What you need to do is obtain an estimate for the cleaning of the air ducts in the rental and provide a copy of this to the landlord for his or her review with an accompanying letter stating the health concerns for having dirty air ducts separate and apart from the additional energy costs for heating and cooling the unit due to the current situaiton keeping a copy for yourself and wait to see the response.In the interim, carefully read the lease agreement in that its terms and conditions control the obligations owed you by the landlord and vice versa in the absence of conflicting state law. Look to see who has the responsibility of maintaining the unit. Most likely it is the landlord. If so, then you have some additional information to pressure the landlord to clean the ducts.Another option is to consult with a landlord tenant attorney about your situation.The last thing to do is have the health department inspect the unit's ducts. If the health department determines that the ducts are a health hazard, your landlord will be forced to get them cleaned.Good luck.