Originally, it had unvented gas heaters in several rooms of each apartment. Code required a retrofit to vented heaters, and really crummy through the wall units were put in, probably in the 60's or 70's. They're all at one end of the long, narrow apartments. At the back of the building, there are service porches for each unit, where the water heaters live. There's about 2 x 3 feet available in each service porch to put some sort of HVAC gear. The electric sub panels are also there.
What kind of central heating would be reasonable to install? Would an upgrade to both heat and A/C be a good idea?