Flex hose or rigid duct: what should be behind your dryer

What the ridges do

Rigid metal duct is smooth inside, so lint passing through has nothing to catch on. Corrugated flex hose is a spiral of ridges, and every ridge is a ledge. Lint settles on each one, the effective diameter shrinks, airflow drops — and less airflow means still more settles.

The same length of duct will hold considerably more lint in flex than in rigid, and it will get there faster.

Where it turns up in older houses

Two places, mostly. Immediately behind the dryer, where a short flexible connector is genuinely needed so the appliance can be pulled out. That use is normal and fine.

And running the length of a basement ceiling or up through a chase, where somebody used flex hose because it was easier to work with than rigid duct in a tight old building. That is where it should never have gone, and it is where we most often find a run that is almost entirely closed.

When it is worth replacing

If the long portion of your run is flex, replacing it with rigid metal duct changes how often you need a clean at all, rather than just resetting the clock. We run rigid metal duct and seal it along the basement wall.

If the only flex is the short connector behind the dryer and it is not crushed, it is doing its job and can stay.

• Crushed or kinked flex behind the dryer — replace it; it is restricting the run at its narrowest point.
• Long flex runs through a basement ceiling, chase or crawlspace — worth converting to rigid.
• Flex sagging between supports, which creates a low point where moisture collects.
• Foil flex that has torn, which vents hot moist air into the basement instead of outside.