The dryer vent exits through your exterior wall, roof, or foundation
Your dryer vent carries hot, moist air and lint out of your home. That air has to go somewhere, and building code requires it to terminate outside — not into your attic, crawlspace, or back into your living space. The exact path depends on your home's layout and where your dryer sits relative to the nearest exterior wall.
Most residential dryers vent through the side of the house, usually the wall closest to the laundry room. Some vent through the roof, particularly in homes where the dryer is far from an exterior wall or in the center of the house. A small number vent through the foundation or basement rim joist. The duct itself is typically 4 inches in diameter and runs in a relatively straight line to minimize resistance and lint buildup.
Key Takeaways
- Dryer vents must terminate outside your home; venting into attics, crawlspaces, or interior walls violates building code and creates fire and mold hazards.
- The most common route is through the nearest exterior wall, which requires the shortest duct run and the least installation work.
- Roof vents are used when the dryer is far from side walls, but they are more prone to ice damming in cold climates and require regular inspection.
- The duct should slope slightly downward toward the outside to prevent moisture from pooling inside the line.
- A damper or flapper at the exterior opening closes when the dryer is off, preventing outside air, pests, and rain from entering the duct.
Side wall vents are the most common and easiest to maintain
A side wall vent exits through the exterior wall of your home, usually 12 to 24 inches above ground level. This is the standard installation because the duct run is short, the slope is straightforward to manage, and the vent opening is accessible for cleaning and inspection. Most homes have the dryer in a laundry room, basement, or garage near an exterior wall, making this the practical choice.
The duct runs from the back of the dryer, through the wall cavity, and out through a hole cut in the siding, brick, or stucco. A trim ring or flange sits flush against the exterior to seal the gap between the duct and the wall opening. A damper (also called a flapper or hood) covers the opening on the outside and swings open when the dryer runs, then closes when it stops to keep rain, insects, and cold air out.
Side wall vents do require you to keep the exterior opening clear. Lint, debris, or snow can block the damper and force moist air back into the duct, where it condenses and creates a clog. Checking the vent from outside every few months, especially in winter or after storms, takes only a minute and prevents most problems.
Roof vents work when the dryer is far from exterior walls
A roof vent is used when the dryer is in the center of the house, in an interior laundry room, or when a side wall vent would require a very long duct run. The duct travels vertically through the interior of the home and exits through the roof, usually near the peak or ridge. A roof boot (a flashing collar) seals the hole where the duct passes through the roof shingles.
Roof vents are more difficult to inspect and maintain because you have to get on the roof to see them. They are also more vulnerable to ice damming in cold climates — warm, moist air exiting the duct can melt snow on the roof, and that water can refreeze at the eaves and back up under the shingles. In regions with heavy snow or frequent freeze-thaw cycles, a roof vent may require a heat tape or insulation to prevent this problem.
If your dryer vents through the roof, inspect the vent opening and flashing at least twice a year, in spring and fall. Look for gaps in the flashing, missing or damaged shingles, or lint accumulation around the opening. If you see ice buildup around the vent in winter, that is a sign that warm air is escaping and condensing — a problem that usually means the duct is clogged and needs cleaning.
Foundation and rim joist vents are rare and require careful installation
Some older homes or homes with basements vent the dryer through the foundation wall or rim joist (the band of framing that sits on top of the foundation). This is less common than side wall or roof vents because it is harder to keep the opening sealed and because moist air venting at or below ground level can contribute to foundation moisture problems.
If your dryer vents through the foundation, the duct should slope downward toward the outside to prevent water from pooling inside the line. The exterior opening must have a damper and should be positioned so that rain and standing water do not drain back toward the foundation. A screen or cage around the opening can keep rodents and insects out, but it must not restrict airflow or trap lint.
Foundation vents are more prone to clogs because lint can settle in a horizontal or upward-sloping section of duct. If your dryer vents this way and you notice longer drying times or moisture in the basement, the duct likely needs cleaning. A professional dryer vent cleaning service can access and clear a foundation vent more easily than you can on your own.
The duct path affects how often you need to clean it
The route your vent takes determines how much lint accumulates and how quickly the duct clogs. A short, straight side wall vent with minimal bends may only need cleaning once a year. A long duct run with multiple elbows or a roof vent that slopes upward can trap lint more easily and may need cleaning every six months or more often.
The type of duct also matters. Rigid metal duct (galvanized steel or aluminum) is smoother inside and resists lint buildup better than flexible foil or plastic duct. Flexible duct is easier to install around obstacles, but it has ridges inside where lint collects. If your vent uses flexible duct, plan on cleaning it more often or consider replacing it with rigid duct if the run is short enough.
A clogged vent forces your dryer to work harder, which uses more energy and wears out the heating element faster. It also traps moisture inside the duct, where it can condense and promote mold growth. Keeping the vent clear is one of the simplest ways to extend your dryer's life and reduce your utility bills.
Dampers and caps protect the vent opening from weather and pests
The exterior end of your dryer vent should have a damper (flapper) that opens when the dryer runs and closes when it stops. This one-way valve prevents rain from entering the duct, stops cold air from flowing back into your home, and keeps birds, insects, and rodents out. A damper is required by building code in most jurisdictions.
Dampers come in several styles. A straightforward gravity damper has a flap that hangs down and swings open as air pushes it. A spring-loaded damper uses a spring to hold the flap closed and requires more air pressure to open. A magnetic damper uses a magnet to hold the flap shut. All three work, but spring-loaded and magnetic dampers tend to stay closed more reliably in windy conditions.
Over time, lint can accumulate on the damper and prevent it from closing fully. If you notice that the damper does not swing freely or stays partially open, clean it by hand or with a soft brush. A damper that does not close properly allows outside air to enter the duct, which can reduce your dryer's efficiency and allow moisture to condense inside the line.
What to do if your vent is blocked or damaged
If your dryer is taking longer than usual to dry a load, the vent is likely clogged. Start by checking the exterior opening — look for lint, debris, or a damper that is stuck closed. If the opening is clear, the clog is inside the duct and you will need to clean it from the inside.
You can clean a short, straight duct yourself using a dryer vent brush kit (available at hardware stores for $20 to $50). Disconnect the duct from the back of the dryer, insert the brush, and push it toward the exterior opening while rotating it to loosen lint. For longer runs, multiple bends, or roof vents, a professional dryer vent cleaning service is faster and more thorough — they use powered equipment that can reach the entire length of the duct.
If the duct is damaged (crushed, kinked, or torn), it should be replaced. Damage restricts airflow and can allow lint to escape into the wall cavity or attic, creating a fire hazard. Rigid metal duct is more durable than flexible duct and is worth the extra cost if you are replacing a damaged line.
Frequently Asked Questions
Can I vent my dryer into the attic or crawlspace?
No. Building code prohibits venting a dryer into any interior space. Moist air in the attic or crawlspace promotes mold growth, rots wood framing, and can damage insulation. Venting into the attic also creates a fire hazard because lint can accumulate on rafters and other surfaces. The vent must terminate outside.
What if my dryer vent is too long?
A duct longer than 25 feet (or shorter if there are multiple bends) creates excessive resistance and makes the dryer work harder. If your vent run is too long, consider relocating the dryer closer to an exterior wall, adding a booster fan to the duct, or switching to a condenser or heat pump dryer that does not require external venting. A professional can measure your duct and recommend the best option.
Why is water pooling inside my dryer vent?
The duct should slope downward toward the outside so that condensation drains out rather than pooling inside. If water is collecting, the duct may be installed level or sloping the wrong direction, or it may be clogged and trapping moisture. Have the duct inspected and cleaned, and ask a professional to check the slope and reposition it if needed.
Do I need to insulate my dryer vent?
Insulation is not required by code, but it can help in cold climates. Insulating a roof vent or a duct that runs through an unheated space reduces condensation and helps prevent ice damming. Wrap the duct with foam pipe insulation (available at hardware stores) or ask a professional to install it during a cleaning or repair.
Can I use a flexible dryer vent hose instead of rigid duct?
Flexible hose is easier to install around obstacles, but it traps lint more easily than rigid duct and is more prone to kinking and crushing. If you use flexible hose, keep the run as short as possible, inspect it regularly for damage, and clean it more often. Rigid metal duct is the better choice for longer runs or permanent installations.