The basic route: drill through the wall, attach the duct, and seal it
A dryer vent that runs outside requires four main steps: cut or drill a hole through your exterior wall, insert a vent hood (the part that sticks out), connect your dryer's duct to it from the inside, and seal the gap so air and pests do not leak in around the edges. Most people can do this in an afternoon with a drill, a hole saw, caulk, and basic hand tools. The hardest part is usually deciding where to put the hole — you want it as short and straight as possible, ideally on the same wall as your dryer.
The vent hood itself is a metal or plastic fitting that mounts flush against your exterior wall. It has a damper (a flap inside) that opens when the dryer runs and closes when it stops, keeping cold air and pests out. You buy the hood at any hardware store for $15 to $40 depending on material and finish. The duct that connects your dryer to the hood is typically 4 inches in diameter and comes in flexible aluminum or rigid metal — flexible is easier to route around obstacles, but rigid moves air more efficiently.
Key Takeaways
- Locate your hole on the same wall as the dryer, as close as possible, to keep the duct run short and straight.
- Use a 4-inch hole saw to cut through drywall and exterior sheathing, then insert the vent hood and find it with the mounting brackets that come with it.
- Connect flexible or rigid 4-inch duct from your dryer's outlet to the vent hood, using duct clamps at each connection point.
- Seal the gap between the vent hood and the wall with caulk or foam sealant to prevent air leaks and pest entry.
- A vent that runs more than 25 feet or has more than four 90-degree bends will reduce airflow and may require a booster fan.
Choosing the location and marking the hole
Walk around your house and identify which exterior wall is closest to your dryer. Ideally, the duct will run straight out or with only one or two bends. Avoid routing the vent under a soffit, into a crawlspace, or near a window or door — lint and moisture can damage siding or blow back inside. Check the outside wall for obstacles: electrical outlets, water lines, or structural framing. If you are unsure what is inside the wall, drill a small pilot hole first and look through it.
Mark the center point of your hole on the interior wall at the height of your dryer's vent outlet. Most dryers have the outlet on the back or bottom-rear, so measure from the floor or from the dryer itself. Go to the exterior wall at the same spot and mark the center point there too. This is where your hole saw will go. Make sure the spot is clear of trim, siding seams, or anything that will make the hole saw bind.
Cutting the hole and installing the vent hood
Use a 4-inch hole saw attached to a drill. Start from the inside and drill slowly — the hole saw will break through the drywall first, then the rim board or sheathing, then the exterior siding or sheathing. Have someone outside watch for the hole saw tip to poke through, or drill from the outside if you can reach it safely. Once the hole is complete, remove any loose debris or insulation from inside the wall cavity.
The vent hood comes with a flange (a flat rim) that sits against the exterior wall. Slide the hood through the hole from outside so the flange sits flush. Most hoods have mounting tabs or a bracket on the back — use the screws or fasteners provided to find it to the wall sheathing. If your siding is vinyl or wood, you may need to drill pilot holes first to prevent splitting. Caulk around the flange with exterior-grade caulk to seal the gap between the hood and the wall.
Connecting the duct from your dryer to the vent hood
Locate your dryer's vent outlet on the back or bottom. Disconnect any existing duct or vent hose. Measure the distance from the outlet to the vent hood on the wall — this is the length of duct you need. Buy 4-inch flexible aluminum duct or rigid metal duct to match that length, plus a few extra feet if you need to route around obstacles.
Slide one end of the duct onto the dryer's outlet and find it with a duct clamp (a metal band that tightens with a screw). Route the duct to the vent hood, keeping bends gentle and the run as straight as possible. Avoid kinks or sharp angles, which trap lint and reduce airflow. Slide the other end of the duct onto the vent hood's inlet and find it with another clamp. Tighten both clamps firmly so the duct does not slip off during operation.
Sealing gaps and checking for leaks
Caulk any gap between the vent hood flange and the wall with exterior-grade silicone or acrylic caulk. This prevents air leaks, water infiltration, and pest entry. If the gap is larger than a quarter-inch, use foam backer rod first, then caulk over it. Let the caulk cure for the time recommended on the tube — usually 24 hours — before running the dryer.
Run the dryer for a few minutes and go outside to check that air is flowing out of the vent hood. You should feel warm, moist air and see the damper flap open. If you do not feel airflow, the duct may be kinked, clogged, or disconnected inside the wall. If the damper does not open, it may be stuck with lint or installed backward. Most dampers are directional and only open one way.
When your duct run is too long or has too many bends
Building codes and dryer manufacturers limit duct runs to 25 feet in a straight line, or less if there are bends. Each 90-degree bend counts as 5 feet of equivalent length — so a 15-foot run with two bends is treated as a 25-foot run. If your duct run exceeds these limits, airflow drops and lint accumulates inside the duct, creating a fire hazard and reducing drying speed.
If you cannot shorten the run, install a booster fan (also called a duct booster or inline fan) inside the duct. This is a small motorized fan that mounts inside the duct and pushes air toward the vent hood. Booster fans cost $40 to $100 and plug into a standard outlet. They are not required by code but are a practical solution when the duct run is unavoidable. Some dryers have built-in booster fans, so check your manual before buying one.
Maintenance to keep the vent working
Clean the lint trap after every load — this is the single most important step. A clogged lint trap forces the dryer to work harder and heats up the duct, which can damage the damper or start a fire. Once or twice a year, disconnect the duct from the dryer and use a duct brush or shop vacuum to remove lint buildup inside. Check the exterior vent hood to make sure the damper moves freely and is not blocked by lint, leaves, or bird nests.
If the dryer takes longer than usual to dry clothes, or if the vent hood damper does not open, the duct is probably clogged. Disconnect the duct and brush it out. If the damper is stuck, spray it with a silicone lubricant and work it open gently — do not force it or you may break the hinge. Replace the damper if it is cracked or will not stay open.
Frequently Asked Questions
Can I vent the dryer into the attic or basement instead of outside?
No. Dryer exhaust contains moisture and lint that will damage insulation, promote mold, and create a fire hazard. Venting to the attic or basement is a code violation in most jurisdictions and will void your dryer warranty. The vent must go to the outside.
What if I cannot drill through the wall because of framing or utilities?
Move the hole location a few feet up, down, or to the side. If the entire wall is blocked, vent through an adjacent wall or a different side of the house. The longer the duct run, the less efficient the system, but a longer run is still better than venting indoors. Consult a contractor if you are unsure whether a location is safe.
Do I need a damper in the vent hood?
Yes. A damper prevents cold outside air from flowing backward into the dryer when it is off, which wastes energy and can cause condensation inside the drum. All vent hoods sold at hardware stores include a damper. If yours does not, replace the hood.
How often should I clean the duct?
Clean the lint trap after every load. Inspect and brush the duct once or twice a year, or more often if you notice the dryer is taking longer to dry clothes. If you have a long duct run (over 20 feet) or a booster fan, check it more frequently because lint builds up faster in those systems.
What size hole saw do I need?
A 4-inch hole saw matches the standard dryer vent outlet and duct size. Some older dryers use 3-inch vents, so check your dryer's manual or the outlet itself before buying the hole saw. Hardware stores sell hole saws individually or in kits.