The short answer
How AC Affects Humidity
Air conditioners cool the air and pull out some moisture as part of that process. But the amount of moisture removed depends on how long the unit runs and how warm the air is. If your AC cycles on and off quickly, it may cool the room without giving the coils enough time to condense water out of the air.
An oversized AC can cool a room too fast, so it shuts off before it has a chance to dehumidify. An undersized unit may run constantly but still struggle to keep up on hot days. Both situations leave you with air that feels clammy even when the temperature is comfortable.
- Set the fan to auto so the unit runs longer per cycle
- Keep the thermostat a few degrees cooler to extend run time
- Close windows and doors to keep humid outdoor air out
- Use exhaust fans in the kitchen and bathroom while cooking or showering
- Check that the condensate drain is clear and not backing up
Indoor Moisture Sources
Everyday activities add surprising amounts of water vapor to your home. Showers, boiling pasta, drying clothes indoors, and even houseplants release moisture that your AC must handle. If you have several people living there, the combined effect can push humidity higher than the system can manage.
A hidden water leak can also raise humidity without being obvious. A slow drip behind a wall, under a sink, or in the basement adds moisture continuously. You might notice the humidity first before you see any water stain or musty smell.
HVAC Settings and Maintenance
Your AC works well when the evaporator coils are cold and clean. Dirty filters or coils reduce airflow, so the unit cools less and removes less moisture. Changing or cleaning filters monthly during heavy use helps keep the system efficient.
The temperature setting matters too. If you set the thermostat just a degree or two below the outdoor temperature, the AC may not run long enough to dehumidify. Try setting it a few degrees lower and see if the humidity drops. Also, check that the fan is on auto, not on, so the unit runs longer per cycle.
When to Call the Pros
If you have checked the obvious causes and the humidity still feels high, there may be a deeper issue. A water leak inside a wall, under the subfloor, or in the ceiling can saturate building materials and keep releasing moisture into the air. Local water damage pros can use moisture meters to find hidden damp spots.
The pros can also set up structural drying and dehumidification equipment to pull moisture out of walls and floors. This work often involves removing wet drywall or flooring to let the structure dry properly. In humid climates, indoor humidity issues can persist through multiple seasons.
Using a Dehumidifier
A portable dehumidifier can work alongside your AC to remove extra moisture, especially in basements or rooms where the AC never runs. Place it in the most humid area and set it to 50 percent relative humidity. Empty the water tank regularly or connect a hose to a drain.
For whole-house humidity control, a whole-house dehumidifier integrated with your HVAC system might be worth considering. That setup is more involved and usually requires a professional to install. Check your AC's manual for guidance on ideal humidity settings, and consider a hygrometer to track the actual level in your home.
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Call Now (617) 404-2753Frequently asked questions
Why does my AC cool but not dehumidify?
The AC may be running too short a cycle to condense water, or the coils are dirty. Check the filter and set the fan to auto. If it still doesn't help, the unit might be oversized for the room.
Can a hidden leak make my house humid?
Yes. A slow leak in a wall or under a floor adds moisture continuously. You might notice musty smells or higher humidity before visible stains appear. A moisture inspection can find the source.
Should I use a dehumidifier with my AC?
Often, yes. A dehumidifier helps in rooms where the AC doesn't run often, like a basement. Set it to around 50 percent humidity and keep the AC running as needed for cooling.