Renew Gas Boiler or Install Mini-splits to 5 unit house

[Hoi L.]

Need some collective advice/recommendations.  Appreciate any and all help!

Closed on 5 unit house with efficiency/1BR (7 occupants) last week.  Currently all units are ~$50-75 below market in the zip code with water, hot water, gas heat/cooking included.

Monthly gas is ~$300/month year round (higher in Winter of course, etc) and the current gas boiler/heater is 20 years old and the longest tenured tenant told me that it was on recently after a circuit breaker trip and it had to be turned off manually at the unit.  So, I am thinking the boiler is nearing the end of its life.

Should I replace the gas boiler vs installing mini-splits in all units since the utility costs would go back to the tenants (they pay electricity) and I may be able to charge more since the units would have AC too in addition to heat (Philly is no longer that cold in the winter).

If ROI is within 5 years, then I am thinking to do it.

Any suggestions?

Thanks!