Options for new heating systems in a Tri flex

[David K.]

I've noticed a lot of Tri-plex (3 family) houses have one central heating system I've looked at lately.  Other units have these old fashion "gas stove" type systems in the northeast.  What other options would I have to make each unit independent?  Would like to house the additional units in the basement, electric baseboard wouldn't really work for a decent sized 2 bedroom unit.