access.
- 'The MiniSplit Shop' carries roof and wall mounting brackets for a condenser.
- But the issue with a condenser wall mounted on a 3rd floor wall is the need for maintenance and your local building code in Cleveland may require access by someone standing on the ground.
So if you're considering a mini-split system for your 3rd floor, you need to be prepared for an external chase down the outside wall that houses the wiring and line set (two insulated copper pipes that carry the refrigerant).
- That said, though, the chase can be made decorative to match other trim on your house or even a downspout.
- We've even hidden a line set inside of a fake copper downspout on an historic house.
None of the other ideas - a small furnace in the attic, electric heat, or combined hydronic - can provide cooling to your 3rd floor, which is likely part of why you're considering a mini split system.
I suggest you work with an installer who is willing to make the outside chase blend in with the rest of your home.
For more information:
Read "I can't afford geothermal. Is an air-to-air heat pump my best option for heating?" a Q&A answered by Randy Potter.