Section 6-501.14 - Cleaning Ventilation Systems, Nuisance and Discharge Prohibition(A) Intake and exhaust air ducts shall be cleaned and filters changed so they are not a source of contamination by dust, dirt, and other materials.(B) If vented to the outside, ventilation systems may not create a public health HAZARD or nuisance or unLAWFUL discharge.Wis. Admin. Code Department of Health Services § 6-501.14