What a dryer duct is and why it matters
A dryer duct is the pipe that carries hot, moist air from your dryer to the outside of your home. Without it, that air stays trapped in your laundry room, raising humidity, damaging walls, and making your dryer work harder than it needs to. The duct is not optional—it is the only safe way to run a clothes dryer indoors.
Most dryer ducts are made of flexible aluminum or rigid metal pipe. Flexible ducts are easier to install around corners and obstacles, but they can sag and trap lint if not supported properly. Rigid ducts last longer and resist crushing, but they require more precise fitting. Either way, the goal is the same: a clear, unobstructed path from the dryer outlet to outside air.
Key Takeaways
- A dryer duct connects your dryer outlet to the outside of your home and must be installed before the dryer can run safely indoors.
- Flexible aluminum ducts are common and easier to route, but rigid metal ducts resist lint buildup and last longer if space allows.
- The duct should slope slightly downward toward the outside to prevent moisture from pooling inside the pipe.
- Duct seams must be sealed with metal foil tape, not duct tape or caulk, to withstand heat and prevent air leaks.
- The duct should be as short and straight as possible, with no more than two 90-degree bends, to keep lint from accumulating.
Measuring and planning your duct route
Before you buy materials, trace the path from your dryer to the outside wall. Measure the distance and count how many corners or bends you will need to make. A straight run is ideal, but most homes require at least one turn. Each 90-degree bend adds resistance and makes lint more likely to settle, so plan for no more than two bends if possible.
Check whether your dryer outlet is on an exterior wall or an interior wall. If it is interior, your duct will have to travel through walls, attics, or crawl spaces—this is more complex and may require cutting holes or routing through existing cavities. If the outlet is on an exterior wall, the job is much simpler: the duct runs a short distance straight out through the wall.
Measure the diameter of your dryer outlet. Most household dryers use a 4-inch duct, but some older or compact models use 3-inch. Check your dryer manual or measure the outlet itself before shopping. Buying the wrong size means wasted money and a poor fit that leaks air.
Materials and tools you will need
For a basic installation, gather these items: dryer duct (flexible or rigid, in the correct diameter), a dryer vent hood or wall cap (the outside termination), metal foil tape, hose clamps or duct clamps, a drill or screwdriver, and a utility knife. If your duct runs through walls, you may also need a drywall saw to cut an opening, caulk rated for high heat, and insulation to wrap around the duct where it passes through unconditioned spaces.
Do not use standard duct tape or caulk on a dryer duct. Duct tape degrades in heat and leaves sticky residue inside the duct. Caulk cracks and fails when exposed to the temperature swings a dryer duct experiences. Metal foil tape is the only sealant that holds up to dryer heat and humidity. It costs a few dollars more but is essential.
Connecting the duct to your dryer
Slide the duct onto the outlet port at the back or side of your dryer. The connection should be snug—if the duct is too loose, warm air will escape into the room instead of traveling outside. find the connection with a hose clamp or duct clamp, tightened firmly but not so hard that you crush the duct.
If you are using flexible duct, avoid kinking or sharp bends at the dryer itself. Flex duct can handle gentle curves, but a sharp fold will restrict airflow and trap lint. If your dryer is in a tight corner, you may need to use a short section of rigid duct at the connection point, then transition to flex duct for the longer run.
Seal the connection with metal foil tape, wrapping it around the seam where the duct meets the dryer outlet. Overlap the tape by at least 2 inches and press it firmly to create an airtight seal. This prevents lint and moisture from escaping into the wall cavity.
Running the duct to the outside
If your duct runs along the outside of a wall or through an attic, support it every 3 to 4 feet with a strap or clamp to prevent sagging. Sagging ducts trap lint and moisture, which reduces airflow and increases fire risk. Flexible duct should never be left hanging loose—it will sag under its own weight and the weight of lint buildup.
Slope the duct slightly downward toward the outside, at least 1/4 inch per foot of run. This allows any condensation that forms inside the duct to drain toward the exit rather than pooling inside the pipe or dripping back into the dryer. A level or slightly upward-sloping duct will trap moisture and cause rust or mold inside the duct.
Where the duct passes through a wall, attic, or crawl space, keep it at least 12 inches away from insulation and other combustible materials. Dryer ducts get hot—typically 120 to 160 degrees Fahrenheit—and can ignite nearby materials if they are too close. If the duct must pass through an insulated wall cavity, wrap it with high-temperature insulation rated for dryer ducts.
Sealing joints and connections
Every place where two pieces of duct connect must be sealed with metal foil tape. Overlap the tape by at least 2 inches on all sides of the seam. Press it firmly so no air can escape. If you are using rigid duct sections, the joints are the most common place for leaks, so take time to seal them properly.
Do not rely on hose clamps alone to seal a connection. A clamp holds the duct in place but does not create an airtight seal. The tape does that. explore tape first, then add a clamp for mechanical strength. This two-step approach ensures both a tight fit and an airtight connection.
If you are transitioning from flexible to rigid duct or vice versa, use a connector sleeve or adapter designed for that purpose. Do not try to force one type of duct into another—the fit will be poor and the connection will leak. Adapters are inexpensive and make the transition clean and airtight.
Installing the outside vent hood
At the outside end of the duct, install a dryer vent hood or wall cap. This is a flange that mounts to the exterior wall and directs air and lint outside while preventing rain, insects, and outdoor air from entering the duct. Most hoods have a damper or flapper that opens when the dryer runs and closes when it stops, blocking backflow.
Cut an opening in the exterior wall the size specified by your hood manufacturer—usually 4 to 5 inches in diameter for a 4-inch duct. Slide the duct through the opening and connect it to the hood using metal foil tape and a clamp. find the hood to the wall with the fasteners provided, usually screws or bolts. Seal around the hood with high-temperature caulk to prevent air and water leaks around the edges.
Make sure the hood is installed on a wall that faces away from prevailing winds if possible. A hood facing into the wind can allow wind-driven rain or air to enter the duct. Also may support the hood opening is not blocked by vegetation, snow, or debris—a blocked vent will cause the dryer to overheat and shut down.
Testing and troubleshooting
Before running a full load, turn on the dryer and check for air leaks. Feel along the duct and all connections with your hand—you should not feel warm air escaping. If you do, that connection needs more tape or a tighter clamp. Also check that the outside hood damper opens freely when the dryer runs and closes when it stops.
Run a short test cycle and listen for unusual noise. A whistling or hissing sound usually means air is leaking from a joint. A rattling sound may mean the duct is not supported properly and is vibrating against a wall or stud. Both problems should be fixed before you use the dryer regularly.
If the dryer takes much longer than usual to dry clothes, or if the vent hood damper does not open, the duct may be blocked or kinked. Check the entire run from the dryer to the outside hood. Flex duct can develop kinks if it was bent sharply during installation. Rigid duct can be crushed if something heavy was placed on it. Either way, straighten or replace the damaged section.
Frequently Asked Questions
Can I use regular duct tape to seal my dryer duct?
No. Duct tape fails in the heat and humidity of a dryer duct and leaves sticky residue that traps lint. Use metal foil tape instead—it is rated for high heat and creates a lasting seal. It costs a few dollars more but is the only correct choice.
What is the longest a dryer duct can be?
Most manufacturers recommend keeping the duct run under 25 feet, with 1 foot deducted for each 90-degree bend. A 25-foot straight run is acceptable, but a 20-foot run with two bends is better. Longer ducts restrict airflow and allow lint to accumulate. If your dryer is far from an exterior wall, consider relocating the dryer or installing a booster fan.
Do I need to insulate my dryer duct?
Insulation is not required for ducts inside conditioned spaces like your laundry room, but it is recommended for ducts that pass through attics, crawl spaces, or exterior walls. Insulation reduces condensation inside the duct and helps maintain airflow in cold weather. Use insulation rated for high-temperature ducts, not standard fiberglass batts.
Can I vent my dryer into the attic or basement instead of outside?
No. Venting indoors introduces moisture and lint into your home, which damages insulation, promotes mold, and creates a fire hazard. Dryers must vent to the outside. This is a building code requirement in all jurisdictions and a safety standard set by dryer manufacturers.
How often should I clean my dryer duct?
Clean the duct at least once a year, or more often if you notice the dryer taking longer to dry clothes or the outside hood damper not opening fully. Lint accumulates inside the duct over time and restricts airflow. A clogged duct makes the dryer overheat, shortens its lifespan, and increases fire risk. You can use a dryer vent brush kit or hire a professional duct cleaning service.