We have two mini splits (kitchen area and master suite) in addition to window units in other bedrooms. Luckily the main living areas keep cool enough with ceiling fans. The splits are not particularly attractive but do the job. We have had some issues with them but I blame the install as the units themselves (Fujitsu) get good reviews. We also have a pioneer model in our carriage house we like that was installed by someone else and no issues. House was built in 1853.

Please take a look at the Unico high velocity duct system for central heating. They have been using the system for many years on This Old House to deliver comfort in tight spaces. Mini split units have some options for remote ducting as well. I have, in the past, done multiple units. One attic unit to service the second floor and one basement or crawlspace unit to service the first floor. Hiding ducting meant window seats and lots of effort, but the lower cost of the high efficiency furnace and air conditioner made it pay pack in a few years. Took the opportunity to insulate like crazy at that time!

Great question! We're about to move into a circa 1900s place and need and AC fix since we face the same issues.

I just hated to think about what might be done to our original oak floors, and the walls are lathe and plaster. I don't know if individual room units would ruin the look of the walls, but they have to look better than window units.
We have redone electric so that's not an issue. And, at least for us, funds are by no means unlimited, so we have to consider the economics of whatever we do.
Frustrated!

Making an omelette requires breaking some eggs... But...any existing registers can be left in place. If you currently have steam radiators, new ducts and floor registers can be added with minimal damage if accessible from below. Unico vents are 4" round covers. They require a 4" diameter hole in the ceiling. We have hole saws that cut the lathe and plaster cleanly for that. Access from the top must be available. Register covers in historic styles are available from Reggio or Steelcase...even for those Unico vents. No collateral damage at all? You are stuck with window units for AC. How was the house rewired without damage to plaster walls and ceilings?

Yes,you are right, Ironwood. We had to go into the walls for the work on the electric, and honestly, in some places, the replaced wall actually looked better.
We have radiator heat--no vents anywhere.
How does the system you describe compare cost-wise to the ductless system?
The one company which gave us a quote said $26,000. We haven't gotten another estimate, because for us, that is a lot.
That's why I thought I'd check here on Houzz for advice.

$26K? That's astronomical even for the SF Bay Area! I've had the Unico system quoted for less than half that for a 2400 s.f. home. I just did a standard full duct replacement with a high efficiency furnace and new AC unit for a main level with a new mini-split heat pump system (ducted) for the second floor for under $15K. We had a lot of tight access and finished areas to deal with too. We used all custom Steelcase cast aluminum vent covers...that added about $900. Maybe look for a second opinion?

Our house is just under 4,000 sq ft. Even at that, we thought that price was pretty high. Budgeted $12K which is about all we can do. I was discouraged after we talked to the guy.
I feel really ignorant about this type of thing--I am the DIY queen, but not with anything mechanical.
Really appreciate the input! Guess it is time to get a second opinion now that I have a ballpark figure...

Just an update--whole house done w/ductless system. Love how quiet it is! Not that good looking, but efficient for our purposes! Best part-under $10,000!
Thanks--Esp to Ironwood.

So glad it worked out! I thought ductless mini-splits would be the cheaper option. I also have a historic home. But I just got an estimate for installation of 7 units and am gasping at the price: $39k! I know I live in NYC, but that's high, right?

I'm having a unico person for an estimate next week. We'll see which is cheaper.

Ephillips-$39k is high! We got 5 units installed for about $10k

Hmm. When I googled the model numbers of the Mitsubishi units, the equipment alone was 10k. Your labor must have been very cheap. But 30k in labor is over the top in any market I think.

Our equipment was about $6000. Our units are Carrier. The system literally cut our summer cooling bill in half. We will see how we do this winter.

We see this issue here in the Philadelphia market often. One good and flexible solution is a mitsubishi ductless HVAC system. One of the surprise benefits is these units do heat as well. Big cost saver in the spring and fall. They will keep you from firing up the whole house heater for a couple of weeks.

@Generation 3--- How much for equipment and installation for one of those in your city?

That is a really good question. I'm looking for a way to communicate the answers in a way the accounts for all the different variables. A rule of thumb could be to expect to pay between $900 & $1400 a room.

I'm still collecting information to better understand the market. It is changing rapidly.

Just to clarify on my $40,000 quote in NYC: The price was for 7 units. Instead of the simple install of mounting on an outside wall, they were internal with the exhaust feeding up through the center bathroom vents to the roof (through 3 floors). A crane had to be rented to lift the two outside units to the roof where they were going to mount on the side of the chimney. Extensive electrical work was needed to connect the units to a power source. And the quote included patching and painting to cover the work. They suggested it would take 3-4 workers about two weeks.

I think this is affordable when you are doing one or two room and it is mounted on an external wall and can feed right outside without a complicated set up. For me, given the price and the bulky (ugly) look, I'd rather spend the money on true central air. Amazingly, I got a quote for a Unico system (central air for difficult spaces/much more attractive) and it was $41,000. Obviously, for the money, this seems like the better choice for me.

So, what's the verdict on "plaster walls" for mini-splits?" Is it possible?

Can they find the studs?