Hi Christine-

Typically, in attached late 19th / early 20th century NYC rowhouses, the bearing wall (the wall that is running parallel to the masonry party walls, usually near the stairs and directly above the cellar columns or arches) is actually a 'bounce' wall. It depends on the width of the house and how it was framed, but usually, the joists (the 'beams' running across the house) are actually supported on / pocketed into the masonry party walls and span the whole width of the house and the 'bearing / bounce' wall is there to keep them from deflecting or bouncing too much in the middle of the house. What that means is that it is sometimes possible to remove portions of the bearing wall by putting in a beam where the wall was as Anne points out above and it is sometimes possible to 'sister' the existing joists with other beams running in the same direction so that they can span the whole distance from brick to brick without any need for a bounce wall. This is a very long-winded explanation and every case is unique so I would recommend that you bring in a good architect who can in turn recommend a good contractor and good structural engineer to figure out what would work for you.

For your HVAC question, are you thinking about forced air heating and cooling? It is definitely done all the time in townhouses, it is sometimes difficult to find the best places for ductwork and equipment, but it can certainly be done.

I hope this helps you somewhat...