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Dryer Venting Under the House | Potential Problems

Venting your dryer tends to require some extra effort as you will need to comply with certain building codes in order to abide by health and safety protocols. To do so, you might have to make some holes in your walls in order to vent your appliance properly – hence the extra effort.

Some might think that if their dryer is in the basement, then it will be easier to vent it directly under the house. However much effort this saves you at first, the numerous issues from doing so will eventually catch up with you – and they won’t come cheap.


Venting a dryer under a house can increase humidity and lower the air quality throughout the whole house. It will likely cause mold and mildew growth, which can lead to structural damage or serious health issues. It can decrease the effectiveness of wall insulation and cause pest infestation or fire.

What Do Building Codes Say About Venting Dryers?

In order to ensure the health and safety of you and your family, whatever additions or changes you bring to your home have to comply with certain building codes.

These codes are created to ensure that individuals do not mess with the structural integrity of their homes, or do things that might be of danger to them.

When it comes to venting appliances in general, the International Residential Code (IRC) Section M1501.1 explains that exhaust systems, in general, need to be directed to the outside of the home. It specifically prohibits venting into the crawl space (the area under the house).

prohibits venting into the crawl space (the area under the house

Another section of the code, Section M1502 revolves specifically around venting dryers. In Section M1502.2, it states that:

“Dryer exhaust systems shall be independent of all other systems and shall convey the moisture to the outdoors.”

But Section M1502.1 states that dryers need to be vented in accordance with the manufacturers’ instructions. Typically, these take precedent over the codes as long as the dryer meets minimum industry standards.

So, let’s look at a couple of examples of what manufacturers have to say about venting the dryer under the house.

You can clearly see on this Amana Clothes’ Dryer manual that there is a huge warning that tells the user that the dryer must be vented outside, and cannot be vented into any gas vent, chimney, attic, or crawl space.

Similarly, the gas Alliance Speed Queen dryer also requires the user to vent the dryer directly outdoors and again prohibits venting into a crawl space or any other closed-off space in the home.

It seems that everyone agrees that dryers need to be vented outside, and there are good reasons for that.

Possible Problems of Venting Dryer Under the House

Mold and Mildew Issues

Dryers need to be vented outside so that the moisture inside the dryer can be dissipated outdoors and away from the house.

If you vent your dryer underneath your house, this moisture will accumulate and create a potential breeding ground for mold and mildew to grow.

shocked man seeing mold and mildew

This is because mold spores exist in the air, and when there is a surface with moisture, it attracts the spores and causes them to settle and grow into unsightly and harmful patches of mold.

Exposure to mold and mildew can have negative effects on the health of you and your family. You can experience symptoms ranging from mild allergy-like symptoms to more severe ones, such as severe headaches, loss of hair, and even loss of consciousness.

Structural Damage

Not only will mold cause potentially dangerous health issues, but it can also affect the structural integrity of your home.

If mold grows beneath the house, it can cause the foundation of your home to become weak and brittle, which can have disastrous results for your family’s safety.

Additionally, the excess moisture can also cause the wood to rot. Considering the fact that most of the structures below the house are designed to keep the entire structure standing, this is not good! Furthermore, since this rotting wood is underneath your home, the rot could spread to the floors above.

If you are venting your dryer under your house, then you are creating a large possible area for water to accumulate, thereby increasing the possibility of rot spreading throughout your home.

Your floors can become extremely brittle, making it easy for you to fall through if the damage goes unnoticed.

Potential Fire Hazard

The excess moisture will cause a variety of health and structural issues; however, the hot air exhausted from the dryer doesn’t contain only moisture but lint as well.

Lint is highly flammable, and so when it accumulates (together with dust) in the crawlspace, it presents a fire hazard. Research shows that thousands of Americans have reported a house fire caused by dryer lint.

fireman fighting a raging fire with big flames

The lint can be easily ignited by the heating elements from your dryer. Now, if a fire were to start underneath your home, it might take longer to discover it, which could have catastrophic results.

It Can Put Extra Load on the HVAC System

When venting your dryer underneath your home, you increase the amount of moisture and heat in the air and, therefore, the degree of humidity.

When there is moisture surrounding the components of your HVAC system, you can expect your insulation to become damaged. Insulation needs to be completely dry in order for it to work optimally.

If water gets into the insulation, it affects how much heat is gained and transferred throughout the house. This means that your HVAC will be working extra hard to get warmth dispersed throughout the home, which can seriously rack up your energy bill.

In winter, this can become seriously expensive when you are trying to keep out the cold and make the home nice and toasty.

High Humidity in the House

The dryer will release hot, moist air into your crawl space. This not only increases humidity levels in that particular area, but the humidity can spread to the rest of the house.

When the humidity levels are high in your home, you increase the presence of harmful chemicals that are in the air. You can start to experience uncomfortable respiratory illnesses.

Dust mites and particles will also be carried by this moist air, which can make the air difficult to breathe in or cause allergies. Not to mention, it can also damage your décor and make the whole house feel stuffy.

Pest Infestation

Another consequence of venting your dryer under your house is that you can attract pests that thrive in the warm, humid environment that the expelled hot air creates.

Dust mites, silverfish, and mold mites are common pests that you will find in any humid area of your home. But you can also get the bigger critters like mice and rats. These pests will start to breed, and soon enough, you will have a massive infestation on your hands.

You’ll keep finding tiny (or not so tiny) pests in all areas of your home as the humidity spreads. Don’t forget all the damage that they can do and the diseases that they carry. Eventually, you will be left with no choice but to fork over the cash for an exterminator.

However, until you actually address the underlying cause of this issue, the bugs will just keep coming back.

Gas Dryers Should Always Be Vented Outside

One dryer that definitely cannot be vented underneath your house is a gas dryer.

These dryers present the added danger of carbon monoxide leaks and are, therefore, recommended to only be vented directly outside.

vent directly outside of house. ventilation near window

You need to be able to get the gas as far away from humans as possible, so venting the dryer outdoors allows the air and wind to disperse the gas.

Carbon monoxide is a gas that is tasteless, colorless, and odorless. It can cause a variety of health issues. You often don’t realize you’ve got carbon monoxide poisoning until it’s too late, and you are rushed to the emergency with seemingly unexplainable symptoms.

illustration of Symptoms of Carbon Monoxide Poisoning

Consider Getting a Ventless Dryer

If you simply can’t vent the dryer directly outside (maybe you’re renting and can’t make any holes in the walls), it might be best to buy a ventless dryer.

Ventless dryers are great because they do not need to be vented at all. The hot air that is circulated during the cycle is cooled and converted to water, which then accumulates in a reservoir that needs to be emptied regularly.

As long as you still have some ventilation (such as leaving a door or window open) in the space the dryer is in, the risk of moisture and humidity problems in your home is minimal. These dryers also tend to use less energy, so they will cost you less to run month to month.

Sources

https://www.erieinsurance.com/blog/how-to-prevent-a-dryer-fire

https://www.cdc.gov/mold/faqs.htm

https://apexpestcontrolwnc.com/bugs-attracted-to-moisture/

https://extension.missouri.edu/publications/gh5928#:~:text=Mold%20spores%20are%20present%20in,or%20additional%20insulation%20are%20needed.

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