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Do Crawl Space Ventilation Fans Work?

Crawl spaces and low-ceiling areas are home to various pests, fungi, bacteria, mold, and termites. Excessive moisture and humidity make it a perfect place for them to live. Hence it should be kept properly ventilated otherwise it may eventually be devastating to the overall health of the building.

The right system of ventilation is therefore crucial. A lot of novice builders rely on fans to ventilate such spaces inside the building. So, let us find out do crawl space ventilation fans work or if it is just a failed idea.

Crawl spaces often remain a hidden and often overlooked area in homes, yet they play a crucial role in maintaining the structural integrity and indoor air quality of a house. Crawl space ventilation fans are used for crawl space maintenance, aiding in moisture control and preventing potential issues like mold growth, wood rot, and poor air quality.

What is Crawl Space in a House?

A crawl space in a house is a shallow and accessible area beneath the main living area, typically between the ground and the first floor. It is usually used in homes that do not have a full basement. The crawl space provides access to plumbing, electrical systems, and other utilities, allowing maintenance and repairs to be performed. It also helps with ventilation and can serve as an insulating buffer between the ground and the living space above. However, crawl spaces can sometimes be prone to moisture issues, pests, and inadequate insulation if not properly maintained or designed.

crawl space

What is a Crawl Space Ventilation Fan?

I think a very less percentage of people are bothered about crawl space ventilation and completely rely on the builder or contractor for the solution. But it has a big impact on the entire building’s health. Every building owner should know how much ventilation does a crawl space need and how to remove humidity from the crawl space.

Crawl space fans are the vent fans installed on the walls. Its basic functionality is to blow the outside air into the crawl space so that to keep it dry and humidity free. It will also reduce the level of water accumulation inside such spaces. Excessive moisture concerns are also resolved.

Crawl spaces are typically found beneath homes that lack a full basement or are built on a raised foundation. These areas are susceptible to moisture buildup due to factors such as groundwater seepage, humidity, and inadequate ventilation. Excess moisture in crawl spaces can lead to a range of problems, including the growth of mold and mildew, deterioration of wooden structures, and the release of musty odors into the living space above.

Do Crawl Space Ventilation Fans Work?

No, crawl space ventilation fans do not work effectively. Although it may work fine sometimes it is not effective for the purpose they are installed. Instead, such vent fans are ruinous for the healthy air of your house. Crawl space ventilation fans create a lot of water accumulation, humidity, moisture, and temperature problems (Further in this article it is explained in detail). Plus, it can provide a comfy place for pests, insects, molds, termites, and fungi due to moisture and humidity levels.

As per the users who have used crawl space fans, it seems these fans don’t work effectively, but a company ATMOX commits that their crawl space fans work well.

crawl space fan

Actually, the idea behind installing the crawl space ventilation fan is to cycle the air outside the crawl space, reducing the level of humidity and keeping the air inside the crawl space cool and dry. But it doesn’t happen likewise.

Crawl space ventilation fans are specifically designed to address these moisture-related concerns. These fans work by actively exchanging air between the crawl space and the outdoor environment. The idea is to create a continuous flow of air, help in regulating humidity levels, prevent stagnation, and reduce the likelihood of moisture buildup.

Crawl space ventilation fans operate on a simple principle: air movement. They are typically installed in the crawl space walls or foundation vents. These fans can be either exhaust fans, which expel air from the crawl space, or supply fans, which bring fresh outdoor air into the crawl space. Some systems combine both types of fans to achieve optimal airflow.

Exhaust fans work by drawing out damp, humid air from the crawl space and expelling it outside. This helps remove excess moisture and reduce the risk of mold and mildew growth. Supply fans, on the other hand, bring fresh, drier air into the crawl space, helping to maintain a balanced humidity level and preventing the buildup of stagnant, moist air.

But crawl space ventilation fans fail to control the appropriate level of moisture and humidity. The primary cause for this failure of the crawl space ventilation fan is the vent opening.

Should I Close The Crawl Space Vents?

Now let us do some temperature and humidity math to find out should crawl space vents be open or should I close the crawl space vents in my house or office building.

Say on a hot day in any city in the U.S., the temperature inside the crawl space is around 65°F,  and 95°F outside the space. The outside air comes in contact with inside air through the crawl space vent.

Now if you don’t know, let me educate you that the level of humidity increases by 2.2% with each degree of air that cools. Taking this fact into account, you can calculate that the level of humidity will always go up through crawl space fans. Eventually, when inside the crawl space relative humidity levels go up, and condensation starts on the wall or pipes or the floor. This marks the beginning of damage to the crawl space.

So, should crawl space vents be open? NO, open crawl space vents may add to your problems. Continue reading to know how…

Problems With Open Crawl Space Vents

Here I like to catch your attention to some of the concerns that people often ignore regarding the open crawl space vents.

Moisture Level

Open crawl space vents invite moisture in. This is the most obvious concern with crawl space vents. Due to different air temperatures inside and outside the building, the level of humidity keeps on changing. The level of moisture in the crawl space must be very low, otherwise, it provides an ideal space for molds and mildews. Moreover, 

Way To Water Come Inside

In the rainy season, rainwater can easily enter through the open crawl space vent area. This eventually raises the moisture percentage in the air. In some buildings, there is an option to cover the open vents or close them. But it has been seen that water comes in anyway. Building construction experts suggest the ultimate solution is to permanently close the crawl space vents.

Way To Pests

Open crawl vents are the perfect door for pests. The temperature inside the crawl space is loved by the pests and they can manage to enter even from a small and thin opening. Ants, mosquitos, and small snakes can easily find their way in through open crawl vents.

Costs Higher Energy Bills

According to a survey made by a local agency, it has been observed that houses where crawl space has open vents consume more energy. Open crawl space vents are not energy efficient. From the vents, the heating and cooling of your house go outside.

Stack Effect Deteriorates Air Quality

The stack effect is applied when air enters the house from the crawl space and exits from the attic under the roof. When air enters through an open crawl space vent, it warms up and rises. Then it goes out of the attic. This process continues.

The stack effect is not good. It damages the quality of the air you are breathing in your house. Let me tell you how. When air enters the crawl space from an open vent area, it causes moisture too. This will give birth to unwanted molds and fungi. Therefore airborne droppings of molds and insects and outside air pollutants travel to your entire house through the air.

Fixing Open Crawl Space Ventilation (Alternatives to Crawl Space Fans)

Alright! We have now valid reasons and logic to believe that crawl space ventilation fans do not work effectively. So, what is the solution then?

Different factors come into the picture, say, year of construction, location, and temperature. The first and foremost thing you need to do is shut the ventilation space. To do this, you may consult industry experts and professionals. They have hands-on knowledge and updated techniques to get it done perfectly. To fix open crawl space vents, the following services are usually added.

  • Vent Covers
  • Crawl space insulation
  • Install Vapor barriers
  • Installing Dehumidifiers
  • Crawl space waterproofing system. (Recommended in severe cases of water issues and moisture)

Installing Dehumidifiers

The job of dehumidifiers is to reduce the level of humidity in the room. Installing any dehumidifier is very simple. It can be hooked up to the circuit breaker or you may also set up a temporary unit for it.

Install Vapor Barriers

A vapor barrier is the easiest way to keep moisture away from wood beams and foundations. If your house has wood designs and set up, vapor barriers are for you. In case of flood,  vapor barriers will not let the water touch the wood beams.

Use Vacuums To Dry water

You may easily buy or rent a wet-dry vacuum to suck up all the excess water deposits in the crawl space. If the water deposit is huge,  you may rent a big-size vacuum machine usually used in industries. Appoint a professional to do the job better and easy for you.

Sump Pump

In areas prone to flooding or excess groundwater, a sump pump can be installed to remove water from the crawl space.

Professional Assessment

It’s a good idea to consult with a professional specializing in crawl space solutions to assess your specific situation and recommend the best course of action.

Is The Crawl Space Safe in a Tornado?

People living in low-lying areas are often concerned about whether the crawl space is safe in a Tornado. Well, it counts on certain factors like the location and architecture of the building. Various other factors are involved. All in all, what is important is that the ventilation system of the building must be proper. It ensures that there leaves no traces of moisture and humidity.


Crawl spaces are not just useless empty spaces in your building. They equipped and protected the plumbing and electrical work underneath. Without proper ventilation and failing to keep the crawl space dry,  you may attract molds, insects, and fungi. This may eventually lead to damaging the entire building. A crawl space ventilation fan is not a full-proof way to keep the moisture and humidity out of the crawl space. Altogether, regular inspection, proper installation, and appropriate selection of ventilation methods can collectively contribute to a well-ventilated and moisture-controlled crawl space, ultimately benefiting the entire home.

About the author

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Niki D.

Niki D. is proficient in handling issues related to ACs, fans, air purifiers and other home environment controlling machines. Through this website she is sharing her experience and understanding of latest technology and trends in home climate control.

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