Graham FisherBy Graham Fisher

Updated November 2026

Running an air conditioning and dehumidifier together is one of the most effective ways to control indoor humidity, especially in hot, humid climates. This guide explains how the two appliances remove moisture differently, when you need one, the other, or both, and how to set them up so they don’t fight each other. By the end, you’ll know how to pick the right settings and how to tell whether your home is actually getting drier.

Why Air Conditioning Removes Some Moisture but Not Enough

An air conditioner does dehumidify, but that’s a side effect of cooling. Warm air holds more water vapor than cold air. As the air passes over the cold evaporator coil, moisture condenses and drains out through the condensate line. The cooler the coil, the more water it pulls from the air.

Shopping for one? See our guide: Air Dehumidifier vs Air Purifier (2026): Which Is Better for Your Home?.

The problem is that a standard air conditioner is sized to cool, not to dry. When the thermostat reaches its setpoint, the compressor shuts off, and the fan may keep running without removing much humidity. On mild, humid days, the system may cycle on and off in short bursts, so it never runs long enough to bring humidity down. Many homes end up at 60 percent relative humidity or higher even with the AC running, which is above the 30 to 50 percent range most indoor air guidelines recommend.

How a Dehumidifier Works Alongside Your AC

A dehumidifier pulls in room air, cools it over a coil to condense moisture, and then reheats the air slightly before releasing it. Because it does this on a dedicated schedule, it can keep pulling moisture from the air even when the AC isn’t running.

Your AC and dehumidifier do different jobs:

  • Air conditioner: lowers temperature and removes moisture as a byproduct of cooling.
  • Dehumidifier: targets humidity directly, regardless of temperature.

Used together, the dehumidifier can run in rooms or on days when the AC cools without drying enough, and the AC keeps the space comfortable while the dehumidifier handles the moisture load.

Step-by-Step: Setting Up Air Conditioning and Dehumidifier Use Together

Step 1: Measure Your Current Humidity

Before changing any settings, find out where you stand. A basic digital hygrometer, the kind sold for less than a few dollars at hardware stores, will show relative humidity in each room. Place one in the main living area, one in the bedroom, and one in a basement or other problem zone if you have one. Take readings in the morning and evening for a few days.

Step 2: Check Your AC Settings

Many people keep their thermostat on “Auto” fan. Switching the fan to “On” can actually reduce dehumidification, because the blower runs continuously and re-evaporates moisture off the coil back into the air. Set the fan to “Auto” so the coil stays wet and pulls moisture efficiently during cooling cycles.

Next, avoid setting the thermostat too high on humid days. A slightly lower setpoint, such as 74 to 76°F instead of 80°F, lets the AC run longer and remove more water. Some newer systems include a dedicated dehumidify mode that reduces fan speed and runs the compressor at a cooler level, which removes more moisture while holding temperature steady. Check your manual for this feature.

Step 3: Size and Place the Dehumidifier

Dehumidifiers are rated by how many pints of water they remove per day under standard test conditions. Manufacturers typically specify capacity at 80°F and 60 percent humidity, so real-world performance will vary. As a rough guide:

Space Typical Pint Rating Needed
Single room up to 500 sq ft 20 to 30 pints per day
Basement up to 1,000 sq ft 40 to 50 pints per day
Whole home or very damp basement 50 to 70 pints per day, or a whole-house unit

Place the unit in the center of the room with at least 6 to 12 inches of clearance on all sides so air can circulate. Keep doors and windows closed while it runs. In a basement, place it away from the furnace and water heater if possible.

Step 4: Set Humidity Targets and Let Each Unit Do Its Part

Set the dehumidifier to 45 to 50 percent relative humidity. Going much lower can dry out your skin and make wood furniture crack. Set your thermostat for comfort first, then let the dehumidifier maintain the humidity target. If the AC is running and the dehumidifier is also running, the two will work in the same direction, and the AC can run less often because the air is already drier.

Step 5: Confirm Results Over One Week

Watch the hygrometer readings. If humidity stays above 55 percent most of the day, either the dehumidifier is undersized, the room is leaking humid air from outside, or the AC coil needs cleaning. Check the dehumidifier’s bucket and drainage each day, and empty or connect a hose as needed.

Factors That Affect How Well the Two Work Together

  • Climate: In humid regions, the AC may need help year-round. In dry climates, a dehumidifier may only be needed in basements or during rainy seasons.
  • Home sealing: Leaky ducts, unsealed crawl spaces, and open vents pull in outside moisture that both units must fight.
  • AC age and size: An oversized AC short-cycles and removes little moisture. Ask an HVAC technician to check sizing if your system is very old or was installed without a load calculation.
  • Ventilation: Bathroom and kitchen exhaust fans should vent outside, not into the attic or crawl space.
  • Occupancy: Cooking, showers, and plants add moisture. A family of four produces a lot more humidity than a single occupant.

Checklist: Tools and Supplies You’ll Need

  1. Digital hygrometer for each key room
  2. Dehumidifier sized for your space
  3. Drain hose and a floor drain or sump, if you want continuous drainage
  4. Replacement AC air filter (typically changed every 1 to 3 months)
  5. Soft brush or vacuum for cleaning the dehumidifier intake grille
  6. Tape measure to confirm room square footage

Common Mistakes to Avoid

  • Running the AC fan on “On” all the time, which reduces moisture removal.
  • Setting the dehumidifier too low, which over-dries the air and can cause discomfort.
  • Placing the dehumidifier against a wall or in a closet, which chokes airflow and shortens runtime.
  • Ignoring a clogged or dirty AC filter, which reduces airflow across the coil and cuts dehumidification.
  • Skipping the drain connection, which means the bucket fills and the unit shuts off mid-cycle.
  • Assuming a bigger AC will dry the house better. Oversizing often makes humidity worse.

Tips for Better Results

  • Run bathroom fans for 20 minutes after showers to remove moisture at the source.
  • Keep indoor plants and fish tanks in mind. They add moisture, and some owners move plants to a different room during humid months.
  • Clean the AC condensate drain line once a year to prevent clogs and water damage.
  • If you have persistent musty smells, check for mold. Mold growth is more likely above 60 percent humidity, and a professional should evaluate any significant growth.

A digital hygrometer lets you verify the results of your setup rather than guessing. Look for a model that reads relative humidity, not just temperature.

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A dehumidifier with a continuous drain option removes the need to empty the bucket by hand, which matters when the unit runs for many hours a day. Check that it includes a hose fitting.

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A high-efficiency pleated AC filter improves airflow over the coil compared with thin fiberglass filters, which helps the system remove moisture. Replace it on schedule.

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FAQ

Does running an air conditioner dehumidify the air?

Yes. As the air cools over the evaporator coil, moisture condenses and drains away. However, the AC is designed mainly to cool, so it may not reduce humidity enough in very humid conditions.

Should I run the AC fan on auto or on?

Auto is better for dehumidification. With the fan on continuously, moisture can re-evaporate off the coil back into the air.

Can I run a dehumidifier and air conditioner at the same time?

Yes, and it is a common setup. The AC handles temperature and some moisture, while the dehumidifier targets humidity. Running both can lower humidity faster, though energy use will rise.

What humidity level should I aim for indoors?

Most guidance suggests 30 to 50 percent relative humidity. Many people find 45 to 50 percent comfortable and effective for limiting mold and dust mites.

Will a dehumidifier make my AC work harder?

A dehumidifier adds some heat to the room because it generates warmth while running. In most homes the effect on AC load is small, and drier air often feels cooler, so you can raise the thermostat slightly.

Is an air conditioner enough to prevent mold?

It can help, but it is often not enough on its own in humid climates or damp basements. Keeping humidity below about 50 to 60 percent and fixing water leaks are the main steps. A professional should assess any visible mold. For health concerns, consult a doctor or certified mold inspector.

How often should I empty a dehumidifier?

Empty it whenever the bucket indicator lights up, or use a continuous drain hose to avoid manual emptying altogether.

Do I need a dehumidifier if I already have central air?

Not always. If your hygrometer shows humidity staying below 50 to 55 percent, your AC may be sufficient. If humidity stays high, or you have a damp basement, a dehumidifier is a practical addition.

Conclusion

An air conditioner cools first and dehumidifies second, so it often needs help in humid conditions. Adding a properly sized dehumidifier, setting the AC fan to auto, and checking results with a hygrometer gives you direct control over indoor moisture. Measure first, make one change at a time, and confirm that humidity settles in the 45 to 50 percent range.

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Graham Fisher

About Graham Fisher

Graham Fisher is part of our editorial team and reviews and edits our indoor air guides, checking product details against manufacturer specifications and owner feedback.