An outdoor central air air conditioner unit to the left and a dehumidifier in a home to the right

Air conditioners certainly cool indoor air, but do they dehumidify as well?

And if so, just how effective are they? At what point should you install a home dehumidifier?

Do Air Conditioners Also Dehumidify?

Yes, to an extent.

Air conditioners dehumidify as they cool the air. Reducing moisture is a side effect of cooling the air, as cold air simply cannot hold as much moisture as warm air.

During the AC cycle, excess moisture is collected in the coil (the part that sits above your furnace) and drains out. This reduces quite a bit of humidity but not as much as a dehumidifier will.

Dehumidifiers and air conditioners are built and operate fairly similarly, but they aren’t meant to provide the same function. So let’s explore their similarities and differences a bit more in-depth. 

Why Air Conditioners Dehumidify

Let’s talk a little about the refrigeration cycle and how air conditioners work. Air conditioners dehumidify because they cool the indoor air significantly before releasing it back into the room. Cool air can’t hold moisture like warm air can, so the moisture is removed.

But, how does that work?

Air conditioners use a very cold refrigerant that absorbs heat and expels it outside at the condenser. The refrigerant cycles through copper lines and coils connecting the two systems. There are coils in both the outdoor condenser and the indoor evaporator.

When the air passes over the evaporator coils, it becomes so cold that a lot of the moisture is automatically released onto them. This moisture is collected in a pan beneath the evaporator and drains out into your basement drain or condensate pump.

If you’re unfamiliar with the refrigerant cycle, this might sound confusing. But don’t worry—we’ll be diving into that in just a moment. 

Dehumidifiers and air conditioners both contain those copper coils filled with refrigerant. They are similar in this aspect, but there are a few key differences.

What Is the Refrigeration Cycle, and How Does It Work?

The refrigeration cycle is the process of circulating warm air through coils (that have been cooled down significantly) and then releasing that cooled air back into the atmosphere. 

There are four components to the refrigeration cycle: 

  • The compressor
  • The condenser
  • The expansion valve
  • The evaporator

These four components actively work together to cycle and cool the air. How does this work? 

The compressor controls the flow of the refrigerant. It does this by functioning as both a motor and pump. The compressor takes the refrigerant and compresses it, as its name suggests. 

Illustrated diagram of the Refrigeration Cycle
Courtesy of InterNACHI

The condenser works to condense the refrigerant after it has already cycled through the compressor. When the refrigerant is released from the compressor, it’s become sweltering and fully pressurized. The condenser cools the refrigerant into a liquid state. 

The expansion valve releases some of the pressure of the refrigerant and cools it even more. 

Finally, the evaporator turns the refrigerant back into a gas and releases it into the coils and it circulates back through the system.

How Dehumidifiers Work

Both dehumidifiers and AC systems run on the refrigeration cycle. Which is also true for any appliance that works to cool air temperature, for example, your refrigerator. 

While both machines work with the refrigeration cycle, the process is quite different. The way the air is brought in and circulated throughout the device is an entirely different process with dehumidifiers versus air conditioners. 

How A Dehumidifier Works

Dehumidifiers remove humidity the same way air conditioners do. They pull in moist air and run it over a cold coil and release it back into the room. The moisture that has been removed collects into a water tank at the bottom of the unit.

A homeowner opens the water collection chamber of a dehumidifier to empty it

One of the main differences between dehumidifiers and AC is that dehumidifiers take the air and heat it back up before releasing it into the room. If the humidifier didn’t reheat the air, it would be a portable AC instead.

If you’re still having trouble understanding, just remember that AC systems produce cool, dry air and dehumidifiers produce warm, dry air.

How Much Does an Air Conditioner Dehumidify?

Dehumidifying is a side benefit of running your air conditioner. It isn’t its main purpose. If you live in a humid climate, you will likely need to get a dehumidifier to reduce you humidity levels. The AC won’t be able to keep up and will have to work harder to cool your home.

How much moisture is removed by being run through the air conditioner depends on a few factors. 

First, the air conditioner’s size relative to the room you are cooling. Bigger AC units will remove more moisture as they cool the air, but they’re also going to shut off as soon as the temperature gauge has registered that the room is cool enough. This is called short cycling and is just as bad as having a unit that is too small.

Smaller models, on the other hand, are going to run constantly and still won’t be able to reduce humidity levels.

Dirty air filters and coils can prevent the unit from dehumidifying the room well, if at all. Make sure to check and change your furnace filter regularly. And keep an eye on the outdoor condenser. Do you see any grass clippings, seeds, or other debris in the unit? If so, take a garden hose and spray it until the debris washes down.

Closeup on a mini-split compressor with a homeowner cleaning it by spraying water into the grille.

Do I Need a Dehumidifier?

If you live in a humid climate, the answer is likely Yes. Even if your AC is sized properly, it will still struggle to keep up with cooling demands if the humidity levels are extreme. 

Humidity levels in your home should be kept below 60%.

If your AC fails to do that, you will need to invest in a dehumidifier. You can install a whole-home unit that connects to your duct work, or you can get a more affordable, portable unit. 

A dehumidifier will help take the strain off your AC, which will save you money on utility bills, as well as prolong the life of your AC unit.

The evaporator coil of an air conditioner in the grass outside a home
A central air evaporator coil. Courtesy of Rescue Air

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