The basic path: wet air leaves your dryer through a duct
A dryer vent moves hot, damp air out of your dryer and out of your home. When your dryer runs, it heats the drum and tumbles your clothes. That heat pulls moisture from the fabric. The dryer then pushes that hot, wet air through a metal duct — usually 4 inches in diameter — that connects to the back of the machine and runs to an outside wall or roof. The vent opening on the outside has a flap or hood that opens when air pushes through and closes when the dryer stops, keeping outdoor air and pests out.
Without a vent, that moisture would stay inside your home, making the air humid and damp. Over time, moisture builds up in walls and can cause mold. A working vent removes the problem before it starts.
Key Takeaways
- Hot, wet air from the dryer drum travels through a metal duct to the outside of your home.
- The vent flap opens when air pushes through and closes when the dryer stops, blocking outdoor air and pests.
- Lint collects in the vent duct over time and must be cleaned regularly to keep airflow strong.
- A blocked or kinked vent makes your dryer work harder, use more energy, and take longer to dry clothes.
- Most dryers vent through an exterior wall or roof, though some older models vent into the home.
Where the vent goes: exterior wall, roof, or attic
Most dryers vent to the outside of your home through the shortest path possible. The duct typically runs from the back of the dryer to an exterior wall, where it exits through a hole cut in the siding or brick. Some homes vent through the roof instead, which requires the duct to run up through the attic. A few older dryers or portable units vent into the attic or basement without going outside — this is not recommended because it releases moisture into your home.
The location matters because a longer duct or one with many bends slows airflow and traps lint. A straight, short duct works best. If your dryer is far from an exterior wall, the duct may need to run a longer distance, which is why some people use flexible aluminum or plastic ducting instead of rigid metal — it bends around corners. Flexible ducting is easier to install but collects lint more easily than rigid metal.
The vent hood and flap: keeping air moving one direction
The outside end of the vent has a hood or cap with a flap inside. When your dryer pushes air out, the pressure opens the flap and lets the warm, moist air escape. When the dryer stops, the flap closes on its own, blocking cold outdoor air, rain, and insects from entering the duct and your home.
Over time, lint can stick to the flap and prevent it from closing fully. A flap that does not close tight lets cold air leak back into your dryer, making it work harder to maintain heat. Lint buildup also blocks the opening, so the hood should be cleaned along with the duct. Some hoods have a screen to catch large lint pieces, but the screen itself can clog.
Lint buildup: why it happens and what it blocks
Every time your dryer runs, tiny fibers from your clothes break off and mix with the hot air. Most lint gets caught by the lint trap inside your dryer — the screen you pull out and empty after each load. But some lint escapes the trap and travels through the duct. Over weeks and months, lint sticks to the inside walls of the duct, especially where the duct bends or where airflow slows.
A duct clogged with lint restricts airflow. Your dryer has to work much harder to push air through, which uses more energy and generates more heat. Clothes take longer to dry. The dryer may shut off before clothes are fully dry because it overheats. In extreme cases, lint buildup can become a fire hazard because the heat has nowhere to go. Most dryer fires start in the vent duct, not inside the machine itself.
Cleaning the duct once or twice a year prevents most lint problems. You can use a vent brush kit (a long flexible brush that screws together in sections) to push lint out from inside the duct, or hire a professional vent cleaning service.
How airflow works: pressure and resistance
Your dryer has a blower fan that creates air pressure inside the drum. That pressure pushes hot air through the lint trap, then through the duct, and out the hood. The stronger the fan and the less resistance in the duct, the faster air moves out of your home.
Resistance comes from lint buildup, kinks in flexible ducting, bends in the duct path, and a clogged hood. Each obstacle slows airflow. If airflow is too slow, moisture stays in the dryer longer, and clothes stay damp. The dryer senses the moisture and runs longer to compensate, wasting energy. Some newer dryers have moisture sensors that shut off the machine when clothes are dry enough, but they still work harder if the vent is blocked.
A duct that is kinked or pinched — often where it connects to the wall or where it bends around a corner — can cut airflow in half. Checking that the duct is straight and not compressed is one of the easiest ways to improve dryer performance.
Duct materials: rigid metal, flexible aluminum, and plastic
Rigid metal ducts (usually galvanized steel) are the best choice. They do not kink, they do not collect lint as easily as flexible ducts, and they last for years. They are harder to install if your dryer is not close to an exterior wall, because they do not bend.
Flexible aluminum ducts are easier to route around obstacles and corners. They cost less than rigid metal and are faster to install. The downside is that the ridged interior surface traps lint more easily than smooth metal. Flexible ducts can also kink or pinch if furniture is pushed against them or if they are not supported properly.
Plastic or vinyl ducts should be avoided. They are cheaper but they melt if the dryer overheats, and they collect lint heavily. Some building codes do not allow plastic ducting for dryers because of fire risk.
Signs your vent is blocked or failing
A blocked vent shows up in several ways. Clothes take much longer to dry than they used to, even on the highest heat setting. The dryer gets very hot to the touch on the outside. You smell a burning odor or notice lint around the hood opening on the outside of your home. The vent flap does not open when the dryer runs, or it stays open even after the dryer stops.
If you notice any of these signs, stop using the dryer and check the vent. Pull the lint trap and look inside — if you see lint packed around the opening, the duct is likely clogged. Go outside and look at the hood. If lint is piled up around the opening or the flap is stuck, clean it out. If the problem persists after cleaning, the duct itself may be clogged and need a professional cleaning.
Frequently Asked Questions
Can I vent my dryer into my attic or basement instead of outside?
No. Venting indoors releases moisture into your home, which promotes mold growth and damages insulation and framing. Building codes require dryers to vent to the outside. Portable dryers sometimes come with indoor vent kits, but they are not a long-term solution.
How often should I clean my dryer vent?
Clean the lint trap after every load. Inspect and clean the duct at least once a year, or more often if you dry clothes frequently or have pets that shed heavily. If clothes take noticeably longer to dry, clean the vent sooner.
What is the difference between a dryer vent and a dryer exhaust?
These terms mean the same thing. The vent (or exhaust) is the duct and hood that move air out of your home. Some people use "exhaust" to refer to the air itself and "vent" to refer to the duct, but they describe the same system.
Why does my dryer vent flap stay open?
Lint buildup on the flap prevents it from closing. The flap may also be damaged or bent. Clean the hood and flap first. If the flap still does not close, it may need to be replaced. A flap that stays open lets cold air back into the dryer and reduces efficiency.
Can I use a shorter duct to improve airflow?
Yes. The shorter and straighter the duct, the better the airflow. If your dryer is far from an exterior wall, moving the dryer closer or rerouting the duct to a nearer wall will improve performance. If that is not possible, use rigid metal ducting instead of flexible to reduce resistance.