Humidity, Mold & Indoor Air Quality in Baton Rouge, LA

The goal: under 60 percent

The EPA recommends keeping indoor relative humidity below 60 percent, ideally between 30 and 50 percent (EPA, A Brief Guide to Mold, Moisture and Your Home). Outdoor humidity in Baton Rouge is often far higher, especially on summer mornings and during rainy spells, so the house depends on the AC to remove moisture. A digital hygrometer from a hardware store shows you the number.

Why the house stays humid

• The system is oversized and short-cycles before removing much moisture.
• The fan is set to "on," so water on the coil re-evaporates into the house between cycles. "Auto" is usually better here.
• Airflow is set too high for humid conditions.
• Return ducts leak and pull in humid attic air.
• Moisture sources like unvented bathroom fans, dryers venting indoors, and air leaks around doors, windows and attic hatches.
• Raised homes where humid crawlspace air works its way up through the floor.

Musty smells and mold around the system

A musty or "dirty sock" smell when the AC starts often comes from microbial growth on a damp indoor coil or in a drain pan that holds water. Black spots on supply registers usually mean condensation on a cold surface. The EPA's guidance is to fix the moisture problem first and then clean up; areas larger than about 10 square feet, or mold inside the HVAC system, call for more careful work (EPA, A Brief Guide to Mold, Moisture and Your Home). See the musty smell guide.

Solutions

• Fan on "auto," clean filters and correct blower settings.
• Clean the coil and drain pan and keep the condensate line flowing.
• Seal and insulate ducts, especially returns. See ductwork.
• Whole-home dehumidifier connected to the ducts, which removes moisture during mild, damp weather when the AC barely runs.
• Variable-speed equipment at replacement time for longer, drier cycles.
• Exhaust fans that vent outdoors in bathrooms and kitchens.

Filters and air cleaners

Pleated filters in the MERV 8 to 13 range catch far more fine particles than basic fiberglass filters, but very restrictive filters can choke airflow on some systems. The EPA notes that HVAC filters and portable air cleaners can reduce airborne particles, but they work best alongside source control and ventilation (EPA, Guide to Air Cleaners in the Home). Air cleaners do not fix a humidity problem.

Related guides

• Why Does My AC Smell Musty? A Baton Rouge Guide
• Getting Your AC Ready for a Baton Rouge Summer

Sources: EPA, A Brief Guide to Mold, Moisture and Your Home; EPA, Guide to Air Cleaners in the Home.