The answer to 'ductwork smells bad' is that there are several common causes, including mold, mildew, dead animals, or trapped debris in the ductwork. This can lead to unpleasant odors throughout your home. The symptoms may include a persistent musty or rotten smell, especially when the HVAC system is running.
To address this issue, you'll first want to inspect the ductwork for any visible signs of mold, mildew, or other debris. If the problem is limited to a specific area, you may be able to clean or replace that section of ductwork yourself. However, if the smell is widespread or you suspect a more serious issue, it's best to call in a professional HVAC technician to fully inspect and clean the entire ductwork system.