Find the Problem
Every odor has a source. When you notice a musty smell coming from your vents, the first thing you need to do is locate the source of the smell. This will help you to assess what steps need to be taken to resolve the issue. Follow the path of your air ducts through your home and check each output vent to get an idea of where the smell starts. If it is present at every vent, the issue may be with the central air-conditioning unit or intake.
Check for Leaks
One of the most likely causes of musty odors in the home is the presence of mold. Mold grows in moist environments and is often caused by small leaks in either your plumbing or your home's exterior. Carefully examine your walls and attic space for any signs of a leak. If you find a leak, have it fixed immediately by someone who is qualified to do the task. For instance, hire a plumber to fix leaky pipes, or a roofer to fix the roof.
If you cannot find a source for the odor, it is possible that your air ducts need to be cleaned. Hire a licensed professional with excellent references to conduct this process; a poorly trained or incompetent contractor could damage your air ducts and leave you stuck with thousands of dollars in repair bills. As a rule, you should have your ducts cleaned if there is visible mold, they are infested with mice or insects, or you notice dust being expelled into your home.
A musty odor needs to be identified as quickly as possible. Musty odors mean something is going wrong somewhere in your home, and these problems could lead to long-term health problems for you and your family. If anyone in your family is having intense allergy attacks or is continually feeling ill with no discernible reason, these issues could be linked to particles in your air system. Remember that safety should be your first priority, so family members should see a doctor if these symptoms arise.