Odor – Musty odor from your ductwork can be a serious sign for mold inside your system, especially while you run the system.
Visible – Visible mold on the ‘vent grilles’ or on the ceiling can point on the fact there is a mold colony inside the system. In this case you can open the covers and check it out or either call to an expert to inspect it.
Illness – Mold can cause some serious problems as itchy eyes, headaches, red eyes, runny nose and even respiratory problems. If someone feels one of these symptoms you should call to an expert for an inspection.
Water leaks – If you had water leak or any water damage in your house – call to professional to inspect and fix it, or, to ensure that no damage was caused.