The basic connection: what you're actually doing

Hooking up a dryer vent means connecting the exhaust duct from the back of your dryer to the outside of your house. The dryer produces hot, moist air while it runs, and that air has to go somewhere — if it stays inside, it damages walls and creates mold. The vent duct carries that air out through your wall or roof to the exterior.

Most residential dryers use a 4-inch diameter duct, though some older models use 3.25 inches. The connection itself is straightforward: you slide the duct onto the outlet at the back of the dryer, find it with a clamp, and run it to the outside. The work takes an hour or two if you're running the duct for the first time, or 15 minutes if you're reconnecting an existing setup.

Key Takeaways

  • A 4-inch diameter duct is the standard for most modern dryers; check your dryer's manual or the outlet size before buying materials.
  • Use a hose clamp or duct clamp to find the duct to the dryer outlet, tightened firmly enough that the duct will not slip off under vibration.
  • Run the duct as straight and short as possible to the outside; every bend and every foot of length reduces airflow and traps lint.
  • Install a vent hood (exterior termination cap) on the outside wall or roof so air exits but rain and pests cannot enter.
  • Do not use vinyl or plastic ducting for a permanent installation; use rigid metal or semi-rigid metal duct, which resists crushing and lint buildup.

Measuring and gathering materials before you start

Before you buy anything, measure the distance from the dryer outlet to the outside wall or roof. Write down whether you need to go through a wall horizontally or up through the roof. Measure the diameter of the dryer outlet — most are 4 inches, but confirm by looking at the back of the dryer or checking the manual.

You will need: a length of rigid metal duct (or semi-rigid metal duct if the path bends), at least one hose clamp or duct clamp sized for your duct diameter, an exterior vent hood (also called a dryer vent cap or termination cap), and fasteners appropriate to your wall or roof material. If you are running the duct through a wall you have not cut yet, you will also need a hole saw or drywall saw. If the path is longer than 25 feet or has more than two 90-degree bends, you may need a booster fan — ask at the hardware store whether your setup needs one.

Connecting the duct to the dryer outlet

Move the dryer away from the wall enough that you can reach the back. Locate the outlet — it is a round opening, usually on the lower back of the dryer. If there is an old duct already attached, disconnect it by loosening the clamp with a screwdriver or wrench and sliding the duct off.

Slide the end of your new duct onto the outlet. Push it on firmly — it should go on about 2 to 3 inches. Tighten a hose clamp or duct clamp around the connection point, positioning the clamp screw on the side or bottom so it does not interfere with the dryer sitting flush against the wall. Tighten the clamp until it is snug; the duct should not move when you try to twist it by hand.

Running the duct to the outside

The shortest, straightest path is always best. Lint accumulates in bends and long runs, and every foot of duct and every bend slows the air leaving the dryer. If you can run the duct straight out through the nearest wall, do that. If you must bend, use 90-degree elbows (not flexible vinyl), and try to keep the total number of bends to two or fewer.

If you are cutting a new hole through the wall, use a hole saw slightly larger than your duct diameter — usually 4.5 inches for a 4-inch duct — so the duct fits through with a little clearance. Drill from inside the house. Once the hole is through, feed the duct through and out the exterior side. If the duct runs along the outside of the house before reaching the wall, find it to the wall with metal brackets or straps every 3 to 4 feet so it does not sag or get damaged.

Installing the exterior vent hood

The vent hood is the cap on the outside of your house where the duct exits. It allows air to flow out but prevents rain, snow, and pests from entering. Slide the hood onto the end of the duct, or if the hood has a flange that mounts to the wall, position the duct inside the hood opening and find the hood to the wall with the fasteners it came with — usually screws into wood or anchors into brick or vinyl siding.

Make sure the hood damper (the flap inside) moves freely. When the dryer is off, the damper should hang closed. When the dryer runs, the air pressure pushes it open. If the damper is stuck or missing, replace the hood — a stuck damper traps lint and moisture inside the duct.

Securing and insulating the duct run

Once the duct is in place from the dryer to the outside, go back and check every connection. Tighten the clamp at the dryer again. If there are any joints where two pieces of duct connect, find those with clamps as well. The duct should not move when you push on it.

If the duct runs through an unconditioned space — an attic, crawlspace, or uninsulated wall — consider wrapping it with duct insulation. This prevents condensation from forming inside the duct when warm, moist air hits cold surfaces. Condensation drips back into the dryer and can damage the heating element or create mold. Insulation is not required in most climates, but it is cheap insurance in cold regions.

Testing the connection and what to do if airflow is weak

Before you push the dryer back into place, run a test cycle. Open the dryer door, turn it on, and feel the air coming out of the vent hood on the outside. You should feel a strong, steady flow of warm air. If the flow is weak or barely noticeable, something is blocking the duct.

The most common culprit is a kinked or crushed duct, especially if you used flexible vinyl instead of rigid metal. Check the entire run for bends or damage. The second most common issue is a damper stuck closed on the vent hood — push it open by hand and make sure it swings freely. If the duct is straight and the damper moves, the problem may be lint buildup inside the duct from a previous installation, or the run may be too long for your dryer's blower. If you have more than 25 feet of duct or more than two bends, a booster fan mounted inside the duct can restore airflow.

Frequently Asked Questions

Can I use flexible vinyl duct for a dryer vent?

Flexible vinyl is not recommended for permanent installations. It crushes easily, traps lint in its ridges, and can melt if the dryer runs hot. Use rigid metal or semi-rigid metal duct instead. Flexible duct is acceptable only as a short, temporary connection between the dryer and a wall opening while you install the permanent duct.

What size clamp do I need?

A standard hose clamp or duct clamp sized for 4-inch duct works for most dryers. Bring a piece of your duct to the hardware store and test the clamp around it — it should tighten snugly without gaps. Stainless steel clamps last longer than galvanized steel, especially in damp basements.

Do I need a permit to install a dryer vent?

Many jurisdictions require a permit if you are cutting through an exterior wall or roof. Check with your local building department before you start. If a permit is required and you skip it, you may have trouble selling your house later — the inspector will flag unpermitted work.

How often should I clean the duct?

Clean the duct at least once a year, or more often if you notice weak airflow or the dryer taking longer to dry clothes. Lint accumulates inside the duct and reduces efficiency. You can use a dryer vent brush kit (available at hardware stores) or hire a professional duct cleaning service.

What if my dryer outlet is on the roof instead of a wall?

A roof vent is possible but less ideal than a wall vent because water can pool around the hood and cause leaks. If you must use the roof, buy a roof flashing kit designed for dryer vents — it seals the hole and directs water away. Install it carefully so the flashing sits under the shingles above it and over the shingles below it, like roof shingles overlap.