The Basic Setup: Where the Vent Goes and Why
A dryer vent carries hot, moist air from inside your dryer to the outside of your home. Without it, moisture builds up in the drum, clothes stay damp, and the machine works harder and hotter than it should. The vent runs from the back of the dryer through your wall or roof to an exterior opening, usually 4 inches in diameter.
The vent path matters because longer runs, sharp bends, and crushed ducts all slow airflow and trap lint. A straight, short vent works best. If your dryer is far from an outside wall, you may need to run the duct through walls or the attic, which requires planning before installation.
Key Takeaways
- Dryer vents must run to the outside of your home, not into an attic or crawlspace, because moisture will damage the structure.
- The duct should be rigid metal or semi-rigid, not flexible plastic or foil, because lint sticks to smooth plastic and crushes easily.
- The vent opening on the outside wall or roof needs a damper hood that closes when the dryer is off to stop cold air and pests from entering.
- Lint buildup in the duct reduces drying speed and increases fire risk, so the duct should be cleaned once a year or more if drying slows.
Choosing the Right Duct Material
Rigid metal duct is the best choice. It does not crush, resists lint buildup, and lasts the life of the dryer. It costs more upfront but requires less maintenance and fewer replacements.
Semi-rigid metal duct (the accordion-style metal tube) works well if you need some flexibility to fit around obstacles. It is cheaper than rigid duct and still resists crushing better than plastic. The ridges can trap lint over time, so it needs more frequent cleaning than smooth rigid duct.
Avoid flexible plastic or foil ducts. Lint clings to the smooth interior, buildup happens fast, and the material crushes easily under its own weight or when furniture is pushed against it. These ducts are common in older homes and mobile homes but are a fire hazard and should be replaced.
Running the Duct from Dryer to Outside
Start at the dryer outlet — the opening on the back of the machine where the vent connects. Attach your duct to this outlet with a hose clamp or duct tape, making sure the connection is tight so air does not leak into the wall.
Route the duct to the nearest outside wall or roof. Keep the run as straight as possible. If you must bend the duct, use 45-degree elbows rather than sharp 90-degree turns, because sharp bends slow airflow and trap lint. Each bend adds resistance, so minimize them.
If the duct runs through a wall, drill a hole slightly larger than the duct diameter and feed the duct through. Seal the gap around the duct with caulk or foam sealant to stop air leaks and prevent pests from entering. If the duct runs through an attic or crawlspace, it must not stop there — it must continue all the way to the outside. Never vent into an attic, basement, or crawlspace because the moisture will rot wood, encourage mold, and damage insulation.
Installing the Exterior Vent Hood
The vent opening on the outside of your home needs a damper hood — a metal or plastic box with a hinged flap inside. When the dryer runs, hot air pushes the flap open. When the dryer stops, the flap closes, blocking cold air, rain, and pests from entering the duct.
Choose a hood that matches your duct diameter (usually 4 inches). Attach it to the outside of the wall or roof with the duct connected to the inlet. Seal around the hood with caulk or flashing to stop water from leaking in around the edges. If the hood is on the roof, use roof flashing and roofing cement to create a watertight seal.
Make sure the hood opening is not blocked by siding, trim, or landscaping. Blocked vents force hot air back into the duct, which slows drying and increases fire risk. The opening should be clear on all sides.
Cleaning and Maintaining the Vent
Lint accumulates in the duct over time, even with a lint trap inside the dryer. Check the duct at least once a year, or sooner if clothes take longer to dry. A hand-crank duct brush or a shop vacuum with a hose attachment can pull lint from the duct.
To clean the duct, disconnect it from the dryer or the exterior hood (whichever is easier to access), and feed the brush or vacuum hose through. Work from both ends if possible to push lint out completely. If the duct is crushed or heavily clogged, it may be faster to replace it than to clean it.
Check the exterior hood damper regularly. If it sticks or does not close fully, clean it or replace it. A stuck damper lets cold air and moisture back into the duct, which defeats the purpose of the vent.
Common Mistakes That Reduce Vent Performance
Flexible plastic duct is the most common mistake. It crushes easily, traps lint, and is a fire hazard. Replace it with rigid or semi-rigid metal duct.
Venting into an attic or crawlspace instead of outside is another serious error. The moisture will rot wood framing and encourage mold growth. The duct must run all the way to the exterior.
Long duct runs with multiple bends slow airflow significantly. If your dryer is far from an outside wall, consider moving the dryer closer to an exterior wall, or accept that drying will be slower and the machine will work harder. A run longer than 25 feet or with more than four 90-degree bends will noticeably reduce performance.
Blocked or clogged vents are also common. If clothes are still damp after a full cycle, the vent is likely restricted. Clean it before assuming the dryer is broken.
When to Call a Professional
If the duct runs through walls or the attic and you are not comfortable cutting holes or running ducts through framing, hire a contractor or HVAC technician. They can route the duct safely and seal it properly.
If you need to move the dryer location or install a new vent opening in the roof, a contractor can handle the structural work and flashing. Roof work in particular should be done by someone experienced with roofing to avoid leaks.
If the duct is crushed, clogged, or damaged and you cannot access it easily, a professional duct cleaning service can remove the blockage or replace the duct.
Frequently Asked Questions
Can I use flexible plastic duct for my dryer vent?
No. Flexible plastic duct is a fire hazard because lint sticks to the smooth interior and builds up quickly, restricting airflow and trapping heat. Metal duct — rigid or semi-rigid — is required by most building codes and is much safer.
What happens if I vent my dryer into the attic?
The hot, moist air will condense in the attic and soak the wood framing, insulation, and roof decking. This causes rot, mold growth, and structural damage over time. Dryer vents must run to the outside of the home, not into any enclosed space.
How often should I clean my dryer vent?
At least once a year, or sooner if clothes take longer to dry than they used to. Lint buildup slows airflow, makes the dryer work harder, and increases fire risk. If you have a long duct run or multiple bends, clean it more often.
Does the exterior hood damper need to be cleaned?
Yes. Check it a few times a year to make sure the flap moves freely and closes completely when the dryer is off. A stuck damper lets cold air and moisture back into the duct, which reduces efficiency and can cause condensation inside the duct.
What size duct do I need for my dryer?
Most household dryers use 4-inch diameter duct. Check your dryer manual or the outlet on the back of the machine to confirm. Some older or commercial dryers may use 5-inch or 6-inch duct, but 4-inch is standard for residential machines.