Does Outdoor Humidity Affect Indoor Humidity? You’ll Be Surprised!

Liz Yang

Indoor humidity has a significant impact on your health and the condition of your house, even more than you expect. The indoor humidity that is too high or too low can wreak havoc. 

We often come across a situation where we feel much more comfortable when we go outside than indoors or vice versa. This makes many people wonder if outdoor humidity really affects indoor humidity.

Yes, outdoor humidity has an impact on indoor humidity. The moisture, along with the air, will get in and out of the house through windows, doors, and other crevices. There are many ways you can employ to increase or decrease the effect of outdoor humidity on indoor humidity.

In this post, I will walk you through the relationship between each other and guide you on how to combat the effect of outdoor humidity on indoor humidity. You will get many helpful tips on maintaining a comfortable environment at home. 

Without further ado, let’s start!

Why can outdoor humidity affect indoor humidity?

We like to go outside and take a deep breath when we are bored inside. The outdoor air seems to be different from what we inhale in the room. However, it doesn’t mean that outdoor humidity has no effect on the indoor environment.

The outdoor air will get into the room through the window gaps, door cracks, and other crevices. When you open and close the door, the air will also sneak into your room as well. As an important air component, moisture particles will also enter the room.

As a result, outdoor humidity will always play a role in affecting indoor humidity. The effect can be large or small depending on a variety of factors. (More on that later)

What effect does outdoor humidity have on indoor humidity?

effect of outdoor humidity on indoor humidity

The ideal range of indoor humidity is about 30% to 50% or 35% to 55% according to different sources and the 45% seems to be the sweet spot.

When the indoor air is dry, it will result in dry skin, sore throats, allergies, and many other ailments. The wood will start to shrink, and the static electricity can cause fires.

High indoor humidity can lead to many adverse effects too. The dust mites and mold spores will thrive, and the wood will warp and split. 

Therefore, keeping your house or office at a comfortable humidity level is crucial for your well-being and property.

While you can use your HVAC system to regulate indoor humidity, taking advantage of outdoor humidity is also a good option. After all, this method will not cost you anything.

In the winter months, the air is dryer because the air is not capable of holding so much water when the temperature goes down.

However, indoor humidity can reduce even significantly when the moisture in the air remains the same. This is due to the heating system raising the room temperature and sucking up the water, causing the relative humidity to drop even further.

In this case, you can open the windows to allow the outdoor air to disperse in the house, freshen the air and increase the indoor humidity. 

On top of it, when indoor humidity is higher than outdoor humidity due to the use of the bathroom and kitchen and human perspiration, it can also help to lower the humidity indoors.

However, outdoor humidity can also do harm to your house. 

It is not unusual to see molds present on the wall on rainy days or in summer. In these conditions, the outside humidity will be extremely high. If you continue to open windows and doors, excess moisture will enter the room, worsening the situation.

Hence, depending on the climate and how you control it, outdoor humidity can both positively and negatively affect indoor humidity.

Ways to remedy the effect of outdoor humidity on indoor humidity?

To increase the effect of outdoor humidity, you can just open your windows and doors as more as you can. But it is not as simple to reduce the impact as it appears.

Seal the gaps and cracks

As we mentioned earlier, gaps and cracks are the main culprits. If you notice that your indoor humidity is much higher or lower than other houses or rooms, you should inspect the state of windows and doors. Sealing the gaps and cracks can keep the outside air out of your house.

Use a humidifier

When the indoor humidity level is low, you can use a room humidifier or whole-house humidifier to improve the condition. Some advanced models feature a humidistat which can turn off when the targeted humidity level is reached. 

Use a dehumidifier

When the outside air is too damp, you can use a dehumidifier to extract the extra moisture in the room. In addition, a dehumidifier is a helpful piece of equipment in the basement and crawl space which is more damper than other places. 

You may need to run it several times per day to keep the dampness at bay.

Turn on your air conditioner

Similar to dehumidifiers, air conditioners can take away the excess moisture in the room, which can counteract the humidity coming from the outside. 

Install a ventilation fan 

For those who don’t have a window in the bathroom or kitchen, installing a ventilation fan is necessary.

The water vapor produced by a shower or bath can remain in the room for an extended period of time, increasing humidity and promoting the growth of bacteria and mold. The ventilation fan aids in the removal of moisture particles, keeping the closed area in good condition.

Wrapping up

Outdoor humidity can affect indoor humidity because air can always find its way to get into the building. 

Sometimes, outdoor humidity can have a positive impact on the indoor environment. For example, opening the window in winter can bring some desired moisture to the room every so often. However, the excessive moisture outside can foster the growth of germs indoors on summer or rainy days. 

Thanks to technological advancement, you can mitigate the effect in many ways. Humidifiers, dehumidifiers, ACs, and fans are also effective. 

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 a lot 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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