Separating utilities and installing HVAC

[Todd Riedel]

The property I just bought is not metered separately and has one giant old furnace. I would like to separate the utilities so the tenants can start paying their own also the city is requiring each unit have its own heat source. I’ve been debating between putting in new furnaces, running baseboard heating, or installing wall mounted heating and cooling units. 
   Do any of you more experienced landlords know what the most cost efficient rout would be here?