Dryer duct is the 4-inch diameter vent pipe that carries hot, moist, lint-laden air from your clothes dryer to the outside of your home. It is one of the most safety-critical components in residential HVAC — improperly installed or maintained dryer ducts cause an estimated 15,500 house fires per year in the United States, according to the National Fire Protection Association (NFPA).
The good news: choosing the right dryer duct and installing it correctly is straightforward. This guide covers every type of dryer duct hose available, explains when rigid metal is required vs when semi-rigid is acceptable, walks through installation step by step, and summarizes the building code requirements you need to pass inspection.
Types of Dryer Duct
1. Rigid Smooth-Wall Metal Duct (Recommended)
Rigid smooth-wall galvanized steel or aluminum pipe is the gold standard for dryer venting. The smooth interior surface creates minimal airflow resistance, prevents lint accumulation, and provides the highest fire safety. It is the only type allowed inside concealed spaces (walls, floors, ceilings) by the IRC.
Available in 4-inch diameter, 24-gauge galvanized steel or 28-gauge aluminum. Standard lengths: 2-foot and 5-foot sections that snap together with crimped ends. Elbows available in 90° and 45° in both adjustable and fixed configurations.
Pros: Lowest lint accumulation, longest allowable run (35 ft), highest fire resistance, code-compliant everywhere, lasts 20+ years. Cons: Rigid — requires precise routing, harder to install in tight spaces, more expensive than flexible options.
2. Semi-Rigid Aluminum Duct
Semi-rigid aluminum duct is a corrugated aluminum tube that holds its shape after bending. It bridges the gap between rigid pipe and flexible hose — it can bend around obstacles but does not sag or collapse like foil flex duct.
Most building codes accept semi-rigid aluminum for the transition piece between the dryer and the rigid duct system — typically the 1-3 feet immediately behind the dryer where flexibility is needed to push the dryer against the wall. Some codes allow semi-rigid for the entire run if it is UL 2158A listed.
Our semi-rigid aluminum duct is rated to 400°C (752°F) — well above the 150°C maximum exhaust temperature of any residential dryer. Available in 4-inch diameter, 8-foot lengths. For insulation options, code compliance details, and a full comparison with flex and rigid duct, see our insulated semi-rigid duct guide.
Pros: Bends without kinking, holds shape, good fire resistance, UL listed. Cons: Corrugated interior traps more lint than smooth-wall rigid, slightly higher airflow resistance, not accepted for concealed spaces in some jurisdictions.
3. Flexible Foil Duct (Use with Caution)
Flexible foil duct (sometimes called "dryer duct hose") is a thin aluminum foil tube supported by a wire helix. It is lightweight, inexpensive, and easy to install — which is why it is the most commonly used dryer duct in existing homes. However, it has significant drawbacks for dryer venting.
The foil surface crushes easily, creating lint traps. When compressed or bent, airflow drops dramatically. The wire helix can separate from the foil, creating internal obstructions. Most importantly, the thin foil has low fire resistance compared to rigid metal or semi-rigid aluminum.
Many jurisdictions have banned flexible foil duct for dryer venting. California (CRC §M1502.4.1), Oregon, and several other states require rigid or semi-rigid metal only. Even where foil flex is technically allowed, it is limited to the transition piece (max 8 feet) and never inside concealed spaces.
Pros: Cheapest option, easiest to install. Cons: Traps lint, fire risk, sags over time, prohibited in many states, shortest lifespan (2-5 years).
4. Vinyl/Plastic Duct (Never Use)
White or clear vinyl/plastic dryer duct was common decades ago but is now prohibited by all major building codes. Vinyl melts at dryer exhaust temperatures, and the ridged surface is an extreme lint trap. If your home has vinyl dryer duct, replace it immediately — it is a fire hazard.
Dryer Duct Comparison Table
| Type | Fire Safety | Lint Buildup | Max Run | Concealed OK? | Cost/ft |
|---|---|---|---|---|---|
| Rigid smooth-wall | Excellent | Minimal | 35 ft | Yes | $2-4 |
| Semi-rigid aluminum | Good | Moderate | 8 ft (transition) | Some codes | $1-3 |
| Flexible foil | Fair | High | 8 ft max | No | $0.50-1 |
| Vinyl/plastic | Dangerous | Extreme | Prohibited | No | — |
Building Code Requirements (IRC M1502)
The International Residential Code Section M1502 governs dryer exhaust ducts. Key requirements:
Material: Rigid metal duct must be minimum 0.016-inch-thick (28 gauge) galvanized steel or aluminum. Flexible duct, if allowed, must be listed and labeled per UL 2158A.
Diameter: Minimum 4 inches (102mm). Must match the dryer outlet size — never reduce.
Maximum length: 35 feet from the dryer exhaust to the exterior termination point. Deductions: 5 feet per 90° elbow, 2.5 feet per 45° elbow. The dryer manufacturer may specify a shorter maximum — always follow the more restrictive requirement.
Joints: Must be secured with foil tape, UL-listed clamps, or approved sealant. Sheet metal screws are prohibited inside dryer duct — the protruding screw tips catch lint and create blockages. Joints must be installed with the male (crimped) end pointing in the direction of airflow so lint slides past the joint rather than catching on it.
Exterior termination: Must terminate outside the building with a backdraft damper and a cover that opens when the dryer is running. Screen mesh is prohibited at the termination — it catches lint and blocks airflow. Minimum 12 inches above grade.
Concealed ducts: Only rigid smooth-wall metal duct is allowed inside walls, floors, and ceilings. Flexible duct of any type is prohibited in concealed spaces because it cannot be inspected or cleaned without demolition.
Installation Guide
Step 1: Plan the route. The shortest, straightest path to an exterior wall is always best. Every foot of duct and every bend reduces airflow. Calculate your maximum allowable length (35 ft minus elbow deductions) and verify your planned route fits within that limit.
Step 2: Cut the wall penetration. Use a 4-1/4 inch hole saw to cut through the exterior wall for the vent cap. Position the hole at the same height as the dryer exhaust or higher — dryer duct should slope downward toward the exterior to drain condensation.
Step 3: Install the vent cap. Insert the vent cap from outside, secure with screws, and seal around the flange with exterior-grade silicone caulk. Ensure the damper flap moves freely.
Step 4: Assemble rigid duct. Connect rigid duct sections with the crimped (male) end pointing toward the exterior (in the direction of airflow). Secure each joint with foil tape — wrap at least one full revolution around the joint with 2 inches of overlap. Do not use sheet metal screws.
Step 5: Connect the transition piece. Use a semi-rigid aluminum duct for the connection between the dryer and the rigid duct system. This short flexible section (1-3 feet) allows you to push the dryer against the wall without stressing the rigid connection. Secure both ends with worm-gear clamps.
Step 6: Support the duct. Support horizontal runs with metal hangers or straps every 4 feet. Maintain at least 1/4 inch per foot of downward slope toward the exterior. Rigid duct should not rest on ceiling joists or other surfaces that could vibrate and loosen joints.
Step 7: Test. Run the dryer on high heat for 10 minutes. Go outside and verify strong, warm airflow from the vent cap. Check all joints for air leaks — you should feel no warm air escaping at any connection point.
When to Replace Dryer Duct
Replace your dryer duct if any of these conditions apply: the duct is vinyl or plastic (immediate fire hazard), the flexible foil duct is crushed, kinked, or sagging, drying time has increased noticeably despite lint trap cleaning, visible lint is accumulating at the exterior vent cap, the duct has not been cleaned in 3+ years and access for cleaning is limited, or you are remodeling and can upgrade to rigid metal duct.
When replacing, upgrade to rigid smooth-wall metal for the main run and semi-rigid aluminum for the transition. The material cost for a typical 10-foot dryer duct replacement is $20-40. The fire safety and energy efficiency improvement is well worth the investment.
Need dryer duct, semi-rigid aluminum transition duct, or duct accessories for your installation? Browse our flexible duct products or request a quote.