My NYC co-op is going through this now. All of your guesses are basically right. We're having separate systems installed for replacing in-unit hot water and in-

My NYC co-op is going through this now. All of your guesses are basically right. We're having separate systems installed for replacing in-unit hot water and in-unit heating and cooling. I believe the new electric hot water system is being installed in the basement and the condensers for the in-unit control panels are being installed on the roof and routed through the pipes used by our old radiator system. Pros: units can control their own heat and will no longer need in-window A/C units. Cons: it's really expensive, even for a building with good finances and access to reasonable financing options. We're only doing this because our boiler is probably a few years away from failing already (it's well over 50 years old), and we're super close to the building size threshold where we would be fined for not complying with the law (so any adjustments to how they calculate building size or dropping the law's fine floor would certainly push us over).