mini splits to supplement existing HVAC in old house?
Our house was built in 1905 and has balloon framing. When we moved in eight years ago, we replaced the old forced hot air furnace with a Carrier Infinity system that gives both heat and A/C. We used the existing ductwork (absolutely no idea when it was installed or how well it was installed), and I do not believe that there is a return on the second floor. The system does a very good job heating and cooling the first floor, but it's far less effective heating/cooling the second floor bedrooms.
We are now looking for the least invasive way to improve the heating and cooling in the three second floor bedrooms and the third floor attic bedroom. We really, really do not want to rip open walls to mess with the existing ducting or to add a second floor return.
We considered a high velocity mini duct system like Spacepak or Unico, but I think that only provides A/C and does not provide heat, right? Would a mini split system with 4 inside units be a good solution for us? I'm not thrilled about the look of the mini split units on the walls, but I guess I could live with that. Do they do a pretty good job at both heating and cooling? I've read conflicting information about how quiet they are. Does anyone know if the lines to the outside compressor and for drainage can be run inside our balloon framed walls rather than on the exterior of the house? (The walls do not have insulation and we've been able to easily run electrical and cable in them.) Is there another minimally-invasive solution that we should be considering? We're in Maryland, by the way.
Thanks in advance for any insights you can provide.