Want to convert apartments

[kimana]

I have recently upgraded my 3 unit apartment building w/new windows,doors and insulation.Currently,the units are oil fired hot water baseboard.Each unit is on its own circulator and t-stat.I pay the oil.The boiler is 25+ years old and we are looking at retirement soon.We would like to install separate units that would utilize the baseboards either in one central location(utility room as now) or in each 3'x5' closet on the 1st floor.The idea is to have each tennant pay it's own fuel bill either electric or propane.
I need some ideas what you would recommend.
Thanks
Jeff in Pa

[Some Dude]

There are so many options to chose from.
I will say to remember there i a 1.80 per square foot tax incentive on upgraded commercial work if you can Increase eff by 50 %