Why Is My House So Humid With The AC On? 9 Causes Revealed

Humidity is an issue that we need to deal with all year round. We have to combat dryness in cold months and dampness on warmer days. When people feel their homes are humid, they frequently turn on the air conditioner. It does not, however, always work.

Why is your house so humid with the AC on? The reasons may lie in the AC itself or the external factors.

In this post, I will analyze the causes and provide advice on how to solve the problem. Let’s get started!

Causes of high humidity in the house with ac running

There are various causes why your room is humid. But some of them can be mitigated by turning on the AC. This section will look at the causes of high humidity when the air conditioner is on.

1. Frozen evaporator coils

The evaporator coil is an important part of AC, absorbing heat from the air inside your home. It contains liquid refrigerant and will convert it to gas to complete the heat exchange and dehumidification process.

When the evaporator coils are frozen, the system’s efficiency suffers and the dehumidifying process is hampered. Frozen evaporator coils can be caused by a lack of airflow, a dirty air filter, a low outside temperature, and other factors.

To solve this problem, you should turn off your AC immediately and wait for the coil to thaw. Then you can inspect the problem and turn it back on when it is resolved.

2. Dirty condenser coils

dirty condenser coil

This is a similar issue to the frozen evaporator coil we discussed above. Condenser coils, another important part of the heating exchange process in your AC, release the heat absorbed into the outdoor environment, and the refrigerant changes from gas to liquid form.

When the condenser coils accumulate dirt and dust, it will impede the refrigerant cycle, leading to the lower efficiency of dehumidifying. 

Cleaning the condenser coils on a regular basis can keep this problem at bay. 

3. AC is too small 

If the air conditioner in your house or your room is too small, it is not able to handle such an amount of air. Accordingly, it can’t suck up as much moisture as you want. 

It means it works, but it cannot provide the level of comfort you seek.

4. Oversized AC 

It seems to be a bit contradictory, but an oversized air conditioner cannot effectively extract water vapor.

The AC will shut off automatically when the target temperature is reached and then shut off when the temperature rises to a certain level. 

Assume you have an AC that can cool 1000 square feet installed in a room with 250 square feet. This unit can cool down your room in a short time without having enough time to suck up the excess humidity. 

As a result, choosing a proper-sized AC unit is crucial for its dehumidifying performance. 

5. Too many people in the house

Have you ever noticed that your air conditioner struggles to keep the room cool when you have a lot of visitors?

The number of people in the house has a significant impact on the performance of your air conditioner because our breath and sweat disperse more moisture and heat in the atmosphere.

When only one or two people live in the house, their effects are negligible. Nonetheless, the effects become apparent as more people gather.

6. Wrong fan settings

If you have a central HVAC system installed, you can run the fan separately, allowing air to blow out of the vents even when the AC is turned off.

In this case, the air will not be cooled and dehumidified. The air is just as musty as before. 

To avoid making the same mistake in the future, set the fan to “AUTO” so that it only operates when the AC is turned on.

7.  Your ductwork has been damaged

Even if your AC is working hard to remove water, moisture from the outside will get into your home if the ducts have cracks or leaks. You should inspect the ducts and pipes in your room on a regular basis. This is also a good way to keep your AC from overloading.

8. Your daily activities

Your daily routine, like cooking and showering, is possible to keep your house humid even if the AC is working.

These activities can produce excess moisture every so often, which may be more than you imagine. That’s why you feel the air is damper when you step into the bathroom or kitchen. 

To get rid of it, your house needs proper ventilation. Running the exhaust fan is a simple and effective way to regulate indoor humidity.

9. Humid climates

The outdoor air will creep into your house in many ways. The outdoor humidity will affect the indoor humidity to some extent

When the outside is too wet, the indoor humidity will go up to a certain level that your AC is not capable of handling, just as the AC is too small.

How to use AC when humidity is high?

You can use your air conditioner in “dry mode” or set the temperature to 2-3°C lower than the current temperature.

Also, remember to set the fan speed to a low setting. This gives your air conditioner enough time to drain the condensation on the coils.

Aside from that, regular coil cleaning and filter replacement are essential for its dehumidifying efficiency.


This post summarized nine causes of high humidity in the house when AC is on. 

While air conditioning can be used to remove excess moisture, a unit that is too small or too large will not function properly. Cleaning that is overdue can cause the evaporator coils to freeze and clog the condenser coils, making the AC less efficient.

When your house is overcrowded, it is normal to see indoor air become humid as your AC may not be able to remove the extra moisture caused by guests as fast as you expect. The humidity outdoors and your daily routine will also play a role. 

About The Author

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Liz Yang is the founder of Airsmartly. She has been working at home for a few years and realizes that the performance of the HVAC system plays such an important role in our life. She has tested dozens of products in person, like humidifiers, air purifiers, dehumidifiers, and ACs, and wants to share tips about using or troubleshooting these products with you. Her uncle is an HVAC expert with over 30 years of experience in the field, and often offers assistance when she is unsure how to handle a situation. He is also in charge of reviewing the articles on this site.

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