HVAC Dehumidifier – Signs You Need It, Pros & Cons

If you live in a humid area, you most likely need to have a dehumidifier despite having an air conditioner. While AC units can remove humidity from the indoor air, they will not reduce it to the ideal levels. However, people in arid areas will don’t need a dehumidifier. The AC will take care of humidity.

I am sure you have heard of the line “It’s not the heat, it’s the humidity”. This especially applies to homeowners in coastal areas like Florida where relative humidity is high.

whole house dehumidifier
Whole-house dehumidifier with a condensate pump

Relative humidity makes it feel hotter than it actually is. That is because the high moisture level in the air prevents our bodies from regulating their temperature through perspiration.

So, do you need a dehumidifier? The following are the signs that you need to have a humidifier.

  • Indoor relative humidity is higher than 55%
  • Discomfort (body feels sticky and you struggle to sleep)
  • Mold growth indoors
  • Musty smells in the house
  • Condensation on windows
  • Oversized air conditioner
  • Worsening asthma and/or allergies
  • Water damage

A dehumidifier is an appliance used to reduce the relative humidity in the house. You can opt to have a whole-house dehumidifier or a stand-alone portable dehumidifier.

Portable dehumidifiers are plugged directly to a power outlet while whole-house dehumidifiers are added directly to the HVAC system. They draw warm and humid air from the return air duct and remove moisture from it thereby reducing its relative humidity.

Folks who don’t need a dehumidifier will need a humidifier. A humidifier does the exact opposite of what a dehumidifier does – increase relative humidity indoors.

You see, relative humidity change with changes in temperature. During the months of summer when temperature is high, relative humidity is high especially in humid states like Florida but manageable in arid areas like Arizona.

However, when temperatures drop in winter, the air in the arid states will be dry and the relative humidity so low that it can cause the skin to crack, eyes to dry, respiratory infections and other effects. A humidifier is used to add water vapor in the air therefore increasing the relative humidity.

How a Dehumidifier Works

how a dehumidifier works

A dehumidifier works exactly like an air conditioner. It pulls warm air from the house, cools it down for the water vapor to condense, drain the condensate and then release the dry air back to the house.

The only difference between a dehumidifier and an air conditioner is that a dehumidifier does not cool the air while air conditioner’s primary function is cooling. Dehumidifiers can therefore not be used as an alternative to air conditioners.

Related: AC vs dehumidifier

A dehumidifier has a cooling coil, a heating coil, a compressor and a fan. When the relative humidity in the house exceeds the set level, the fan kicks in and start drawing in air from the house.

The cooling coil contains a cold liquid known as a refrigerant/coolant. When the indoor air comes into contact with the cold coil, the water vapor in the air condenses (turns from gas to liquid).

If you have a whole-house dehumidifier, the water will be drained into a floor drain or elsewhere depending on where the dehumidifier is. However, portable dehumidifiers have a bucket where the condensate drains into.

If you don’t want to keep draining the bucket manually, you can connect a drain hose from the dehumidifier to the outside or the house’s drainage system.

Here is how a dehumidifier differs from an air conditioner.

Air conditioners have an outside unit where the refrigerant dumps the heat it absorbed from the indoor air. Dehumidifiers don’t have that.

Instead of releasing the heat outside, the heat is used to heat the air (which was cooled in order for the water vapor to condense). Therefore, dehumidifiers take in warm and humid air and release warm but dry air.

Do You Need a Dehumidifier if You Have an Air Conditioner?


The answer to this question is “it depends”. Some people will need just a good air conditioner while others will need both an air conditioner and a dehumidifier.

It depends on the relative humidity levels where you live. If you live in an area where relative humidity is high (like Florida, Louisiana and Mississippi), you most likely need both a dehumidifier and an air conditioner.

However, folks who live in arid areas like Arizona, Nevada and New Mexico, an air conditioner will be enough to control the relative humidity in the house.

Just like dehumidifiers, air conditioners have a cooling coil (evaporator) inside the house which apart from cooling the indoor air also reduces humidity. A central AC unit can produce anywhere between 5 to 20 gallons of water in a day.

An air conditioner is however not as efficient in humidity reduction as a dehumidifier. In humid states, an air conditioner will reduce the relative humidity from about 80% (or higher) to about 65%.

You would then need a dehumidifier to reduce the humidity further to the acceptable levels (30 to 50%).

For a state like Arizona whose average humidity of 38.5% is already within the comfortable range, a dehumidifier will not be needed. You just need the AC to lower the indoor air temperature.

As I mentioned, these states with low humidity may not need a dehumidifier but will surely need a humidifier for when winter comes. On the other hand, homes in humid states like Florida will most likely not need a humidifier.

Portable vs Whole-House Dehumidifiers

portable dehumidifier
portable dehumidifier

A portable dehumidifier looks and works pretty much like a portable AC unit. It can be installed just about anywhere in the house as long as there is a power outlet.

A whole-house dehumidifier on the other hand is installed on the HVAC system where it draws warm and humid air from the house and remove moisture from it. As a result, a whole-house dehumidifier as its name implies removes humidity in the entire house, the way a central AC cools the entire house.

Portable/stand-alone dehumidifiers are designed to reduce the relative humidity of only a certain area of the house like the basement or laundry room.

Installation of a whole-house dehumidifier is expensive since it needs to be done by a professional HVAC contractor. Stand-alone dehumidifiers don’t need any installation. All you have to do is plug them to a power outlet.

Another thing to consider is the cost. Portable dehumidifiers cost $300 on average but you may need to pay more if you need a technician or handyman to connect a drain hose to a floor drain or even outside.

Whole house dehumidifiers costs between $1300 and $2800 depending on size and brand. It will further cost you an extra $500 to $700 for installation labor.

Whole-house dehumidifiers are however more energy efficient than stand-alone dehumidifiers. On average, a whole-house dehumidifier will cost $10 a month to run a while a stand-alone dehumidifier will cost $30.

Signs You Need a Dehumidifier

So, do you need a dehumidifier? How can you tell if you need a dehumidifier on your HVAC system?

The following are the tell-tale signs that you need a dehumidifier in your house:

1. High Relative Humidity

The ideal relative humidity for homes is between 30% and 50%. Ideal relative humidity is expressed as a range since people have different comfort levels, just like with temperature.

Some people even claim that the best relative humidity for indoors is 45% to 55%. I would even go ahead and say that 60% is high but you can live with it.

If however the relative humidity in your house is above 60%, you clearly need a dehumidifier. A house with relative humidity levels higher than 60% are just not pleasant to live in.

Modern digital thermostats will not only indicate the indoor temperature but they will also indicate the relative humidity. You can also tell your indoor humidity using a humidistat.

2. There is Mold in the House

mold on a wall

Mold thrives when the humidity in the surrounding air is high. That is why mold is usually a problem in bathrooms and other damp areas of the house.

Needless to say, you need to lower your indoor humidity if you want to starve molds. And the way to do that is by installing a dehumidifier.

If the mold are a problem in certain area of the house like the basement, a portable dehumidifier will be enough to solve the problem. However, if the molds are in different areas of the house, install a whole-house dehumidifier.

3. Worsening Cases of Asthma and Allergies

Mold and dust mites which increases with high humidity can trigger allergies and asthma cases in your household. If you notice that you or your family members are coughing and/or sneezing especially when indoors, you may need to install a dehumidifier.

By lowering the relative humidity indoors, allergy triggers like dust mites will reduce considerably.

4. Musty Smells Indoors

The growth of mold and mildew indoors has direct effect on the quality of your air. That is manifested by musty smells especially in the basement where mold are more likely to thrive.

Note: If the musty smell is coming from your air registers, you may have a mold problem in your HVAC system especially the AC drain line. Cleaning it with vinegar will fix the problem.

5. Condensation on Windows

If there is condensation (water forming on the inside of your windows), the relative humidity in the house is way too high. When the humid indoor air comes into contact with the cold windows, the moisture in the air condenses and water starts to drip from the window.

Condensation can also be seen on toilet tanks, a phenomenon commonly known as “sweating toilets”. The moisture in the air condenses on the surface of the tanks which contain cold water.

6. Oversized Air Conditioner Unit

You may think that a big air conditioner unit is a big thing but that is hardly the case. Apart from being inefficient, a big AC unit does not reduce humidity the way a properly sized unit would.

The problem with an oversized AC unit is that it only needs to run for a few minutes to cool the air and then it will turn off. To remove humidity however, an AC unit needs to run for a long time.

If replacing your oversized AC unit with a proper size is not an option, you will need to install a dehumidifier. That will take care of the humidity as the AC cools the house.

7. General Discomfort

Our bodies produce sweat to help them regulate their internal temperature. That however only works if the sweat evaporates from the skin which creates a cooling effect.

However, if the relative humidity is too high, the sweat will not evaporate and that is why our bodies feel sticky and we feel lazy or sickly. It is also hard to sleep well when humidity is high.

8. Water Damage?

Are there water stains in your walls and ceilings even though there are no water leaks in the house? You could be having high relative humidity in your house.

When the relative humidity in your house is high, moisture will condense on the cold surfaces inside your surfaces and later start dripping on ceilings, walls and other surfaces. Eventually when humidity levels drop and the surfaces dry, ugly stains will be left behind.

Apart from attracting mold, this problems also leaves you with repairs to do every year. I would recommend installing a dehumidifier and forgetting about the issue for good.

Wrap Up

I hope by now you understand if you need a dehumidifier and an air conditioner or just an air conditioner. You also know if you need a humidifier or not. Hopefully, this article was helpful.