A dehumidifier reduces the workload on your air conditioner, but it does not replace it
Your air conditioner already removes moisture from the air as it cools—that is why you see water dripping from the outdoor unit on humid days. A dehumidifier removes additional moisture without lowering the temperature. In a very humid climate, or in a room where moisture builds up faster than your AC can handle it, a dehumidifier can make your air conditioner work less hard to reach the temperature you want. The two machines work toward the same goal but in different ways.
The real benefit is not that a dehumidifier makes your AC cooler. It is that your AC reaches your target temperature with less runtime, which lowers your electric bill and extends the life of the unit. In dry climates, or in rooms where humidity is already under control, a dehumidifier adds no real value.
Key Takeaways
- Air conditioners remove some moisture as they cool, but a dehumidifier removes moisture without cooling, so the two can work together in humid spaces.
- When humidity is high, your AC has to run longer to reach your set temperature because it is doing two jobs at once—cooling and dehumidifying.
- A dehumidifier is most useful in basements, bathrooms, or climates where humidity stays high even after cooling.
- Running both machines together uses more total electricity than running the AC alone, so a dehumidifier only saves money if it reduces how often your AC runs.
- If your air conditioner cannot keep humidity below 50 to 60 percent, a dehumidifier may help; if humidity is already controlled, one will not.
Why air conditioners remove moisture in the first place
When warm, humid air passes over the cold evaporator coil inside your air conditioner, the moisture condenses into liquid water—the same way a cold glass of water beads up on the outside on a hot day. That water drains out of the system and away from your house. This happens automatically whenever your AC runs, with no extra effort or cost.
However, an air conditioner is designed to cool first and dehumidify second. It removes moisture as a side effect of cooling, not as its main job. If the air in a room is already cool but still humid—common in basements, crawl spaces, or after rain—your AC may not run long enough to pull out enough moisture. That is where a separate dehumidifier comes in.
When a dehumidifier actually reduces your AC's workload
Humid air requires more energy to cool than dry air. When your thermostat is set to 72 degrees, your AC will run longer in 80 percent humidity than it will in 50 percent humidity, because the air has more moisture to remove before it feels comfortable. A dehumidifier removes that moisture first, so your AC can reach 72 degrees faster and then shut off.
This matters most in climates where humidity stays high even after the sun goes down—the Southeast, parts of the Midwest, and coastal areas. It also matters in specific rooms: bathrooms after a shower, basements that stay damp, or laundry rooms where moisture builds up. In these spaces, running a dehumidifier for an hour or two can lower the humidity enough that your AC runs 10 to 20 percent less often.
In dry climates like the Southwest, or in well-sealed homes with good ventilation, humidity is rarely a problem, and a dehumidifier will not change how often your AC runs at all.
The electricity cost of running both machines
A dehumidifier uses electricity—typically 300 to 700 watts, depending on size and how hard it is working. Running it continuously costs more than running your AC alone. The only way a dehumidifier saves money is if it reduces how often your AC runs by enough to offset its own power use.
In a humid basement or bathroom, this trade-off often works out: a small dehumidifier running 4 to 6 hours a day may use less total electricity than an AC that would otherwise run 30 percent longer. In a living room where humidity is already controlled by your AC, adding a dehumidifier will straightforward increase your electric bill.
If you are considering a dehumidifier, check your current humidity level with an inexpensive hygrometer (a humidity meter, usually $10 to $20). If it stays above 60 percent even after your AC has been running, a dehumidifier may help. If it is already below 50 percent, one will not.
How to know if your AC is struggling with humidity
Your air conditioner is struggling with humidity if the indoor temperature reaches your set point but the air still feels clammy, sticky, or uncomfortable. You may also notice condensation on windows, a musty smell, or visible mold growth in corners or on walls. These are signs that moisture is not being removed fast enough.
Another sign is that your AC runs almost constantly on hot, humid days but never quite reaches the temperature you set. This happens because the unit is working at maximum capacity just to cool the air; it does not have extra cooling power left over to remove moisture.
If you see these signs, measure the humidity with a hygrometer. Comfortable indoor humidity is between 30 and 50 percent. If your AC keeps it between 50 and 60 percent, it is working hard but managing. If it stays above 60 percent, a dehumidifier could help.
The right way to use a dehumidifier with your AC
If you decide to use a dehumidifier, run it in the room or zone where humidity is highest, not throughout the whole house. A basement dehumidifier should stay in the basement; a bathroom dehumidifier should run after showers. Do not try to dehumidify your entire home with a single portable unit—it will not work, and you will waste electricity.
Set the dehumidifier to maintain 45 to 50 percent humidity, and let it run on its automatic setting so it turns off once that level is reached. Do not set it lower than 40 percent; very dry air can damage wood furniture, musical instruments, and drywall joints.
Empty the water tank regularly, or connect a drain hose to a floor drain or sump pump if the unit has that option. A full tank will shut the machine off and leave moisture in the air.
When to call a professional about humidity problems
If your air conditioner cannot keep humidity below 60 percent even when it is running constantly, the problem may not be the AC itself. It could be that your home has too much moisture coming in from outside, or that air is leaking in around doors and windows faster than the AC can condition it. It could also mean your AC is undersized for your climate, or that the evaporator coil is dirty and not removing moisture efficiently.
A heating and cooling technician can check whether your AC is working correctly, clean the coil if needed, and tell you whether a dehumidifier will actually help or whether you need a larger unit. They can also check for air leaks or ventilation problems that are bringing in too much outside humidity.
Frequently Asked Questions
Will a dehumidifier cool my house?
No. A dehumidifier removes moisture but actually produces a small amount of heat as a side effect. It will not lower the temperature; it will only make the air feel less sticky. If you need to cool your home, you need an air conditioner.
Can I use a dehumidifier instead of an air conditioner?
No. A dehumidifier removes moisture but does not lower temperature. In summer, you need an air conditioner to cool your home. A dehumidifier can only supplement an AC in very humid climates.
Should I run my dehumidifier and AC at the same time?
Yes, if humidity stays above 60 percent even when your AC is running. Run the dehumidifier in the specific room where humidity is highest, and set it to maintain 45 to 50 percent. Running both uses more electricity, but it may use less total power than running your AC longer to do both jobs.
What size dehumidifier do I need?
Dehumidifiers are rated by how many pints of water they remove per day. A small room (100 to 150 square feet) needs 30 to 50 pints per day; a medium room (150 to 250 square feet) needs 50 to 75 pints per day. Check the manufacturer's chart for your room size and current humidity level.
Does a dehumidifier help with mold?
A dehumidifier can prevent mold from growing by keeping humidity below 50 percent, but it will not remove mold that is already there. If you see mold, clean it with a mold-killing cleaner and fix the source of moisture—a leak, poor ventilation, or condensation. Then use a dehumidifier to keep it from coming back.