A dehumidifier can reduce the load on your AC, but it does not replace it

A dehumidifier and an air conditioner do different jobs. Your AC cools the air and removes some moisture as a side effect. A dehumidifier removes moisture without cooling. If your AC is already running, adding a dehumidifier will not cool your home faster or lower your electric bill — it will raise it. However, a dehumidifier can help in two specific situations: when your AC cannot keep humidity low enough on its own, or when you want to reduce how hard your AC has to work during mild weather.

The key question is whether your AC is already handling the humidity in your space. If your home feels damp even when the AC is on, or if you see condensation on windows, your AC may be undersized for your climate or your home may have a moisture source (like a basement leak or poor ventilation). In those cases, a dehumidifier addresses the problem your AC cannot solve alone. If your home feels comfortable and dry with the AC running, a dehumidifier will only waste energy.

Key Takeaways

  • An air conditioner removes moisture as it cools, so a dehumidifier does not make cooling faster or cheaper if your AC is already working well.
  • A dehumidifier helps only if your AC cannot keep humidity below 50 to 60 percent, which happens in very humid climates or when your AC is undersized.
  • Running both a dehumidifier and an AC at the same time increases your electric bill because you are powering two machines instead of one.
  • A dehumidifier can reduce AC runtime during spring and fall when the weather is mild but the air is damp, saving energy in those seasons.
  • Before buying a dehumidifier, measure your indoor humidity with an inexpensive meter to confirm it is actually above 60 percent when your AC is on.

How an air conditioner removes humidity

Your AC cools air by running it over cold coils. As warm air passes over those coils, moisture condenses on them — the same way water beads on a cold glass. That water drains out of your system, and drier air comes back into your home. This is why running your AC makes your home feel less sticky, even though cooling and dehumidifying are not the same process.

The amount of moisture your AC removes depends on how long it runs. If your AC runs for eight hours a day, it removes moisture for eight hours. If it runs for two hours, it removes less. This is why an undersized AC unit — one that cools your home quickly but does not run very long — may not remove enough moisture in a humid climate. The air gets cold enough, but the coils do not have enough time to pull out the water.

When a dehumidifier actually helps your AC

A dehumidifier makes sense if your indoor humidity stays above 60 percent even when your AC is running. You can measure this with a hygrometer, a small meter that costs $10 to $30 and hangs on a wall. If your AC is on and your humidity is still 65 or 70 percent, your AC is not removing enough moisture. This happens most often in coastal areas, in the Southeast, or in homes with moisture sources like basements or bathrooms that do not vent outside.

In those cases, a dehumidifier in the room where you spend the most time (usually the bedroom or living room) can bring humidity down to a comfortable level without running your AC longer or colder. You run the dehumidifier for a few hours in the evening, it pulls water out of the air, and you feel more comfortable. Your AC still does the cooling; the dehumidifier handles the moisture your AC could not.

A dehumidifier also helps during shoulder seasons — spring and fall — when the weather is cool enough that you do not need much AC, but the air is still damp. Instead of running your AC all day to control humidity, you can run the dehumidifier alone for a few hours. This uses less energy than running both machines.

Why running both machines at once wastes energy

If your AC is already keeping your home at a comfortable humidity level, turning on a dehumidifier will not improve anything. Both machines will be working to remove moisture that is already being removed. You will pay for the dehumidifier's electricity without getting any benefit in comfort or cooling speed.

The math is straightforward: your AC uses 3,000 to 5,000 watts when it runs. A typical dehumidifier uses 500 to 700 watts. Running both at the same time costs you the power of both machines. If you run them together for four hours a day for three months, you will add $30 to $60 to your electric bill for no gain in comfort.

How to know if you need a dehumidifier

Before you buy, measure your humidity. Buy a hygrometer for $15 to $25, place it in the room where you spend the most time, and check it at different times of day for a week. Write down the readings when your AC is on and when it is off. If your humidity stays above 60 percent even when the AC is running, a dehumidifier may help. If your humidity is below 50 percent with the AC on, you do not need one.

Also check for moisture sources. If you see condensation on windows, water stains on walls, or smell mustiness, the problem may not be humidity alone — it may be a leak, poor ventilation, or a basement that needs a sump pump. A dehumidifier will mask the symptom but not fix the cause. Address the source first, then measure humidity again.

If you live in a very humid climate (like Florida or Louisiana) and your AC is sized correctly for your home, you may find that your humidity naturally stays between 50 and 60 percent, which is acceptable. You do not need a dehumidifier. If your humidity climbs above 65 percent, then a dehumidifier becomes worth the cost.

Dehumidifier size and placement matter

A dehumidifier works best in a single room or small area, not a whole house. If you buy a unit rated for 1,500 square feet but your home is 3,000 square feet, it will not keep humidity low in rooms far from where it sits. Most people use a dehumidifier in the bedroom at night or in the living room during the day, not running it constantly.

Place the dehumidifier away from walls and furniture so air can flow around it. Keep a window or door open to the rest of your home if you want it to affect multiple rooms, but expect the effect to weaken the farther you go. Empty the water tank or attach a drain hose so you do not have to empty it by hand every day.

Alternatives to running a dehumidifier and AC together

If your humidity is high, you have other options before buying a dehumidifier. First, check that your AC filter is clean. A clogged filter reduces airflow over the cold coils, which means less moisture removal. Replace the filter every three months or when it looks dirty.

Second, make sure your AC is sized correctly. If your home cools to 72 degrees in two hours and then stays there, your AC is oversized and does not run long enough to remove much moisture. An undersized AC runs all day but never quite cools enough. A correctly sized unit runs about 40 to 60 percent of the time. If you think your AC is the wrong size, have an HVAC technician measure your home's cooling load.

Third, reduce moisture at the source. Run your bathroom and kitchen exhaust fans while you shower or cook, and vent them outside (not into the attic). Seal air leaks around windows and doors so humid outside air does not leak in. Fix any plumbing leaks or roof leaks. These steps cost less than a dehumidifier and address the real problem.

Frequently Asked Questions

Will a dehumidifier make my AC run less often?

No. Your AC runs based on temperature, not humidity. If your thermostat is set to 72 degrees, your AC will run until the home reaches 72 degrees, whether or not a dehumidifier is on. A dehumidifier removes moisture but does not change when your AC cycles on and off.

Can I use a dehumidifier instead of AC in summer?

No. A dehumidifier removes water from the air but does not cool it. In summer heat, you need your AC to lower the temperature. A dehumidifier alone will not make your home comfortable and may make it feel warmer because the machine generates heat as it runs.

What humidity level should I aim for?

Between 30 and 60 percent is comfortable for most people. Below 30 percent feels dry and can irritate your skin and sinuses. Above 60 percent feels sticky and can encourage mold and dust mites. If your AC keeps you in that range, you do not need a dehumidifier.

How long does a dehumidifier take to lower humidity?

A dehumidifier rated for your room size will lower humidity by 5 to 10 percent in two to four hours. The exact time depends on the room size, how wet the air is, and how much the dehumidifier is rated to remove per day. Check the specifications before you buy.

Is it cheaper to run a dehumidifier or lower my AC temperature?

Lowering your AC temperature by a few degrees will cool the air faster, which removes more moisture as a side effect. This uses more energy than running a dehumidifier alone, but it also cools your home. If you want both cooling and lower humidity, lowering the AC temperature is more efficient than running both machines separately.