Skip to Content

Can Crawl Space Humidity Be Too Low?

Can Crawl Space Humidity Be Too Low?

Share this post:

This post may contain affiliate links. If you click an affiliate link and make a purchase, I may earn a commission. Also, as an Amazon Associate I earn from qualifying purchases.

A crawl space is a hallowed, unoccupied area beneath the first floor of a building. Typically, it’s only around 3 feet high. That’s enough for a person to crawl in it, hence the name.

The crawl space is a convenient area to install HVAC units, piping systems, plumbing systems, and electrical wiring. If moisture accumulates in your crawl space, it can damage some systems installed there.

Also, humidity can cause many dangerous problems like mold and wood rot. So, it’s essential that the crawl space remains dry and free of moisture to avoid having any issues.

That can make you wonder; can crawl space humidity be too low? Will it be as harmful as high humidity?

The answer is yes! However, you don’t need to worry, as in today’s article, we’ll tell you everything you need to know about crawl space humidity. Let’s dive in.

What Percent Humidity Should My Crawl Space Be?

First and foremost, we need to understand what relative humidity is. Humidity is the amount of water in the air.

On the other hand, relative humidity is the amount of water content suspended in the air relative to the maximum amount of water that can be in the air at a certain temperature.

In other words, the higher the temperature, the more water vapor the air will be able to hold. The relative humidity is what we need to measure in your crawl space.

Measuring the humidity levels in your crawl space can be done using a digital hygrometer. Typically, you want the humidity level to be between 30-60% to avoid any problems. To be more precise, the ideal humidity level should be around 45 to 55 %.

Can Crawl Space Humidity Be Too Low?

The simple answer is yes. If the relative humidity in your crawl space becomes lower than 25%, that can be considered too low. Just like high humidity can cause damage to your house, low humidity is dangerous too.

To elaborate, if the moisture inside your wood becomes lower than 5%, the wood will dry out, shrink, and become weaker. That can lead to structural damage.

To keep the moisture in the wood between 5-12%, we need to adjust the crawl space humidity to 30-50%.

Moreover, your crawl space needs a certain amount of moisture and humidity. Too high or too low humidity can cause damage to your crawl space and your entire building.

So, you need to keep track of the humidity levels in your crawl space. That’s why having a crawl space dehumidifier system is essential.

A dehumidifier is an appliance that takes humidity from the air. Typically, dehumidifiers contain a fan that draws in hot air, which is met by cold coils. So, the moisture in the air turns into water. Finally, the water is disposed of through a drainpipe.

What Happens if the Crawl Space Humidity Becomes Too Low?

Around 40% of the air that goes into your house comes from the crawl space. So, a dry crawl space can cause many structural problems and even health problems for the residents of the house.

If your crawl space humidity is too low, it can cause dry rot. Additionally, many types of viruses and harmful bacteria can survive low humidity levels and affect the health of the household residents.

Similarly, if the humidity is high in your crawl space, it will cause mold and mildew to grow. It might even cause pest or rodent infestation.

What Size Dehumidifier Do I Need for My Crawl Space?

Dehumidifiers come in different sizes. You need to pick a suitable dehumidifier according to the size of your crawl space. In other words, if you have a small crawl space, you’ll need to choose a small dehumidifier.

The general rule of thumb is that for a 300-square-foot crawl space, you’ll need to pick a 20-pint or 30-pint dehumidifier. For a bigger crawl space that’s about 500 square feet (46.45 m²), you’ll want a 25-40-pint dehumidifier.

Moreover, if your crawl space is about 800 square feet (74.32 m²), you’ll need a 35-50-pint dehumidifier. For a 1,200-square-foot crawl space, you should get a 50-60-pint dehumidifier.

Where to Place Dehumidifier in Crawl Space

After picking the right size of a dehumidifier, you need to consider where you’ll be placing it. While it might not seem like a huge deal, the placement of the dehumidifier inside your crawl space is extremely important.

The best place for a dehumidifier in your crawl space is where the discharged airflow isn’t blocked. Ideally, we want the dehumidifier to exchange as much air as possible.

If your crawl space has tight areas where the dehumidifier won’t be able to reach, it might be a good idea to add a fan. The fan allows the air to circulate more around the crawl space. That leads to better air circulation and more humid air reaching the dehumidifier.

You can also place it in a spot that has extra high humidity. It’s critical to keep an eye out for the source of humidity. Placing the dehumidifier near the source of humidity can make a significant difference and reduce the risks of mold.

You’ll also need to consider the draining process when you’re picking the location. You want the draining process to run smoothly.

One thing worth mentioning is that dehumidifiers can be a little noisy. So, make sure to pick a place where noise won’t be leaking to the top floors.

Where to Drain Dehumidifier in Crawl Space

There are two methods used for crawl space dehumidifier drainage; the gravity drains system and the condensate pump system.

First and foremost, you need to make sure that the termination process occurs at least 24 inches away from the foundation and on a slope.

For any draining method you choose, you’ll need to make sure that the drain pipe is working efficiently.

The Gravity Drains System

This method is used to transfer the condensation away from the dehumidifier. It needs a certain drop from the dehumidifier to work, hence the name. The general rule of thumb is ¼ inch of drop for every 10 feet of run.

The Condensate Pumps

The condensate pumps act as a reservoir for collecting the condensate. Once it’s all filled up, the water will be forced through a drainpipe.

How Does the Drainpipe Affect the Dehumidifier?

The main function of the dehumidifier is to get rid of the moisture in the air. So, without proper drainage, it’ll be doing more harm than good.

First, you’ll need a drainpipe that’s made from high-quality material, like PEX, PVC, or CPVC. Next, depending on the size of the drainpipe you’ll be using, you’ll need to drill a hole through the foundation for the drainpipe to pass through.


Do you still have a question in mind? Here are some frequently asked questions regarding our topic for today.

What is the acceptable moisture level in the crawl space?

Ideally, you want the crawl space wood moisture content to be around 10-15%. It’s crucial that the moisture level doesn’t become too high or too low, as it can cause structural damage.

What moisture level allows for the formation and growth of mold?

Mold begins to grow at humidity levels of 55% and higher. So, it’s crucial to keep humidity levels at 45% to 55%.

Final Thoughts

The humidity level in your crawl space should always be around 45% to 55%. If the humidity becomes too high, it might cause mold and mildew to grow.

Can crawl space humidity be too low? The answer is yes. You need to monitor the humidity level and keep it at the ideal level. A dry crawl space can be as dangerous as a humid one.

Not only will it cause structural damage to your house, but it also can cause various health issues for the residents of the household. So, don’t let the crawl space humidity become too high or too low. Stay safe!


If you want more backyard tips including recipes, how-tos and more, make sure you subscribe to my youtube channel

Share this post: