The dryer vent runs from the back of your machine to the outside of your home
The dryer vent is a duct that carries hot, moist air and lint from inside your dryer to the outdoors. It starts at the exhaust port on the back of the dryer, runs through your wall or floor, and exits through an opening in your exterior wall, roof, or foundation. The vent must reach outside—not into your attic, crawlspace, or basement—because the moisture and lint have nowhere else to go and will damage your home if trapped indoors.
Most dryer vents exit through the side of the house, usually near ground level on the wall where the laundry room is located. Some homes vent through the roof, and a few older installations vent into a basement or crawlspace, which is a serious problem that should be corrected. The path the vent takes depends on where your dryer sits, how your house is framed, and what's already in the walls.
Key Takeaways
- A dryer vent must exit completely outside your home, not into an attic, basement, or crawlspace, because moisture will rot wood and encourage mold.
- Most residential dryer vents use 4-inch rigid or semi-rigid metal duct and exit through the nearest exterior wall at ground level.
- The vent should be as short and straight as possible—every foot of duct and every turn reduces airflow and traps lint inside the machine.
- A damper or flapper door at the exterior opening closes when the dryer is off, preventing cold air and pests from entering your home.
- If your dryer currently vents into a basement, attic, or crawlspace, the duct should be rerouted to the outside as soon as possible.
How the vent path is built during installation
When a dryer is installed, the duct is routed from the exhaust port on the back of the machine to the exterior wall. The installer measures the distance, cuts or drills an opening through the wall (usually 4 inches in diameter), and runs the duct through the wall cavity. The duct is then connected to a vent hood—a cover with a damper—on the outside of the house.
The route depends on the layout of your home. In a single-story house with the laundry room on an exterior wall, the vent can go straight through. In a two-story home, the duct might run up through the wall cavity to exit higher on the wall, or it might run horizontally to a different wall. In some cases, the duct runs under the floor to exit on a different side of the house. The key is that it must reach outside; there is no exception to this rule.
Why the vent cannot go into your attic, basement, or crawlspace
A dryer produces about 5 gallons of water vapor per load. If that moisture is vented into an enclosed space instead of outside, it condenses on wood framing, insulation, and stored items. Over weeks and months, this causes wood rot, mold growth, and structural damage that is expensive to repair. Moisture in an attic can also damage roof sheathing and shingles from the inside.
Some older homes or rental properties have dryers vented into basements or crawlspaces. This is a code violation in most jurisdictions and creates the same moisture problems. If your dryer is currently vented this way, the duct should be rerouted to the exterior. This usually means running the duct up through the wall to exit on an exterior wall, or drilling a new opening in the foundation or rim joist.
The duct material and why it matters
Dryer ducts are made from three main materials: rigid metal (galvanized steel), semi-rigid metal (flexible aluminum), and flexible plastic or foil. Rigid metal is the best choice because it resists crushing, does not trap lint as easily, and lasts the longest. Semi-rigid metal is acceptable and easier to route around obstacles. Flexible plastic or foil ducts should be avoided—they crush easily, trap lint, and can be a fire hazard if lint builds up inside.
The duct diameter is almost always 4 inches for residential dryers. The duct should be as short as possible and as straight as possible. Every foot of duct and every 90-degree turn reduces airflow slightly, which means lint stays in the duct longer and is more likely to accumulate. If your duct is longer than 25 feet or has more than two or three turns, lint removal becomes harder and the dryer has to work longer to dry clothes.
The vent hood and damper on the outside
At the exterior end of the duct, a vent hood (also called a vent cap or termination) covers the opening. The hood has a damper—a flapper door that opens when the dryer runs and closes when it stops. The damper prevents cold outside air, rain, and pests from entering your home when the dryer is off. Most hoods are made of plastic or aluminum and are inexpensive to replace if they crack or the damper stops working.
The hood should be mounted flush against the exterior wall, with no gaps around it. If the hood is loose or the damper is stuck, warm air and moisture can leak back into the wall cavity. A stuck damper also means the dryer has to work harder to push air out, which increases drying time and energy use. If you notice your dryer is taking longer than usual to dry clothes, a stuck damper is one of the first things to check.
What happens if the vent is blocked or too long
Lint naturally accumulates inside the duct over time, even with a lint trap in the dryer. If the duct is very long, has many turns, or is made of flexible plastic, lint builds up faster. A partially blocked vent means the dryer has to work harder to push hot air out, so clothes take longer to dry and the dryer runs hotter. This wastes energy and can shorten the life of the dryer.
A severely blocked vent can cause the dryer to overheat and shut off mid-cycle, or in rare cases, create a fire hazard. Most dryer fires start in the duct, not in the machine itself. The best prevention is to clean the lint trap before every load and to have the duct professionally cleaned once a year if it is longer than 25 feet or has multiple turns. If your duct is very long or poorly routed, rerouting it to a shorter path is worth the cost.
How to find where your vent goes if you are unsure
If you have recently moved into a home or are not sure where your dryer vent exits, you can trace it yourself. Start at the back of the dryer and follow the duct as it leaves the machine. Look for where it enters the wall, and then go outside and look for the vent hood. It is usually a rectangular or round opening with a damper flap visible from the outside. If you cannot find it, check the roof, the foundation, and all exterior walls on the side of the house where the laundry room is located.
If you find that the vent goes into an attic, basement, or crawlspace instead of outside, or if you cannot find the vent at all, contact a dryer vent specialist or HVAC technician. They can trace the duct, identify where it terminates, and recommend whether it needs to be rerouted. This is not a repair you should attempt yourself unless you have experience working with ducts and exterior walls.
Frequently Asked Questions
Can a dryer vent go through the roof instead of the wall?
Yes, some homes vent through the roof, especially if the laundry room is far from an exterior wall or in the center of the house. A roof vent works fine as long as the damper is installed correctly and the duct is sealed where it passes through the roof. However, roof vents are more exposed to weather and can be harder to clean, so wall vents are generally preferred.
What if my vent hood damper is stuck or broken?
A stuck damper means air cannot flow out freely, so the dryer works harder and clothes take longer to dry. You can replace the hood itself—it is inexpensive and usually clips or screws on—or call a technician to inspect the duct and damper. Do not ignore this, because it reduces efficiency and can lead to lint buildup.
How often should the dryer vent be cleaned?
Clean the lint trap inside the dryer before every load. Have the duct professionally cleaned once a year if it is 25 feet or shorter with few turns, or twice a year if it is longer or has multiple bends. If clothes are taking noticeably longer to dry, the duct may need cleaning sooner.
Is it safe to use a flexible plastic dryer duct?
Flexible plastic ducts are not recommended. They crush easily, trap lint more readily than metal, and can be a fire hazard if lint accumulates. Use rigid metal or semi-rigid metal duct instead. If your current duct is plastic, replacing it with metal is a worthwhile upgrade.
What should I do if my dryer vent currently goes into the basement?
This is a code violation and will cause moisture damage over time. Contact a dryer vent specialist or HVAC technician to reroute the duct to an exterior wall or through the roof. This usually costs between a few hundred dollars and is far cheaper than repairing water damage and mold later.