Interesting question. If we had a completely empty apartment some level of dirt would get inside over time, presumably some through the chimney. And if the lease requires returning the apartment to the original condition, that could involve some fire place cleaning (in theory). Does the lease explicitly exempt "normal wear and tear".

Past that, the previous answer was a lot more specific. And it would be interesting to see how a small claims court would call the chimney issue. The contract can make you responsible for ending Global Warning in the small print, but Small Claims Court tend to use Common Law standards where your argument would likely have more traction.