The Basic Setup: Where the Vent Goes and Why
A clothes dryer vent carries hot, moist air from inside your dryer to the outside of your home. The vent starts at the back of the dryer, runs through your wall or ceiling, and exits through an opening on your exterior wall or roof. Without proper venting, moisture builds up inside the drum, clothes stay damp, and your dryer works twice as hard to dry a single load.
The vent also removes lint—the fibrous debris that comes off your clothes. Lint that stays inside the vent duct clogs the airflow, raises the temperature inside the dryer, and creates a serious fire hazard. Building codes in most places require that dryer vents exit directly outside, not into your attic, crawlspace, or basement.
The most common setup uses a flexible metal duct (called flex duct or dryer duct) that connects the dryer outlet to a wall or roof vent. Some older homes use rigid metal duct, which is actually better for airflow but harder to install if you need to move the dryer.
Key Takeaways
- The vent duct must run from the back of your dryer to an opening on the outside of your home, not into an attic or basement.
- Use smooth metal duct or rigid metal pipe rather than plastic or foil, because plastic melts and foil crushes easily, both blocking airflow.
- Keep the duct as short and straight as possible—every 45-degree bend adds resistance and reduces drying speed.
- Clean the lint trap after every load and inspect the duct opening outside at least twice a year for lint buildup or bird nests.
- If your dryer takes longer than 45 minutes to dry a normal load, the vent is likely clogged and needs cleaning.
Choosing the Right Duct Material
The duct that carries air from your dryer to the outside must be metal. Flexible metal duct (also called flex duct or accordion duct) is the easiest to install, especially if your dryer is not directly against an exterior wall. Rigid metal duct is harder to work with but moves air more efficiently because it has fewer places for lint to catch.
Never use plastic duct or foil-backed insulation duct. Plastic melts when exposed to the heat of the dryer exhaust, and foil crushes under its own weight or when you accidentally step on it. Both trap lint and restrict airflow. Flexible metal duct should be 4 inches in diameter to match your dryer outlet—check the back of your dryer to confirm the size before you buy.
When you buy flex duct, look for the smooth interior type, not the ridged kind. Ridges trap lint more easily. Smooth flex duct costs a few dollars more but lasts longer and works better. Plan to replace the duct every 3 to 5 years, or sooner if you notice it is crushed or kinked.
Running the Duct from Dryer to Outside
Start at the outlet on the back of your dryer. Slide one end of the flex duct onto the outlet and find it with a hose clamp or metal duct tape (the kind with the mesh backing, not regular tape). Tighten the clamp so the duct does not slip off, but do not crush the duct itself.
Run the duct toward your exterior wall or roof opening. Keep it as straight as possible. Every 45-degree bend adds resistance and slows the airflow, making your dryer work harder and take longer to dry clothes. If you must bend the duct, use a 45-degree elbow fitting rather than crimping the duct by hand—a crimped duct stays partially collapsed and never fully opens again.
Avoid running the duct through your attic, crawlspace, or basement. These spaces are not designed to handle the heat and moisture from dryer exhaust. Moisture in an attic can rot wood and encourage mold. If your dryer is far from an exterior wall, consider moving the dryer closer to an outside wall rather than running a very long duct.
Where the duct passes through a wall, use a wall vent kit that includes a collar and damper flap. The damper flap opens when the dryer runs and closes when it stops, preventing outside air and pests from entering your home. Seal any gaps around the collar with caulk or weatherstripping.
Installing the Exterior Vent Opening
The vent opening on the outside of your home should be a louvered vent hood or a duct hood with a damper flap. This flap opens when warm air pushes out and closes when the dryer stops, keeping rain, snow, and pests out. Do not use a straightforward open pipe—it will let birds and insects nest inside your duct.
The vent hood should be mounted on a wall or roof where it will not be blocked by landscaping, snow, or debris. Check it every few months, especially in winter or after storms. If lint is visible around the opening or if the flap does not move freely, the duct is clogged and needs cleaning.
If you have a roof vent, make sure it is flashed properly where it meets the roof so water does not leak inside. A poorly flashed roof vent is one of the most common sources of water damage in homes. If you are not comfortable working on a roof, hire a professional to install or repair the flashing.
Cleaning and Maintaining Your Vent
The lint trap inside your dryer should be cleaned after every load. A full lint trap blocks airflow and makes your dryer less efficient. Pull out the trap, wipe it with your hand or a brush, and replace it. This takes 30 seconds and is the single most important maintenance step you can do.
Once or twice a year, inspect the vent opening on the outside of your home. Look for lint buildup around the flap, bird nests, or debris blocking the opening. If you see lint, use a brush or your hand to clear it away. If the flap is stuck or damaged, replace the vent hood.
If your dryer is taking longer than 45 minutes to dry a normal load of towels or jeans, the duct is likely clogged inside. You can try disconnecting the duct from the back of the dryer and using a leaf blower to blow air backward through it, pushing lint out the exterior opening. Wear a dust mask—lint will blow everywhere. For a thorough cleaning, you can buy a dryer vent cleaning kit with a brush that attaches to a power drill, or hire a professional vent cleaning service.
Common Mistakes That Block Airflow
The most common mistake is using the wrong duct material. Plastic duct melts, foil duct crushes, and both trap lint. Stick with smooth metal flex duct or rigid metal pipe.
The second mistake is running the duct too long or with too many bends. A duct longer than 35 feet or with more than four 45-degree bends will restrict airflow significantly. If your dryer is far from an exterior wall, moving the dryer is often easier than running a long duct.
The third mistake is venting into an attic or basement instead of outside. This traps moisture where it can rot wood and grow mold. It also makes your heating and cooling system work harder because you are exhausting conditioned air.
The fourth mistake is ignoring the lint trap or the exterior vent opening. A clogged lint trap reduces efficiency when ready. A clogged exterior opening reduces efficiency more slowly but eventually makes the dryer nearly useless and creates a fire hazard.
When to Call a Professional
If your dryer is taking much longer than normal to dry clothes and cleaning the lint trap does not help, the duct is clogged inside. You can try the leaf blower method, but if that does not work, a professional vent cleaning service has better tools and can reach clogs deep inside the duct or in the elbows.
If you need to install a new vent opening in your roof or exterior wall, or if you need to repair flashing around a roof vent, hire a professional. Mistakes with roof work can lead to water leaks that are expensive to fix later.
If you are not comfortable working with flex duct or metal fittings, or if your dryer is in a tight space, a professional can install the vent quickly and correctly. The cost is usually between $150 and $300 for a straightforward installation.
Frequently Asked Questions
Can I vent my dryer into the basement or attic to keep warm air inside?
No. Venting into an attic or basement traps moisture that rots wood, encourages mold, and can damage insulation. Building codes require venting to the outside. The small amount of heat you save is not worth the damage risk.
What size duct do I need?
Most household dryers use a 4-inch duct. Check the outlet on the back of your dryer to confirm. Some older or commercial dryers use 5-inch or 6-inch ducts. Buy the size that matches your dryer outlet.
How often should I replace the duct?
Replace flex duct every 3 to 5 years, or sooner if it is crushed, kinked, or visibly deteriorating. Rigid metal duct lasts much longer but is harder to install. Inspect the duct at least twice a year for damage.
What if my dryer is in the middle of my home, far from any exterior wall?
A duct longer than 35 feet or with more than four bends will restrict airflow and make your dryer inefficient. If possible, move the dryer closer to an exterior wall. If you cannot move it, a professional vent installer can assess whether a long duct run is practical for your layout.
Is it safe to use duct tape to seal the duct connections?
No. Regular duct tape fails in the heat of dryer exhaust and leaves sticky residue. Use metal hose clamps or metal duct tape (the kind with mesh backing) to find flex duct to the dryer outlet and vent hood. For sealing seams in rigid duct, use metal duct tape or mastic sealant rated for high heat.