Does Opening Windows Increase Humidity?

If you live in a humid climate, keeping comfortable is about more than controlling the temperature inside your home. You also have to find a way to deal with the relentless moisture in the air.

When the humidity inside the home becomes too much to handle, many homeowners wonder if opening the window would help the issue or make it worse. In this article, we’ll answer the question ‘does opening windows increase humidity?’ by taking an in-depth look at how moisture in the air behaves at different temperatures and how opening windows can drive that moisture up or down.

a woman opening the window to increase humidity

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Will Opening Windows Increase Humidity Inside?

As you can imagine, this answer very much depends on the conditions inside and outside your home.

If you live in a dry climate with constant low humidity outdoors, then the answer is pretty straightforward. Cooking, taking showers, watering plants, and running the dishwasher will all increase the humidity inside. So long as it isn’t raining or foggy outside, you can be certain that opening the windows in dry climates will help reduce the humidity levels inside.

But in humid climates, the answer is much less straightforward. Even looking at a hygrometer is unlikely to help you find the answer in these environments. At least, not without doing some math first.

Why? Because of the difference between relative and absolute humidity.

Relative vs. Absolute Humidity

Relative humidity is the amount of water in the air relative to how much water the air could hold at its current temperature. This type of humidity is expressed as a percentage and is the most common measure of humidity.

On the other hand, absolute humidity is the volume of water vapor in the air. This measurement is not based on temperature and is expressed as grams of moisture per cubic meter.

When determining if there is more moisture inside your home than outside, you need to convert relative humidity to absolute. Once the air outside comes inside, its temperature will change to match what is in your home. What won’t change is the amount of moisture coming in with that air.

For example, let’s say it’s 70 degrees and 50% humidity inside and 80 degrees and 40% humidity outside. In absolute terms, the humidity level inside is actually lower than outside. This means that if you were to open the window, you would only be letting more humidity into your home.

You can play around with different calculations using this humidity calculator.

The Role of the AC

a person using the remote to set the AC’s temperature

If you live in a humid environment and your home is cooler than the outside, you can expect the moisture level outside to be greater than what it is inside. This means opening the windows to reduce the humidity inside is not going to work.

If you have the AC running to help keep your house cool, then you definitely want to keep your windows closed.

We’ve talked before about how cracking the windows with the AC on is not a good idea. But when it comes to battling humidity, there is another good reason not to open the windows.

As your AC draws in warm air, the cooling coils in the unit cause moisture in that air to condense. This water vapor accumulates on the coils and drips down into the condensation pan, where it drains out of your home. In this way, your AC will help dehumidify your home.

But for this to work at a detectable level, you need to keep the windows closed so more humidity is not being sucked in.

Using a Dehumidifier

A cat standing next to a dehumidifier

While AC units do remove some moisture from the air, this effect is minimal at best. If you want to remove that sweltering humidity from your home, you need a dehumidifier.

If your house has a central HVAC system and humidity is a problem in every room, then getting a whole-house dehumidifier is a great idea. These large units connect to your central heating and cooling system to pull humidity out of the air as your AC runs.

If you do not have central AC or humidity is a problem only in certain rooms of the house, then a stand-alone dehumidifier is a good choice. You can get a portable mini dehumidifier or a large-capacity dehumidifier for basements and crawl spaces.

Bottom Line: Be Cautious About Opening Windows

If you live in a dry climate, opening the windows can help remove humidity from your home. But, if you live in a humid environment, opening the windows is only likely to bring more moisture in. This is often true even when the relative humidity outside is lower than what it is inside.

If you live in a humid climate, your best bet for battling humidity is to keep the windows closed, the AC running, and use a dehumidifier.

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