Boiler Gas Bills out of control

[Roseann Koefoed]

I’m under contract on a 6-unit building in Chicago’s south side.  I like everything about it, minus the gas bills.  In recent winter months, $1200/month.  Averaging $9,600 for the year.

I don’t know the boiler brand / energy efficiency (yet), but I’m told it’s about 10 years old.  

Have any of you had luck battling Chicago’s increasing gas bills by either buying a new, more energy-efficient boiler or changing the heat system entirely?  Or changing the gas-powered hot water heater to an electric water heater?

The apartments are all updated and look great, so I would not be interested in gutting the walls and trying to install a forced heat system.  I own other similarly sized buildings on the south side, but the heat is separated / forced air in those.  So this would be my first experience with a boiler in Chicago.

Appreciate any advice!