and how many BTUs do you think? Also, any favorite brands? --65.185.xx.xx

You need to do a manual J calculation to determine the BTU based on insulation and glass load along with other factors, when the manual D calculation is within 10 percent for the turnover rate and you use the existing gas furnace as the BTU. You often find someone used double the BTU value and it works but short cycles leaving cold spots, I have used Samsung and Mitsubishi because they have units that work when it is -10 outside, the cheap units work down to +25 so you will be using the baseboards again. --76.190.xxx.xxx

There are two parts to installing a HVAC system which are the heat loss and heat gain. More then likely the structure is poorly insulated where it is like a bucket with hole where have to make that hole smaller so less water is required. Spary foam is the best insulation where no air infiltration. Upgrading windows to low E with argon gas will decrease heat loss and heat gain. Best option is to with a high efficiency mini split where it is better to install a larger unit as a high efficiency mini split works on the modulaton principal where the compressor works at a varible rate where under low demand the compressor will not run at full capacity. Most will require 240 VAC with 15 to 20 amps. There are parts to insulation which are rough in then connecting all fitting along with hard wiring outside compressor along with a stand or concrete pad. If want to know more about insulation of high efficiency mini split then view many videos on You Tube. High efficiency units use the least amount of current or power where look at a SEER 22 above. Also look at insulation. --68.69.xxx.xxx

Talk to someone who installs minisplits daily. We have two, one in each of our garages, we installed one and one we paid to have installed. Maybe there is a reason your building would be difficult for install, but I didn't think so, we also had plenty of electrical power in these buildings so we didn't have to upgrade the electric panel. Talk to a few other installers and soon you'll know if it's feasible. We love our, easy to use, heat and cool, inexpensive to operate. --172.56.xx.xx

So we use through-wall heat pumps instead on all our other cottages because they are much cheaper than mini-splits for US, and economical for the tenants as well compared to baseboards. We leave the baseboard as back-up, but no one uses it. --50.82.xxx.xxx

Oh and just finished an ADU with no source of HVAC except for two of these through-wall units, and it passed Certificate of Occupancy compliance for that with no problem. Our electrician had already told us that as long as a unit just plugs in (as these do, 220 volt) it requires no inspection and no permit. A mini-split requires both. --50.82.xxx.xxx

Makes sense the through wall cost less than the mini split. With a mini split, you need to support the indoor and outdoor units, make a hole through the wall and connect the indoor and outdoor units, then charge the units. With the through wall, the connections and line charging between "indoor" and "outdoor" units are already done at the factory and the hole thorough the wall provides the support for everything. I guess the mini split has the advantage of a small 3" diameter hole vs the 20 x 40" or so cut-out for the through wall. --74.102.xx.xx

Makes sense the through wall cost less than the mini split. With a mini split, you need to support the indoor and outdoor units, make a hole through the wall and connect the indoor and outdoor units, then charge the units. With the through wall, the connections and line charging between "indoor" and "outdoor" units are already done at the factory and the hole thorough the wall provides the support for everything. I guess the mini split has the advantage of a small 3" diameter hole vs the 20 x 40" or so cut-out for the through wall. --74.102.xx.xx

Mostly though we just toss them if they die. --50.82.xxx.xxx

I have MItsubishi for AC and I think itwould produce heat also but I have lovely radiators and a Burnham in the basement.It's 18 K for AC and cost six grand so it better have heat also. Yes small hole but I have to cover it in plastic because cold air comes in like a reverse blowtorch. I have a Fujitsu and one of the rentals for AC. It has been very reliable. --71.188.xx.xxx

--74.102.xx.xx

I personally installed a 9,000 btu mini split last summer in my converted garage. Wasn’t a difficult job, as I had watched several videos first. Pulled a good vacuum and it is a quiet highly effective unit. I wish I could put them in all the rentals. However, the stigma of several units around the houses may be a turn off for tenants. My average rents are about $1650 a month. --47.32.xxx.xxx

A PTAC is never as efficient as a high efficiency split pump. On Amazon can buy complete high efficiency split pump. If a larger split pump is used then the heat pump will reduce compressor speed to compansate for less demand. it is better to go with one size up then using a smaller unit. The other important feature is to buy a high efficiency heat pump that operates when it cold out without using heat strips. --68.69.xxx.xxx

It sounds as if this switch is an effort to save money, if this is the case, consider all of the hours , days and weeks that the new unit won’t be in operation. Next consider that during the coldest weather in the mid west, the heat pump is overridden by the back up electric heat strip. Weigh these considerations against the cash outlay and the payback is far into the future. --149.76.xxx.x

We don't like through-window because the air leaks like a sieve through the open window - you have to come up with all kinds of way to insulate around it. Plus it blocks the window and some of our cottages only have one window in the bedroom. Blocks emergency egress. And it just LOOKS worse hanging out the window both inside and out. --50.82.xxx.xxx

--74.102.xx.xx

And two, for DH's purposes, much easier to replace the unit over time. Pull the old one out, slide the new one in and done. No futzing about with re-insulating the edges or worry about damaging windows, etc. --50.82.xxx.xxx

--70.92.xx.xx

We have a few of the Amana PBH093G35CC 9ks out there which do require a separate sleeve - they work for thicker walls (we have two of these in a brick cottage that required some WORK to get the holes cut!) --50.82.xxx.xxx

He thinks it took us awhile to figure out what worked where. --50.82.xxx.xxx

With rentals every dollar spent have to get that back where a few months of vacancies will exceed the cost of improving energy consumption. Even improving existing equipment by adding pipe insulation then turning off a loop that is constantly running reduced wear and tear where fan coils lasted longer. In order to charge a higher rent have to show value for that. In the house considering adding high efficiency mini split heat pump where house has no Ac where it is warm in afternoon then cools off at night as a steel roof does not absorb as much heat as asphalt shingle roof. With higher energy costs in the future then using minimal efficiency equipement is less viable. Having a additional heating system where there is high efficiency wood stove along with another system where can heat one room then the other rooms at a lower temperature. --68.69.xxx.xxx

Would you assume on average...1 per each BR and 1 for Kitchen/LR....3 total? --70.92.xx.xx

If using a mini split then can have one compressor outside then have 3 devices on the wall for heating and coolng in the house at three different locations The compressor can be mounted on a stand higher up So the cost of 3 PTAC or one mini split with 3 wall monted cooling and heating devices. --68.69.xxx.xxx

We do have a few that are under-window just because that's the only wall-space that worked. --50.82.xxx.xxx

Thanks again WMH, for sharing the details of your solutions and the context they were applied. Very helpful! I was going to ask, "why through-wall for the bedrooms ACs?", but then I remembered your previous explanation on that. Let me know if you ever need that sleeve :-) --74.102.xx.xx