The Short Answer
Your air conditioner removes moisture from indoor air as it cools. When the system is oversized, poorly maintained, or its drain line clogs, humidity climbs and condensation forms, creating conditions where mold can grow. Keeping indoor humidity in the 30 to 50 percent range is a common target.
Why humidity is the real issue
Mold needs moisture. In a state where outdoor humidity is high most of the year, the air inside your home is only as dry as your HVAC system makes it. A house that feels cool but clammy is a house with a humidity problem.
Common HVAC causes of moisture
- Oversized systems that cool quickly and shut off before removing enough moisture.
- Clogged condensate drain lines that back up into the air handler closet.
- Uninsulated or leaking ductwork that sweats in attics.
- Dirty coils and filters that reduce how well the system dehumidifies.
- Thermostat setbacks that let humidity build while you are away.
Simple habits that help
Buy an inexpensive hygrometer and check readings in a few rooms. Keep the thermostat fan on Auto rather than On, since continuous fan operation can push moisture back into the air. Change filters on schedule, and have the drain line flushed during routine service.
If you leave home for extended periods, avoid turning the AC off completely. A moderate setting keeps humidity in check while saving energy.
When to have it evaluated
Persistent readings above 60 percent, musty air from vents, water around the air handler, or condensation on vents and windows all suggest it is time for a closer look. An indoor air quality evaluation documents humidity behavior and identifies where moisture is accumulating.