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Dryer Vent Termination Requirements

If you are researching the installation of a dryer in your home, you probably know that there are a lot of rules to follow. The terminal point of your dryer vent is no different, and for good reasons.

While the termination of your dryer vent may seem like the most inconsequential part of the installation process, it is essential to your dryer’s function. The opening at the end of the vent must be the correct size and in an appropriate location.

Dryer exhaust vents must terminate outdoors according to manufacturer/IRC specifications (along with any local regulations). The terminal point must be the same size as the rest of the vent and must be equipped with a backdraft damper. For safety reasons, screens are prohibited.

Outdoor Termination is Required

The building code regulates most of the dryer installation, and dryer vent requirements are no different, especially the for the vent terminal. The International Residential Code (IRC), Section M1502.3, requires that exhaust ducts for dryers terminate directly to the outdoors.

Exhaust air contains unwanted substances and odors you don’t want to be released into your home or interfere with indoor air quality. When it comes to dryer vents, they are exhausting humidity, lint, VOCs, and combustion byproducts (in the case of gas dryers).

Humidity causes issues like mold, mildew, and water damage within your home. Lint is highly flammable, so it must be cleared away from the dryer and the heat it produces. VOCs are harmful to health, and combustion byproducts can be deadly.

How you vent outdoors is also important. For example, you cannot vent the dryer through a chimney.

Lint collected in the lint trap and lint collected in vent are flammable

The only circumstance where you do not need to vent a dryer is if it is listed for ventless installation (Section M1502.2). Ventless dryers are exempt from this regulation because of how they deal with moisture and lint.

What Happens if You Don’t Use a Dryer Vent

Manufacturer Specifications Take Priority

The manufacturer’s instructions for where and how the vent must terminate take precedence (IRC Section M1502.3).

The IRC gives dryer manufacturers authority for the dryer duct dimensions and location. The caveat for approval of the installation instructions is that the product must be listed and approved.

Being listed refers to the rating (generally a UL or ANSI) code given to a product by an organization that regulates safety and performance.

The listing mentioned in the building code shows that the IRC approves of the standards for testing, meaning you can rely on the instructions to be safe.

This is also credible for inspections and insurance claims; you may just need to provide the installation manual.

If your product doesn’t come with instructions, you can always use the alternative instructions given by the IRC.

Location If Not Specified by Manufacturer

Since safety is crucial when it comes to dryer vents, a lack of information from the product manuals does not mean that you are without recourse.

If you find yourself without instructions from the manufacturer to follow for the duct termination, the IRC does provide its own instructions in Section M1502.3.

When there are no specifications from the manufacturer, the IRC dictates the vent must terminate at least 3′ (914 mm) from any openings to the building (including those in ventilated soffits) and have a damper.

According to statistics from the National Fire Protection Association (2020), clothes dryers are responsible for 4% of structural house fires. A third of those resulted from a failure to clean the dryer vent, and 27% of that is attributed to the ignition of lint.

When lint is not dealt with appropriately, it becomes dangerous. Therefore, dryer vents must be a certain distance from openings to allow lint to exhaust properly and prevent it from blowing into your home or HVAC system, where it can potentially start fires.

In addition, the lint can start blocking the vent, leading to heat buildups, which exacerbates the fire risk.

Dryers can even be vented through the floor if allowed by the manufacturer of if doing so does not contravene any other termination requirements set out in the IRC.

Backdraft Dampers Are Mandatory

Dryer exhaust vents must be fitted with a backdraft damper (Section M1502.3). These devices are essential for any exhaust vent, not just the dryer, which is why I have an entire all-you-need-to-know guide.

Backdraft dampers typically connect to the end of a duct run (either at the terminal or where the ducting connects to the central vent in apartment buildings) and are designed to keep airflow unidirectional.

AC Infinity 6" Backdraft Damper, One-Way Airflow Ducting Insert with Spring-Loaded Folding Blades for 6” Ducting in Range Hoods and Bathrooms Fans

Even when venting the dryer through a soffit, a damper is necessary. Air is allowed out of the vent while preventing backflow, meaning that what is exhausted stays out.

The air in the vent is also a different temperature to the air outside. Air from the dryer is hot and humid from the drying process. The backdraft damper prevents the dryer and outdoor air from mixing inside the vent, minimizing condensation that occurs with the humid air is cooled.

Screens are Prohibited

You mustn’t install a screen at the termination point, according to Section M1502.3 of the IRC.

Screens are a good way to prevent debris, insects, and animals from getting caught or cozy in your vent terminal. However, you should remove a screen attached to any dryer vent because of what it exhausts: lint.

If you have a screen attached to the vent’s opening, you will end up with lint catching on the mesh and building up.

Firstly, this can clog the vent and prevent proper airflow. This means your exhaust isn’t working sufficiently, which will cause problems within your home because moisture, lint, and gases aren’t being removed.

It also reduces the effectiveness of the dryer and clothes can burn or remain damp after a cycle.

Secondly, a vent screen will increase the risk of fire. Lint comes from the short, soft fibers that are lifted from your clothes as you wash and dry them and are highly flammable. Having lint building up in or around the vent can be dangerous as the heat exhausted from the dryer can ignite the fibers.

Size of the Terminal Opening

The size of the terminal is stated in Section M1502.3.1 of the IRC. The ducting for the exhaust must give a minimum of 12.5 in2 (8065 mm2) for the open area. The passageway terminal must also be the same size as the whole line.

The size of the terminal cannot change without compromising the air pressure system that moves the byproducts through the ductwork. Therefore, the IRC provided the smallest size that can provide the minimum exhaust rate.

Flexible dryer ducting and a vent full of lint with a text saying the minimum open area of a ducting exhaust

If your ductwork or terminal point is incorrectly sized, there would not be sufficient air exhaustion and ventilation.

If the terminal is smaller, it increases the static pressure (friction), which slows the air. The consequences of slowing airflow in a dryer duct can increase condensation and cause dripping and even duct damage.

Check Local Codes As Well

It is always essential to check your local codes. Except for Wisconsin, the American states follow the guidelines set by the IRC.

However, the individual regions can make amendments or modifications to the building code to make it more relevant to the conditions and situations for that state.

So, before you start adding or adjusting, you need to confirm that your state doesn’t have special requirements for the vent termination point.


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