Converting Landlord Paid Heat Equipment to Separate Metered

[Chris R.]

We bought a three family multi this summer in NH that was previously owner occupied for many years. The last owner provided the tenants hot water radiator heat via a single thermostat for the building that he controlled in his unit.  That being said, we just installed a thermostat that limits the heat to 72 F on the top end because it was like Hawaii when we came up to work on the vacant unit and its costing us a fortune.  We intend on buying new separate-metered equipment so each unit can control their own.   

The burner is oil fed, dirty, and expensive to run under tenant control (as expected).  There's a NG line that runs by the house that we could tap into so we'd like to pick your brain about options that worked for you if you had to deal with this.   Separate wall vented forced air NG units? New small boilers in the basement that feed existing plumbing loops/radiators in each apartment?  What did you spend?  Would you do anything different?

Thanks, Chris