Air Conditioners Remove Some Moisture, But They're Not Dehumidifiers
An air conditioner does remove moisture from the air as a side effect of cooling, but it is not designed to work like a dehumidifier and will not control humidity the way a dedicated unit does. When an air conditioner cools air, that air passes over cold coils, and moisture condenses on those coils the same way water beads on a cold window. That water drains away, leaving the air slightly drier. However, an air conditioner stops removing moisture the moment the room reaches your target temperature—it shuts off and stays off until the temperature rises again.
A dehumidifier, by contrast, runs continuously to pull moisture out of the air regardless of temperature. It will keep working in a 72-degree room with 70% humidity because its only job is humidity control. An air conditioner in that same room would not run at all, and the humidity would climb. This difference matters most in spring and fall, when outdoor temperatures are mild but humidity is high, or in basements and bathrooms where moisture lingers even when the space is cool enough.
Key Takeaways
- Air conditioners remove moisture only while cooling; they stop working once the room reaches the set temperature, leaving humidity uncontrolled.
- Dehumidifiers run continuously to lower humidity independent of temperature, making them the right tool for damp spaces that don't need cooling.
- In humid climates, running an air conditioner alone often leaves indoor humidity above the comfortable 30–50% range even when the room feels cool.
- Basements, bathrooms, and laundry rooms usually need a dehumidifier because they stay cool but trap moisture that an air conditioner won't address.
- Some modern air conditioners have a dedicated dehumidify mode that runs the compressor at low power to remove moisture without aggressive cooling.
How an Air Conditioner Removes Moisture
An air conditioner cools air by circulating it over refrigerated coils inside the unit. As warm, humid air passes over those cold coils, the moisture in the air condenses into liquid water, similar to how a bathroom mirror fogs and then drips after a hot shower. That water collects in a drain pan and flows out through a condensate drain line, usually to the outside or into a floor drain.
The amount of moisture removed depends on how much the air is cooled and how long the unit runs. A 10-degree temperature drop removes more moisture than a 2-degree drop because colder air cannot hold as much water vapor. In a humid climate on a hot day, an air conditioner can remove several gallons of water per day. But the moment the room reaches your set temperature, the compressor stops, the coils warm up, and moisture removal stops entirely.
Why Air Conditioners Fall Short in Humid Climates
In regions with high humidity and moderate temperatures—coastal areas, the Pacific Northwest, or the upper Midwest in spring—an air conditioner alone often cannot bring indoor humidity down to a comfortable level. Comfortable indoor humidity sits between 30% and 50%. If outdoor humidity is 80% and the temperature is 72 degrees, your air conditioner will not run because the room is already cool. The indoor humidity will stay at 70% or higher, and you will feel sticky and uncomfortable.
Even in hot, humid climates, an air conditioner may not remove humidity fast enough. If the outdoor air is 95 degrees and 80% humid, the air conditioner will cool the room but may only drop humidity to 55–60%, still above the comfort zone. The unit prioritizes temperature over humidity, so it shuts off as soon as cooling is done, leaving moisture behind.
Spaces Where a Dehumidifier Works Better Than an Air Conditioner
Basements are the clearest example. A basement stays naturally cool because it is below ground, so an air conditioner has little reason to run. But basements trap moisture from the soil and groundwater, and that moisture builds up unchecked. A dehumidifier will run continuously in a cool basement and pull that moisture out of the air, preventing mold, musty smells, and damage to stored items.
Bathrooms and laundry rooms have the same problem. A hot shower or a load of laundry releases a burst of moisture, but the room cools quickly. An air conditioner will not run, and the humidity lingers for hours. A dehumidifier will catch that moisture before it settles on walls and creates mold.
Crawl spaces, attics in humid climates, and rooms with poor air circulation also benefit from a dehumidifier because they need moisture control independent of temperature. If you live in a humid climate and your air conditioner is running constantly but the air still feels damp, a dehumidifier in the problem room or a whole-house dehumidification system paired with your air conditioner will make a real difference.
The Dehumidify Mode on Some Air Conditioners
Many modern air conditioners, especially window units and some central systems, include a dehumidify mode. In this mode, the compressor runs at reduced power, cooling the air just enough to condense moisture without aggressively lowering the temperature. The fan then circulates that slightly cooler, drier air back into the room.
Dehumidify mode is useful in mild weather when you want to lower humidity but do not want the room to get cold. It uses less energy than full cooling mode and can bring humidity down by 10–15 percentage points over a few hours. However, it is still not as effective as a dedicated dehumidifier because it relies on cooling to remove moisture, and it will not work if the room is already at or below your comfort temperature.
Choosing Between an Air Conditioner and a Dehumidifier
If your main problem is heat, an air conditioner is the right tool. If your main problem is moisture in a cool space, a dehumidifier is the right tool. If you live in a hot, humid climate and your air conditioner is running but the air still feels damp, you may need both—the air conditioner to cool and a dehumidifier to finish the job of removing moisture.
Check your indoor humidity with an inexpensive hygrometer (a small meter that measures moisture in the air). If humidity stays above 55% even when your air conditioner is running, a dehumidifier will make a noticeable difference in comfort and help prevent mold and mildew. If humidity is already in the 30–50% range, your air conditioner is doing enough, and a dehumidifier is not necessary.
Frequently Asked Questions
Can I use an air conditioner instead of a dehumidifier in a basement?
Not effectively. A basement stays cool naturally, so an air conditioner will rarely run. Even if it does, it will shut off once the temperature is met, leaving humidity high. A dehumidifier runs continuously and is designed for this job. If your basement is also hot, a combination of both may work, but a dehumidifier alone is usually the better choice.
Will running my air conditioner on dehumidify mode work as well as a dehumidifier?
Dehumidify mode helps, but it is not a full replacement. It works best in mild weather when you want to lower humidity without heavy cooling. In very humid conditions or in cool spaces, a dedicated dehumidifier will remove moisture faster and more consistently because it does not depend on temperature to operate.
Why does my air conditioner run all day but the house still feels humid?
Your air conditioner may be cooling the air but not removing enough moisture. This happens in very humid climates or when outdoor humidity is high. The solution is to pair your air conditioner with a dehumidifier, or to have your HVAC system checked to may support the condensate drain is clear and the unit is sized correctly for your space.
Does a dehumidifier use a lot of electricity?
A portable dehumidifier typically uses 300–700 watts, similar to a window air conditioner but less than a central air system. Running one continuously in a single room costs roughly $10–20 per month depending on your local electricity rates and the unit's size. Larger whole-house dehumidifiers use more power but serve the entire home.
Can I run my air conditioner and dehumidifier at the same time?
Yes, and in hot, humid climates it is often necessary. The air conditioner cools the air, and the dehumidifier removes the moisture the air conditioner leaves behind. They work together without conflict. Just make sure the dehumidifier drain is clear so water does not back up into the unit.