AC vs Dehumidifier? Do You Need Both or One?

Is it Better to Have a Dehumidifier or Air Conditioner?

During the hot months of summer, there are 2 things that bothers homeowners: heat and humidity. Humidity levels vary from area to area with coastal areas like Florida having the highest relative humidity levels.

The thing about humidity is that it prevents our bodies from perspiring as they normally do. That is why hot and humid areas feels hotter than hot and dry areas.

Air conditioner and dehumidifier

Apart from that, humidity is not good for your health. The bacteria and viruses that cause respiratory infections thrive in air that has a relative humidity of 60% and above.

High humidity also encourages the growth of mold and mildew which damage furniture, paintwork, floors, carpets/rugs, brickwork and wallpaper. It can also cause musty smells in the house.

Both air conditioners and dehumidifiers can help deal with humidity. However, apart from reducing humidity, you will also need to cool your indoor air.

So, is it better to have a dehumidifier or air conditioner? And do you need a dehumidifier when you have an air conditioner?

An air conditioner is primarily designed to cool the indoor air but it also removes humidity. A dehumidifier is designed to remove humidity from the indoor air but does not cool the air. If you had to buy one, an air conditioner would be a good choice.

Sometimes you may need to have both an air conditioner and a dehumidifier depending on where you live. People living in hot and humid areas may need both an AC unit and a dehumidifier while those in hot and dry areas will need just the AC unit.

Air conditioners can be used as dehumidifiers. For example, a 2-ton air conditioner will lower humidity levels from 80% to 65%. Most central ACs will remove anywhere between 5 and 20 gallons of condensate (from humidity) in a day.

Running an air conditioner and dehumidifier concurrently is usually a good idea. The AC unit will initially lower the humidity to about 65% then the humidifier will kick in and lower the humidity further to the comfortable 40-50% levels.

How an Air Conditioner Works

Both air conditioners and dehumidifiers have similar parts and even work the same way but there is a slight difference. Let us now look at how both work starting with air conditioners.

Although there are several types of air conditioners, all work the exact same way. However, in this case I will focus more on central and mini-splits.

Air conditioners have 4 main parts:

  • Evaporator coil
  • Compressor
  • Condenser coil
  • Expansion valve

A refrigerant/coolant (also known as Freon) is circulated between the 4 components where it changes state from liquid to gas and back to liquid again, effecting heat exchange.

The refrigerant absorbs heat from indoor air (inside the evaporator unit), evaporates and enters the compressor where it is compressed increasing its pressure.

An increase in pressure also causes the temperature to rise. Increasing the temperature more than the surrounding hot air allows the refrigerant to lose the heat absorbed from indoor air. As you know, heat moves from a point of high concentration to a point of low concentration.

From the compressor the refrigerant enters the condenser coil. Both the condenser and evaporator are located outside the house so that the heat absorbed inside the house can be released outdoors.

As the refrigerant flows through the condenser coil, it loses the heat it absorbed indoors to the surrounding air. A fan mounted at the top of the unit blows cooler air across the coil which accelerates the process.

After losing the heat and becoming a liquid, the refrigerant goes through an expansion valve, which is basically a small opening/restriction. That causes the pressure of the refrigerant to drop.

A reduction in refrigerant pressure also means a drastic drop in temperature as well. At that point, the refrigerant will be a cold liquid ready to go back inside the evaporator coil for another round of cooling.

As the cold refrigerant enters the coil, the evaporator fan pulls warm and humid air from the house. When the air comes into contact with the coil, the refrigerant absorbs heat from the air and that is how cooling happens.

The cooled air is forced out of the indoor unit and back to the house. However, its humidity will have been reduced.

When the hot and humid air comes into contact with the cold coil, the water vapor (humidity) in the air condenses and drips from the coil to the condensate drain pan located under the evaporator coil.

An AC drain line will then remove the water from the drip pan and drain it outside the house or into the main house drainage system.

And that is how an air conditioner cools the indoor air removes humidity.

How a Dehumidifier Works


As I mentioned, humidity makes air feel hotter than it actually is. And that is where a dehumidifier can make a difference.

Dehumidifiers are primarily designed to remove humidity from indoor air, hence making the air dry. Although ACs will remove humidity from the air, dehumidifiers are just better at it.

Dehumidifiers work almost the same way as air conditioners (especially portable air conditioners). They however don’t cool the indoor air, and can even make it hotter.

A dehumidifier, just like an AC has a compressor, evaporator coil and a condenser coil making the unit very compact and portable. While an AC is controlled by a thermostat, dehumidifiers are controlled by a sensor known as a humidistat.

When the humidistat senses that the relative humidity in the house is higher than it should be, it turns on the unit. The dehumidifier has a fan which pulls indoor air towards it.

The air first goes through a filter where dust, dander, pollen and other particles are removed. From there the air is forced through the cold evaporator coil where the air is cooled.

When hot and humid air is cooled, the moisture in the water condenses and drips into a bucket which needs to be manually and periodically emptied. Some dehumidifiers also give you the option to connect a drain hose to the unit for continuous dehumidification.

So, what happens after the air is cooled?

In air conditioners, the condenser coil is located outside the house so that the heat absorbed by the refrigerant can be released to the outdoor air. However, in dehumidifiers the condenser coil is located inside the house and has no exhaust hose unlike portable ACs.

And that is the difference between air conditioners and dehumidifiers.

When the refrigerant (in dehumidifiers) loses heat inside the condenser coil, the same heat is used to heat the air which was cooled by the evaporator coil. As you can see, dehumidifiers will not cool your house.

Dehumidifiers pull in hot and humid air but releases hot and dry air.

Do I need a Dehumidifier if I have an Air Conditioner?

The answer for this question which you may might not like is “it depends”. Some people will need it while some will not.

So, when are you likely to need both an air conditioner and a dehumidifier?

First, if you relative humidity is above 60% you need a dehumidifier. That is more like a rule of thumb.

If you live in a hot and extremely humid area like Florida, your air conditioner will cool you indoor air but relative humidity will still be high. In such a case, you may need to have both an AC unit and a dehumidifier.

The air conditioner will lower the humidity from the highs of 80% to about 65% then the dehumidifier will take over and reduce it further to about 50% or even lower as you may wish.

The following are the states with highest relative humidity in the United States:

  • Alaska
  • Florida
  • Iowa
  • Mississippi
  • Louisiana
  • Hawaii
  • Michigan
  • Indiana
  • Vermont
  • Maine

In such states, it makes sense to have an air conditioner and a dehumidifier.

However, if you live in hot and dry areas (desert locations) which have low relative humidity, an air conditioner is all that you need.

The following are the states which have the lowest relative humidity levels in the United States:

  • Nevada
  • Arizona
  • Utah
  • New Mexico
  • Colorado
  • Wyoming
  • California
  • Montana
  • Oklahoma
  • Idaho

You may also need a dehumidifier if you or a member of the family has allergies, especially mold or dust mite allergies. Mold thrives in humid areas and that is why you need a dehumidifier to lower the relative humidity.

Do you get condensation on your windows? You have too much moisture in your indoor air which can be removed by a dehumidifier.

You may also need a dehumidifier if you have a moldy/musty smell in your house, especially in the basement. Although you will first need to get to the root of the problem, you will have to install a dehumidifier to prevent it from coming back.

Is It Cheaper to Run an Air Conditioner or Dehumidifier?

It is way cheaper to run a dehumidifier than an air conditioner. Dehumidifiers are compact and they don’t need a lot of power to function.

Air conditioner use more electricity that dehumidifiers. Both coils have a fan which is powered by an electric motor, while the compressor (which is bigger than that of a dehumidifier) also uses more power to compress the refrigerant.

I however don’t see why the cost of running each should be problem since you will need both of them, or just the air conditioner which is more expensive to run.

Although the dehumidifier is cheaper to run, it will only lower your relative humidity but will not cool the air. That will not solve your problems. You will still need to run the AC to cool the indoor air.

Wrap Up

And basically that is everything about the air conditioner versus dehumidifier debate. What is important is that you need to lower you indoor air temperature and relative humidity.

To do that, you will need both an air conditioner and a dehumidifier or just the air conditioner depending on where you live. I don’t see a scenario where you will only need a dehumidifier.

So going back to the original question, it is better to have an air conditioner instead of a dehumidifier.