A dryer vent moves hot, moist air and lint outside your home
A dryer vent is a duct that carries warm, humid air from inside your dryer to the outside of your house. Without it, that moisture and lint stay trapped indoors, damaging walls, insulation, and air quality. The vent also prevents lint buildup inside the dryer itself, which is a fire hazard.
The basic path is straightforward: air leaves the dryer through a duct, travels through your wall or ceiling, and exits through an opening on the exterior of your home. That opening is covered by a damper or hood that closes when the dryer is off, preventing cold air and pests from coming back in.
Most dryers come with a short flexible duct already attached to the back. Your job is to connect that to a longer duct that runs to the outside, and to keep the whole system clear of lint.
Key Takeaways
- The vent duct should run as straight as possible to the outside wall, with no more than two 90-degree bends, because every bend slows airflow and traps lint.
- Use rigid metal duct or heavy-duty flexible duct rated for dryer use—never vinyl or thin plastic, which can sag, trap lint, and melt from heat.
- The outdoor vent hood should have a damper that opens when the dryer runs and closes when it stops, and it must not be blocked by lint or debris.
- Clean the lint trap before every load and inspect the duct at least once a year, because lint buildup reduces drying speed and increases fire risk.
- If your dryer is in a basement or interior room far from an outside wall, a vent that is too long or has too many bends will not work well and may need professional rerouting.
Choosing the right duct material
The duct connecting your dryer to the outside must be rigid metal or heavy-duty flexible metal duct rated for dryer exhaust. Rigid metal (usually aluminum) is best because it does not sag, resists crushing, and does not trap lint as easily. Flexible metal duct works too, but it must be the thick, accordion-style kind designed for dryers—not the thin vinyl or plastic ducting sold for other purposes.
Never use vinyl, plastic, or thin flexible duct. These materials can sag under their own weight, creating pockets where lint collects. They also melt or warp from the heat of dryer exhaust, which can block airflow and create a fire risk. Some building codes forbid them outright.
Duct diameter matters as well. Most household dryers use 4-inch duct, which is the standard. Check your dryer's manual or the connection on the back of the unit to confirm. Do not step down to a smaller diameter, because that reduces airflow and makes lint accumulate faster.
Running the duct to the outside
The duct should take the most direct route from the dryer to an exterior wall or roof. Every bend slows airflow and gives lint a place to settle. Most building codes allow up to two 90-degree bends; anything more and you risk the vent becoming clogged.
If your dryer is on an interior wall or in a basement, the duct may have to travel a long distance or make several turns to reach the outside. A duct longer than 25 feet, or one with more than two bends, will not move air efficiently. In that case, you may need to reroute the dryer itself or install a booster fan—a professional HVAC technician can assess whether either option is practical for your home.
find the duct with metal hose clamps or duct tape rated for high heat. Do not use regular duct tape, which fails in heat. Clamp the duct at the dryer outlet, at any joints, and at the wall or roof penetration. Sagging duct traps lint, so support it every few feet if it runs horizontally.
Installing the outdoor vent hood
The duct exits through a vent hood or termination cap mounted on the outside of your home. This hood has a damper—a flap that opens when hot air pushes it and closes when the dryer stops, blocking outdoor air and pests from entering.
The hood should be mounted as close to the exterior wall as possible, with the duct running straight into it. Avoid long runs of duct outside the wall, because they cool the air and cause condensation and lint to accumulate. The hood opening should be at least 12 inches away from windows, doors, or other air intakes, and it should not be blocked by siding, trim, or landscaping.
Use a hood with a damper that moves freely. Some cheaper hoods have dampers that stick or fail to close, allowing air to leak back into your home. Test the damper by hand before installation to make sure it swings easily. Once installed, check it periodically to confirm it still opens and closes without resistance.
Maintaining your vent system
Lint is the enemy of a working dryer vent. It reduces airflow, makes the dryer work harder and run longer, and creates a fire hazard. Clean the lint trap inside the dryer before or after every load—this is the single most important maintenance step. A full lint trap blocks air and heat, making clothes take twice as long to dry.
Once a year, inspect the duct itself. Disconnect the duct from the back of the dryer and look inside with a flashlight. If you see lint buildup, use a dryer vent brush—a long, flexible brush designed for this purpose—to scrub the inside of the duct. These brushes are inexpensive and available at hardware stores. Feed the brush through the duct from the dryer end, then from the outdoor hood end, to dislodge lint trapped in the middle.
Check the outdoor hood as well. Make sure the damper moves freely and is not clogged with lint or debris. If the hood is caked with lint, clean it out by hand or with a brush. A blocked hood forces the dryer to work against back pressure, which shortens its life and wastes energy.
If your dryer is taking much longer than usual to dry clothes, or if the hood damper is not opening when the dryer runs, the vent is likely clogged. Clean it before calling a technician, because a blocked vent is the most common reason for poor dryer performance.
When to call a professional
You can handle basic vent cleaning and inspection yourself, but some situations call for a professional HVAC technician or dryer specialist. If your dryer is far from an exterior wall and the vent requires more than two bends or is longer than 25 feet, a professional can assess whether rerouting is possible or whether a booster fan would help. If you smell burning lint or see smoke coming from the hood, stop using the dryer and have the vent inspected before running it again.
If you are installing a new dryer or rerouting an existing vent, a technician can may support the duct is sized correctly, supported properly, and sealed at all joints. They can also confirm that your installation meets local building codes, which vary by region.
Frequently Asked Questions
Can I vent my dryer into the attic or crawlspace instead of outside?
No. Venting indoors introduces moisture and lint into your home, which damages insulation, promotes mold growth, and wastes the dryer's heat. All dryers must vent to the exterior. Some older homes were vented this way, but it is not safe or code-compliant.
How often should I clean the dryer vent duct?
Clean the lint trap before every load. Inspect and brush the duct itself at least once a year, or more often if you notice the dryer taking longer to dry clothes. Households with multiple people or frequent laundry may need to clean the duct twice a year.
What is the difference between flexible and rigid dryer duct?
Rigid metal duct is straight, does not sag, and resists lint buildup better. Flexible metal duct can bend around obstacles but may sag if not supported and can trap lint in its ridges. Both work if installed correctly; rigid is preferred when the route allows it.
Why is my dryer vent damper stuck closed?
Lint and debris accumulate on the damper flap, preventing it from opening. Clean the hood and damper by hand, removing any visible lint. If the damper still does not move freely, it may need to be replaced—this is an inexpensive part available at hardware stores or online.
Do I need a permit to install or replace a dryer vent?
This depends on your local building code. Some jurisdictions require a permit for any ductwork installation; others do not. Contact your local building department or code office before starting work to confirm what is required in your area.