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Do Crawl Space Ventilation Fans Work? (What You Need to Know)

Do Crawl Space Ventilation Fans Work? (What You Need to Know)

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Keeping your house separated from direct contact with the ground beneath is extremely essential to avoid serious issues like earth moisture buildup and flooding, all the while providing a crawl space where you can keep all the essential pipes and cables off the ground.

However, leaving the crawl space without proper ventilation causes moisture buildup, which leads to the formation of mold in your house, which is why ventilation of that space is quite essential. This brings us to today’s question: “do crawl space ventilation fans work?”

Technically speaking, crawl space ventilation fans do work, as they can help in reducing the crawl space moisture buildup by pushing fresh air into the space.

However, they come with many drawbacks that make them not the ideal method to keep your crawl space dry.

In this guide, we’ll show you how crawl space fans work as well as their pros and cons, so you can have a better understanding of this method.

How Do Crawl Space Fans Work?

Before diving into the juicy details of whether crawl space fans are effective or not, let’s first have a quick look at crawl space systems and how the fans work in them.

The crawl space is simply an unoccupied space beneath the house, which acts as a buffer zone to elevate and protect the house from direct contact with the earth.

But since crawl spaces are small, moisture buildup can be a serious issue that causes the formation of mold and mildew, and that’s where crawl space ventilation comes into play!

Crawl spaces are connected to vents that allow the air to circulate in and out. However, the process can be slow, leading to moisture buildup.

To solve that problem, some people use crawl space ventilation fans. These fans will simply blow fresh outside air into the crawl space, allowing the air inside to constantly move, which can slow down moisture buildup.

How Many Crawl Space Fans Do I Need?

The number of fans necessary to provide decent air circulation in your crawl space depends on various aspects, such as:

  1. The level of humidity in your area
  2. The area of the crawl space
  3. Whether you have an insulated crawl space floor
  4. How powerful the crawl space fans are

With that said, there are some numbers that can help you figure out a proper estimate. Since air movement is measured in cubic feet per minute (CFM), you’ll need to calculate the volume of your crawl space to figure that out, which is done by multiplying length x width x height.

For example, if your crawl space dimensions are 50 feet long, 20 feet wide, and 3 feet long, you have a total crawl space volume of 3,000 cubic feet.

Ideally, you want to replace all the air inside the crawl space every 5 minutes. In that case, you need a total fan power of around 600 (3,000/5) CFM

To figure out the number of fans necessary, you should divide the required CFM power by the CFM rating of the fans you have. For example, if your fan has a rating of 200 CFM, you need 3 fans.

With that said, if you’re using conditioned air instead of fans, the numbers are completely different.

According to the EPA’s current Indoor Policy Record, you need around 1 (CFM) cubic feet per minute of conditioned air for every 50 square feet of floor area to provide a good circulation of air.

What Are the Advantages of Using Crawl Space Fans?

Using crawl space fans comes with a couple of essential benefits. Let’s have a quick look at them:

They’re Affordable and Easy to Use

Crawl space fans are relatively affordable when compared to other methods of ventilation. A typical crawl space ventilation fan with a rating of 100 to 150 CFM should cost you anywhere between $90 to $120.

All you need to do is install these fans at the crawl space vents and you’re good to go.

They Improve Air Circulation Inside the Crawl Space

If you only use crawl space vents to circulate air in and out, you’re relying on a passive current that is remarkably slow.

In that case, if the moisture buildup rate is pretty high, humidity levels inside the crawl space will increase.

This increases the risk of mold infestation that can damage the foundations of your household and cost you a lot of money to repair.

If you use crawl space fans, you’ll achieve active air circulation by pushing fresh outside air into the crawl space, which reduces the internal humidity levels (provided that humidity levels outside are lower).

What Are the Downsides of Using Crawl Space Fans?

Although crawl space fans work, they’re not the ideal solution when it comes to ventilation. Here’s a quick look at some of the downsides of using them:

Creates a Stack Effect

The stack effect is a phenomenon caused by the movement of air through unsealed openings. In that case, the outside air enters the crawl space through the fans then it gets pushed up towards the house and out through the attic.

Even if the humidity level is reduced by introducing new air, the hot air will continue to rise up, causing water vapor to come in contact with the house foundations.

This will eventually lead to an increased risk of mold, defeating the purpose of using the fans.

Can Be a Gateway to Pest Infestations

In order to use the fan, you’ll need a constantly open vent that leads to the outside. Even the smallest spaces are enough for many pests to find their way inside your house, such as insects, rodents, and even small snakes if they live around your area!

Doesn’t Protect the Crawl Space from Water Damage

While crawl space fans might seem like a solution to moisture and lack of ventilation, they don’t protect your crawl space from floods. If water finds its way into your crawl space, it can cause massive, costly damage!

Reduces the Efficiency of Heating and Cooling in the House

As previously discussed, the stack effect will cause the outside to flow through your house. If you have allergies and use an HVAC system in your house to purify the air, crawl space vents will dramatically reduce its efficiency.

Similarly, heating and cooling bills will be noticeably high because it would require more energy to adjust room temperature with the outside air constantly counteracting your heating or cooling system.

What Is the Most Effective Method to Keep the Crawl Space Dry?

Based on all the previously mentioned drawbacks, you can see why these fans aren’t the best method to prevent moisture buildup in your crawl space.

Instead, the best method to keep it dry is by using crawl space encapsulation. This one works by sealing the floor, walls, and the ceiling of the crawl space with vapor barriers, then installing a dehumidifier to keep the moisture levels under control.

Final Thoughts

This wraps it up for today’s guide that walks you through everything you need to know about crawl space ventilation and fans.

As you can see, crawl space fans do work when they’re compared to passive crawl space ventilation.

However, using fans for crawl space ventilation comes with various drawbacks that can do more harm than good in some situations.

On the other hand, encapsulation by sealing the crawl space and installing moisture barriers and dehumidifiers remains the best possible method to prevent moisture buildup in your household.


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