Accounting for Chicago Heating Expenses

[Ben Wilson]

I'm looking to purchase and live in a small multi-unit property in Chicago, and I would be interested in gaining some input on how to estimate and account for the expense of heating in the winter.  Obviously this will vary depending upon the property, but are there some general guidelines for how to anticipate this expense in the event that I am unable to obtain the information directly from the seller?  

Having only lived as a tenant in Chicago for 1 year, I don't know what heating costs, but I'd imagine it isn't cheap.  I've noticed that many landlords include the cost of heating in the monthly rent - I'm guessing because all units are heated from a single source.  Experienced Chicago investors, what do you do?