Air conditioning removes some moisture, but not always enough

Air conditioning does pull moisture out of the air as a side effect—when warm air passes over cold evaporator coils inside your unit, water condenses and drains away. But air conditioning is designed to cool your home to a set temperature, not to control humidity. Once your home reaches that temperature, the air conditioner stops running, even if the air is still damp. In humid climates or during wet seasons, this means your AC may not run long enough to bring humidity down to a comfortable level.

A dehumidifier works differently. It runs independently of temperature and removes moisture continuously, regardless of whether cooling is needed. This matters because high humidity can persist even in a cool room—you might feel clammy at 72°F with 70% humidity, but comfortable at 75°F with 45% humidity.

Key Takeaways

  • Air conditioning removes moisture only while running to cool your home, so it may not dehumidify enough in naturally humid climates.
  • You need a dehumidifier if your home stays above 50% to 60% relative humidity even when your AC is running regularly.
  • Basements, bathrooms, and crawl spaces often need separate dehumidifiers because AC doesn't reach them effectively.
  • A whole-home dehumidifier integrated into your HVAC system works alongside AC and runs independently of cooling cycles.
  • Portable dehumidifiers work in single rooms and are the cheapest option if you only have moisture problems in one or two areas.

When your AC is enough on its own

If you live in a dry climate—the Southwest, parts of the Mountain West, or inland areas with low annual rainfall—your air conditioner alone will likely keep humidity at a comfortable level. Comfortable indoor humidity sits between 30% and 50% relative humidity. In these regions, AC running during warm months will naturally bring humidity down to that range.

You can check your home's humidity with an inexpensive hygrometer, a small device that reads relative humidity and costs $10 to $30. Place it in a central room away from bathrooms and kitchens, and check it over a few days during normal use. If it consistently reads below 60%, your AC is handling humidity adequately.

When you should add a dehumidifier

Add a dehumidifier if your hygrometer reads above 60% relative humidity regularly, even when your AC is running. This happens in humid climates—the Southeast, Gulf Coast, Pacific Northwest, and parts of the Midwest—where outdoor air naturally carries more moisture. It also happens during spring and early summer before temperatures climb high enough to run the AC constantly.

High humidity causes visible problems: mold and mildew on bathroom tiles and window frames, musty smells in closets, sticky-feeling air, and condensation on windows. It also worsens allergies and asthma because dust mites and mold thrive above 50% humidity. If you see any of these signs, a dehumidifier will make a real difference in comfort and air quality.

Whole-home versus portable dehumidifiers

A whole-home dehumidifier connects to your existing HVAC ductwork and runs independently of your air conditioner. It pulls moisture from air circulating through your system and drains it away continuously. This approach costs $1,500 to $3,000 installed and works throughout your entire home. It's the best choice if humidity is a problem in most rooms, or if you want a single solution you don't have to monitor or empty.

A portable dehumidifier sits in one room, pulls moisture from that space, and collects water in an internal tank or drains via a hose. They cost $150 to $600 depending on capacity and run only the rooms where you need them. They work well for basements, bathrooms, bedrooms, or laundry rooms—the places where moisture tends to collect. The trade-off is that you have to empty the tank regularly (usually every 12 to 24 hours in very humid conditions) or run a drain hose to a floor drain or window.

Basements and crawl spaces need their own solution

Basements and crawl spaces are the most common places where AC alone fails. These areas are naturally cooler and sit below ground level, where moisture from soil seeps through walls and floors. Your home's main air conditioning system may not reach these spaces effectively, or air moves through them too quickly to remove much moisture.

A portable dehumidifier in a basement or crawl space will run almost constantly in humid months and is often necessary to prevent mold, musty odors, and structural damage. If you have a finished basement, a 50-pint dehumidifier (one that removes 50 pints of water per day) is a reasonable starting point; an unfinished basement or crawl space may need a 70-pint or larger unit. Run a drain hose to a sump pump, floor drain, or window well so you don't have to empty the tank by hand.

Bathrooms and kitchens after showers and cooking

Bathrooms spike in humidity during and after hot showers, and kitchens do the same while cooking. Your AC may not run long enough or pull air from these rooms fast enough to handle the sudden moisture load. This is why bathrooms often develop mold on grout and caulk, and why kitchens smell musty.

The first step is to run your bathroom exhaust fan during and for 20 minutes after every shower, and your kitchen exhaust fan while cooking and for 10 minutes after. These fans vent moisture directly outside and are far more effective than relying on AC. If mold or mildew still appears despite running fans, a small portable dehumidifier in the bathroom or a larger one in a central hallway can help. Many people find that fixing exhaust fan use solves the problem without needing a dehumidifier at all.

How to choose between options

Start by measuring humidity in the rooms where you suspect a problem. If readings are consistently above 60% in most of your home, a whole-home dehumidifier makes sense. If humidity is high only in a basement, bathroom, or one bedroom, a portable unit is cheaper and faster to set up.

If you rent or don't want to install ductwork, portable dehumidifiers are your only option. If you own your home and humidity is widespread, a whole-home unit integrated into your HVAC system will run more efficiently over time because it doesn't have to be emptied or monitored. Talk to an HVAC contractor about whether your existing ductwork can accommodate a whole-home dehumidifier, and what the installation would cost in your area.

Frequently Asked Questions

Can I run my AC fan on continuous to dehumidify without cooling?

Yes, but it's not very effective. Setting your thermostat to "fan only" keeps air moving across the evaporator coil, which removes some moisture. However, the coil is coldest when the compressor is running, so continuous fan mode removes far less moisture than running the full AC cycle. It also uses electricity without providing cooling. A dehumidifier is more efficient for this purpose.

Will a dehumidifier make my electric bill much higher?

A portable dehumidifier uses 300 to 700 watts depending on size and humidity level, similar to a window air conditioner. Running one continuously for a month might add $10 to $30 to your bill, depending on your local electricity rates. A whole-home dehumidifier integrated into your HVAC system uses less energy because it works with your existing ductwork and doesn't have to run as hard.

Do I need a dehumidifier if I have a basement sump pump?

A sump pump removes standing water but does not remove humidity from the air. A wet basement will still feel damp and smell musty even with a working sump pump. You need a dehumidifier to pull moisture out of the air and prevent mold growth on walls, floors, and stored items.

What size dehumidifier do I need?

Dehumidifiers are rated by pints per day—how much water they remove. A 30-pint unit works for a small bedroom or bathroom; a 50-pint unit handles a basement or large room; a 70-pint or larger unit is needed for very damp basements or crawl spaces. Check the manufacturer's recommendations for room size and humidity level, and choose the next size up if you're between two options.

Can I use my air conditioner less if I have a dehumidifier?

Not really. A dehumidifier removes moisture but does not cool air, so you still need your AC to reach your desired temperature. However, once your home is cool enough, a dehumidifier can run independently to keep humidity down while your AC cycles on and off less frequently. This may save a small amount of energy compared to running AC continuously to fight humidity.