Why Does Your Nose Get Stuffy at Home? Why It Might Be Your AC

How Your AC Can Contribute

A Dirty or Low-Quality Air Filter

The filter is your system’s first defense against dust, pollen, and pet dander. Once it clogs, it catches less and can restrict airflow. A thin fiberglass filter may stop large debris but let fine particles pass right back into your rooms.

Mold or Mildew in the Coil and Drain Pan

Your AC removes moisture from the air, and that water collects on the indoor coil and drains through a pan and a line. If the drain clogs or the coil stays dirty, the damp surfaces can grow mold or mildew. The system then blows air across them all day. A musty smell when the AC starts is a common clue.

Humidity That Is Too High

Dust mites and mold thrive in humid air. Indoor humidity is generally recommended to stay between about 30% and 50%. An oversized air conditioner can cool the house quickly without running long enough to remove moisture, leaving it cool but damp, a common issue in humid St. Louis summers. Learn more in What BTU Means and Why Sizing by Square Footage Gets It Wrong.

Leaky Ductwork

Ducts that run through an attic or crawlspace can pull in dust, insulation fibers, and other particles through gaps and loose joints, then deliver them to your living space.

Cold, Dry Air Blowing on You

For some people, cold air or a sudden temperature change can trigger congestion on its own, even with clean air. A vent aimed at your bed or favorite chair can make it worse.

Signs Your System May Be Involved

• Symptoms improve when you leave the house
• A musty or mildew smell when the AC kicks on
• Visible dust around supply vents, or dust that returns soon after cleaning
• Rooms that feel cool but clammy
• Water in the drain pan or around the indoor unit

What You Can Do at Home

1. Change the filter on schedule. Every one to three months is typical, more often with pets or during heavy pollen seasons. A pleated filter in the MERV 8 to 13 range catches far more fine particles than basic fiberglass. Check with a technician before going higher, since some systems lose airflow with denser filters.
2. Measure your humidity. An inexpensive hygrometer shows whether your home stays in the 30% to 50% range.
3. Keep vents and returns clean. Vacuum grilles and keep furniture from blocking them.
4. Redirect vents that blow straight onto beds or seating.
5. Schedule seasonal maintenance. A tune-up that includes cleaning the coil and checking the condensate drain addresses two of the most common sources of musty air. See our maintenance plans.

When to Call a Technician, and When to See a Doctor

Call an HVAC technician if you notice a persistent musty smell, visible mold near the indoor unit, standing water in the drain pan, or humidity that stays above 50% while the AC runs. A technician can clean the coil and drain, check for duct leaks, and recommend options such as upgraded filtration, a whole-home dehumidifier, or UV lights. See our indoor air quality services.

See your doctor if congestion lasts for weeks, comes with fever, facial pain, or trouble breathing, or does not improve after your air is addressed. Improving indoor air may help many people feel more comfortable, but it is not a substitute for medical care.