Lockport, IL -What is annual estimate for an 800ft unit's natural gas bill for heat?

[Gustavo Dominguez]

I am looking at a multi-family property in Lockport, IL. It is a 4 unit (three- 1b/1b & one studio). They pay their own electric and water is well (unincorporated area). Heating would be paid for by myself. The landlord said he pays about $175 for all units per month on average, but I'm not so sure he's being totally honest. If anyone has rentals out there can you please let me know what you pay for heat? Thank you in advance!