Does this match your problem?
- House feels sticky even at 72°F
- Windows fog on the inside
- Musty smell in closets or basements
- Visible mold spots on drywall or vents
- Bathrooms take hours to dry after showers
Quick check first
Buy a $15 hygrometer (or use a smart thermostat with humidity readout). If you're consistently above 55% in summer, this guide is for you.
Step-by-step troubleshooting
1. Set your thermostat fan to AUTO (not ON)
When the fan runs continuously, moisture that condenses on the cold evaporator coil evaporates back into the airstream during the AC's off cycles. AUTO fan mode lets water drain properly. This one setting change fixes a huge number of humidity complaints.
2. Confirm your AC is the correct size
An oversized AC cools the room quickly then shuts off, before it has time to remove humidity. If your AC runs in short 5–10 minute bursts, it may be oversized. Longer, steadier runtimes dehumidify better.
3. Find where humid air is leaking in
On a hot day, run your hand along the edges of exterior doors, window frames, and attic hatches; feel for warm, damp air pushing in. Look at accessible duct joints for loose tape or gaps. Every one of those gaps is a path for humid outdoor air, and return-side leaks in a crawlspace are the worst offenders because they pull humid crawlspace air straight into the airstream. Identify the leaks first, then the air-sealing and duct-sealing procedures are covered in the DIY Quick-Fix Playbook, or we can seal them properly during a visit.
4. Use bathroom and kitchen exhaust fans
Run the bath fan during every shower and for 20 minutes after. Use the range hood while cooking. A single shower can add a pound of water to your indoor air.
5. Check your crawlspace
In Raleigh, an unencapsulated crawlspace is often the #1 humidity source in the house. If your vapor barrier is torn, missing, or wet, or if you can smell mildew from the vents, encapsulation typically drops upstairs humidity 10–15 points.
6. Add a whole-home dehumidifier
If humidity stays above 55% after the steps above, install a ducted whole-home dehumidifier. Portable units help one room; whole-home units (Aprilaire, Santa Fe) tie into your ductwork and control the entire house. This is a permanent fix, not a repair.
Stop and call a licensed pro if:
- •Humidity stays above 60% for weeks despite AC running
- •You see mold growth on walls, vents, or under sinks
- •AC runs in 5–10 minute cycles and won't run longer
- •Crawlspace has standing water or heavy mildew smell
- •New construction or recent renovation and humidity spiked