A. Before getting to layout and ceiling height, the first question you should ask has more to do with the building than the apartment--i.e., whether the co-op or condo board has ever approved central a/c before.

A board that's gone down this approvals road before "is less likely to react against such a proposal," says property manager Thomas Usztoke.

He notes that boards tend to be most amenable to central a/c systems that are installed completely within the apartment versus systems that rely on exterior mounted components, like a condenser on the roof. (See The big chill: Putting central air in a prewar apartment.)

Instead, through-wall condensers are typically mounted below a window facing an airshaft, or sometimes in the upper portion of the window itself, if the view isn't a treasured one, says architect Thomas Degnan.

"In general, look for apartments with high ceilings and an interior light well access [airshaft] where potentially a wall-thru a/c condenser can be installed," says Degnan.

An upgraded electrical system is a plus too. Otherwise, new power will need to be run from the basement, which gets pricier the higher you go.