AZ Dryer Pros · October 15, 2026
Any duct hidden inside a wall, ceiling or attic should be rigid metal with a smooth inside. The short hose between the dryer and the wall (the transition duct) can be flexible, but it has to be metal, listed for dryers, no longer than 8 feet and not hidden in the wall. Replace the hose if it's plastic, crushed, torn or full of lint.
Two different parts of the vent
A dryer vent has two parts, and the rules differ.
The exhaust duct is the fixed run inside the wall, ceiling or attic that carries air to the outside. The transition duct is the short connector behind the dryer that joins the dryer to that fixed run. Most of the questions about foil and semi-rigid are really about the transition duct.
The hose takes the most abuse of any part of the vent. It gets pushed, bent and stepped on every time the dryer moves, and it sits where lint collects first. In many older homes it's also the one piece nobody has replaced since the dryer was installed.
The fixed duct: rigid metal
The International Residential Code requires the exhaust duct to be metal with a smooth inside, at least 0.016 inch thick, and 4 inches in diameter. In practice, that means rigid metal pipe.
A few related rules matter when we inspect or install:
- Joints run in the direction of airflow, so lint slides past instead of catching
- Screws shouldn't stick into the inside of the duct, where they snag lint
- Flexible hose should never be used as the hidden part of the run
The transition hose: what's allowed
Under the 2015 and 2018 IRC, the transition duct must be a single length, listed and labeled to UL 2158A, no longer than 8 feet, and not concealed inside a wall or ceiling. UL 2158A covers flexible high-temperature dryer connectors, and listed products are marked on the duct.
Here's how the common types compare:
- Foil flex: light and easy to fit. Some foil products are listed to UL 2158A. It crushes easily, and the ridges catch lint, so it needs more attention.
- Semi-rigid aluminum: holds its shape better and resists crushing. It's what we usually install behind the dryer. Some dryer manufacturers specify it; check that the product is suitable for your setup.
- Rigid metal: the smoothest and most durable, but hard to fit in the tight space behind a dryer.
- White vinyl or plastic: not acceptable. Fire safety guidance calls for rigid or flexible metal venting.
When to replace the hose
Pull the dryer out and look. Replace the hose if:
- It's plastic or vinyl
- It's crushed, kinked, flattened against the wall or coiled up like a spring
- It's torn or has holes
- It's longer than it needs to be and sags with lint in the low spots
- It's been patched with tape
- You can't tell when it was last replaced and it's coated inside with lint
What a replacement costs
Transition hose replacement starts at $149. We fit the shortest hose that works with your dryer's position and leave room so it isn't crushed when the dryer goes back. If the fixed duct inside the wall is crushed, split or disconnected, that's a repair, from $299. Either way, you get the price first.
Related: Transition Hose Replacement · Prices