Why Is My House So Humid With The AC On?

A common question we get a lot from homeowners is, “Why is my house so humid with the AC on?” We understand how it’s common to feel uncomfortable when humidity levels are high in your own home. So stick around to get your answers!

There are several reasons why your air conditioning system will cause humidity in your home. But for starters, hotter air holds more moisture than cold air, so it becomes even more humid when the hot air cools.

This article will further discuss the various reasons for high indoor humidity even when your AC unit is running, so be sure to read on.

What Should Humidity be in House with Air Conditioning?

No matter what type of climate you live in, the relative humidity in the air can significantly affect the comfort of your lovely home. That is why the ideal indoor humidity levels should be between 30 and 50%.

Maintaining this humidity level should be your main priority, especially when tailoring your cooling and heating preferences to meet your personal home needs.

How Much Humidity is too Much? 

As we have mentioned before, the ideal level of humidity in your home should be between 30% to 50% which is the relative humidity that differs from the absolute humidity.

What do I mean? To understand the difference between absolute humidity and relative humidity, you must first know that air temperatures affect how much water vapor it can hold. Meaning cold air holds less water vapor while hot air holds more vapor.

Without further a due, absolute humidity measures the actual amount of water vapor in a cubic meter of air WHEREAS relative humidity measures how much water vapor is in the air compared to how much vapor could be in the air on its temperature.

So what does this mean? The exact amount of water in a cubic meter of air, the relative humidity will be higher if it’s cold air and lower if it’s warm air.

How High Humidity Affects Air Conditioning

High humidity can negatively affect the cooling potential of your HVAC system, and that is why air conditioner professionals recommend a humidity level that is below 60%. However, it’s not easy to maintain considering the changing weather conditions from time to time.

So, how does excess humidity affect air conditioners? Technically, air conditioners work by removing warm air from your house and blowing in refrigerated air, that is, cool air. Air conditioners also work to lower humidity levels to increase the efficiency of cooling efforts and make your home more comfortable.

The HVAC coil works to reduce humidity levels by condensing water vapor into liquid and then draining the excess with proper installation and sizing; this system provides excellent dehumidifying properties in every weather condition.

BUT when the humidity levels rise above normal, most systems cannot cope. This means that high humidity cancels out the air conditioner’s cooling effect. During high humidity levels, you will find yourself running the air conditioning unit harder for more extended periods and not getting the desired effects as you expected, and your house will start feeling muggy inside.

You will know when the humidity in your house is too high if you start feeling the air inside feels damp and moist and your windows are foggy.

Signs of High Humidity in your Home

Not having enough humidity in your house is terrible, so having too much humidity is arguably worse. The easiest way to determine whether your home is experiencing high humidity is by using a hygrometer, but if you do not have one, here are a few w signs you should look out for.

Smell of Mildew

It’s perfectly normal to have a bit of mildew in your house, especially in areas such as the crawl spaces and the basement, where airflow is pretty much limited. You will smell the mildew once you enter a room that lacks enough airflow. The mildew smell has a musty smell and feels damp, just like how a rotting wood would smell.

It becomes worse if you start smelling the mildew in rooms that initially were not having the smell. This is enough proof to alert you that there’s an increased moisture buildup in your home.

Condensation On Your Windows

If you have a poor sense of smell, then condensation on your windows would help you determine excessive moisture in your house. If the indoor humidity levels in the room are high, then moisture will start condensing on your windows and other surfaces you could think of.

The condensation mainly occurs in areas with the most prominent contrast in temperature o the surrounding air, e.g., windows, mirrors, and pipes.

How do I know condensation on my windows is due to excess humidity? If you notice what looks like fog clinging to your windows and will feel damp to the touch.

Visible Mold Growth

Smelling mold is one thing, but seeing it grow in your house is another unpleasant thing. Mold usually grows in frequently damp and warm areas such as the kitchen and bathrooms. However, if you start seeing mold growing in other areas of your home, then that proves that there are excess humidity levels in your home.

Discoloration and Spotting of Wood Surfaces

If your house has wood surfaces, e.g., furniture, doors, and floors when the humidity levels are high, you will undoubtedly see discoloration on the affected areas of the wood. If nothing is done, the wood will later rot. Prolonged exposure to moisture is terrible for anything made of wood as they absorb whatever moisture comes into contact with.

Why Is My House So Humid With The AC On?

If your house feels muggy inside even after running your air conditioning system, multiple factors can cause your HVAC unit not to do its job properly. The reasons below explain why there’s so much humidity in your house.

1. Accumulation of Dirt and Dust

Air filters from time to time tend to accumulate dirt and dust. If no proper maintenance is done, both the indoor and outdoor air conditioner coils accumulate the dirt, inhibiting the unit’s ability to disperse heat into the outdoors, further interfering with the refrigerant cycle.

An interfered refrigerant cycle makes it hard for your AC unit to dehumidify air and do its job properly.

2. Frozen Evaporator Coil

The evaporator coil is best known for its ability to remove heat and humidity from your indoor air. If the airflow is being blocked from going through your air conditioner, or there’s not enough refrigerant flowing through the coil, you will see a layer of ice forming over the evaporator coil.

So when this happens, frozen evaporator coils will no longer extract heat or humidity from the indoor air.

3. Your Current System isn’t Right Size for your House

You need to ensure that your AC system is not too big and, at the same time, it’s not too small for your house. Why so? If your air conditioner is huge, your AC system will run for short cycles resulting in uneven temperatures throughout your house.

On the other hand, if your air conditioner is too small, it will struggle to cool and at the same time dehumidify your house no matter how long it runs.

4. Your Current System is Wearing Out

In most cases, an air conditioner will last ten to fifteen years, so if your air conditioner happens to be more than ten years old, then it’s likely not to control indoor humidity as before. The humidity problem in your house will be due to an old AC system. So the next time you schedule for replacement, be sure to get an air conditioner professional to help you choose one that is best for your home and one that has special humidity controls.

5. The Thermostat Is On The Wrong Setting

Before taking that dial and contacting your HVAC contractor to help you out, be sure to check out your air conditioning settings. Make sure that your AC unit is set to “AUTO” and not “ON.” When the system is left to “ON your AC unit’s fan will run continuously even when the unit is cooling and dehumidifying the air.

But when the setting is left at “AUTO,” your air conditioner will cool and dehumidify air whenever the fan starts to run.


Even if your air conditioner is running as expected, it cannot accommodate increased levels of humidity which may be caused by too many warm bodies inside your house. Too many warm bodies under one roof will cause the air conditioner to have trouble with cooling and dehumidifying at the same time.

The excess moisture from the air caused by the warmth of too many people will generally contribute to the high humidity levels.

7. High Humidity Levels Outside

You need also to observe the outside humidity, especially when your air conditioning system is running, determining the cause of high humidity levels in your house. Even if your AC is running and the humidity outside is high, your house will be affected.

For instance, thunderstorms during a hot day will increase moisture in the air, causing a stick and hot feeling.

8. Cooking Inside

Without proper ventilation, cooking inside your house will cause excess moisture, thus high humidity levels. This is mainly caused by the water evaporating from your stove, and the only way you can prevent this is by cooking while the windows are open to ensure proper humidity control.

How To Reduce Humidity In The House With AC 

Dealing with excess moisture inside your home is not fun at all. High levels of humidity often tamper with the comfort levels of so many homeowners and pose extreme threats to your property as well.

But luckily, below are some of the tips that can help you control indoor humidity in your home.

  • Be sure to line your windows with storm coating or plastic film to eliminate and control moisture and condensation when the air conditioner is running.
  • To avoid peeling paint, be sure to paint your walls rather than using vinyl or wallpapers, which trap moisture inside these ruining the surface of your wall.
  • Always ensure all crawl spaces are properly insulated with a plastic vapor barrier.
  • Ensure your air conditioning system and the climate control system are of the correct size.
  • Since carpets are known for retaining moisture, removing and replacing them with tiles or something else is ideal for ensuring no moisture remains in your home.

Why Is My House So Humid With The AC On FAQs

1. Why is the AC System Cooling but not Removing Humidity?

Your HVAC system can be cooling but not removing humidity due to a leak which may be causing moisture from the air to find its way into your home hence causing high humidity. Another reason that may be causing poor indoor air quality has dirty evaporator coils, which makes it harder for vapor to be wholly absorbed into the coil.

2. Does Running the Fan on My Air Conditioner Reduce Humidity?

Not at all. This is because running the fan will only add heat to your house; thus, adding heat without an air exchange will lower the relative humidity of the air. This means that the room will not be comfortable. Thus you will not get any substantial benefit from the air movement.

3. Why Can’t AC Keep Up With Humidity?

The reason as to why your AC unit is not keeping up with humidity is because your home is poorly ventilated, your air conditioner has clogged air filters, or high seasonal humidity, to name a few reasons. It’s wise to use the tips mentioned above to get the most out of your HVAC system to eliminate this problem.

4. Why Window AC Is Cooling But Not Removing Humidity?

If you happen to have noticed that your air conditioner is not dehumidifying your house, you must have one of the following problems;

  1. Your thermostat fan is set to ON.
  2. Your evaporator coils are dirty, and dust has accumulated in them.
  3. Your air conditioner has a refrigerant leak
  4. Your air conditioner is oversized

5. Why Portable Air Conditioner Increases Humidity?

Your portable air conditioning system increases humidity because of the high humidity in your surroundings. Another reason behind this has dirty air filters, which clog the filters, thus blocking air from coming out of your portable air conditioner.

6. Why Window Air Conditioner Increases Humidity?

Most window air conditioners are intentionally seized and designed to cool the temperatures of a particular seized space and not bring down the humidity to a lower level. Having a window air conditioner that is not seized for your home will increase your AC system’s humidity levels.

Final Thoughts

Well, keeping your home at the proper humidity level can make a huge difference and can help you avoid unnecessary damages to your property. With the information provided above, I believe you now have a clue as to why your house is so humid while the air conditioner running. Be sure to put in place the various tips mentioned above to avoid high humidity levels in your home.