Why does my AC smell musty?

A musty smell from your AC is typically caused by mold or mildew growth somewhere in your system, most commonly in the evaporator coil, ductwork, or drain pan. This happens when moisture gets trapped in dark, cool areas of your HVAC system and creates the perfect breeding ground for these microorganisms.

The most frequent culprit is dirty evaporator coils inside your indoor unit. When these coils get coated with dust and debris, they retain moisture longer after cooling cycles, allowing mold spores to take hold. Your air filter also plays a role - a clogged filter restricts airflow, causing the coils to stay wet longer and potentially allowing contaminants to bypass the filter entirely.

Ductwork issues are another common source, especially if you have leaky ducts that allow humid air to enter, or if there's been water damage in your home. The condensate drain pan and drain line can also harbor mold growth if they're not draining properly or haven't been cleaned regularly.

In Ottawa's humid summers, this problem becomes more pronounced because your AC works harder to remove moisture from the air. If you haven't had professional duct cleaning in the past 3-5 years, accumulated debris in your ducts could be contributing to the musty odor.

Start by replacing your air filter and checking that your condensate drain isn't backed up. However, if the smell persists, you'll need professional attention. Mold in your HVAC system can affect indoor air quality and potentially trigger respiratory issues. A licensed HVAC technician can inspect your evaporator coils, clean your system thoroughly, and identify any ductwork problems that need addressing.

For persistent musty odors, consider professional duct cleaning and sanitization to eliminate mold spores throughout your system. Want to discuss your specific situation? We offer free consultations to assess air quality concerns in Ottawa homes.