Is flexible foil dryer duct safe to use?

No, and the white plastic or vinyl accordion type is worse. Codes and dryer manufacturers call for smooth-wall rigid metal duct, because the ribbed interior of accordion duct catches lint on every ridge and the flexible body sags, crushes and kinks behind the appliance. The only place flexible duct belongs is the short transition between the dryer and the wall, and even there it has to be a listed transition duct, exposed, and never run inside a wall or ceiling.

How long can a dryer vent run be?

The residential code as adopted in Florida sets a 35 foot maximum developed length, and you deduct 2.5 feet for every 45 degree bend and 5 feet for every 90 degree bend. So a run with two 90 degree elbows has an effective allowance of 25 feet of straight duct. If the dryer manufacturer specifies something different, their number governs. Shorter and straighter is always better than merely legal.

What are the signs my dryer vent is blocked?

Clothes that need two cycles to dry, laundry that comes out hot rather than warm, a laundry room that heats up while the dryer runs, and a burning or musty smell. Go outside while the dryer is running and look at the exterior hood: the flap should be pushed open by a steady stream of warm air. If it is barely moving or not moving at all, the duct is restricted.

How often should a dryer vent be cleaned?

At least once a year for a typical household, and more often if the run is long, if there are several people in the house, or if you have pets that shed. Clean the lint screen after every single load, which is a separate habit and the single most effective one. If drying times have crept up over a few months, clean it now rather than waiting for the anniversary.

Should I put a screen on my dryer vent to keep pests out?

No. Codes specifically prohibit screens on a dryer exhaust termination, because a screen catches lint and blocks the vent, which is exactly the hazard you are trying to avoid. The right answer is an exterior hood with a backdraft damper that actually closes, or a louvered hood designed for dryer exhaust. If lizards or wasps are getting in, the damper is stuck open or broken, and the fix is a new hood.

Can I vent a dryer into the garage or attic?

No. A dryer exhaust must terminate outdoors, full stop. Venting into a garage, attic, crawl space or soffit dumps warm, wet, lint-laden air into an enclosed space, which in the Florida climate is a reliable way to grow mold and to build a lint pile next to whatever else is stored in there. A gas dryer vented indoors also releases combustion products where people breathe them.

Dryer vent safety: duct material, runs, and lint cleaning

Clothes dryers are a recognized cause of house fires, and fire investigators consistently point at the same contributing factor: failure to clean. I am not going to quote you a percentage, because the numbers that circulate online are almost always mangled versions of one report. What matters is the mechanism, and the mechanism is simple enough that once you understand it you will never neglect a vent again.

Lint is finely divided cellulose fiber. It is one of the most readily ignitable things in your house. A dryer produces a heat source and a continuous supply of it, and the vent is the only thing carrying both the lint and the heat outside. Restrict that vent and the dryer runs hotter, runs longer, and cycles its high-limit thermostat over and over while lint accumulates around the heat. That is the whole story.

Why the duct material matters more than anything else

Walk behind most dryers in South Florida and you will find one of two things: a silver foil accordion hose, or a white plastic accordion hose. Both are wrong, and the plastic one is genuinely dangerous.

Here is why the ribs matter. Smooth-wall rigid metal duct gives lint nothing to hold onto, so the airflow carries it out. Accordion duct has a ribbed interior, and every single ridge is a shelf. Lint catches, builds, and narrows the pipe from the inside. You cannot see any of it.

Then there is the physical behavior. Flexible duct sags between supports, which creates low spots where lint and condensed moisture collect. It crushes flat when you push the dryer back against the wall. It kinks at every turn. A 4 inch duct crushed to 2 inches is not a 4 inch duct any more.

Duct type	Allowed	Why
Rigid smooth-wall metal, 4 in	Yes. This is the standard	Smooth interior, holds its shape, joints can be properly sealed
Semi-rigid metal	Only as a listed transition duct, exposed	Smoother than accordion foil and holds shape better, but still not for concealed runs
Flexible foil accordion	Only as a listed transition duct, exposed, and better avoided	Ribbed interior traps lint, sags, kinks, crushes
White vinyl or plastic accordion	Never	Combustible, and long since prohibited for dryer exhaust

The transition duct is the short piece connecting the back of the dryer to the wall fitting. That is the one place flexible material is permitted, and only when it is a duct listed and labeled for the purpose. It has to stay exposed, it is limited in length, and it may never run inside a wall, floor or ceiling. Everything from the wall onward is rigid metal.

Assembly details that get missed

Point the joints in the direction of airflow. The male end of each section goes downstream, so lint slides past the joint instead of catching on the lip.
No screws through the duct. Sheet metal screws that protrude into the airstream act like lint hooks and defeat any brush you push through later. Use foil tape, and use clamps where you need mechanical connection.
Foil tape, not cloth duct tape. Cloth duct tape dries out, loses adhesion and falls off inside a wall where you will never see it happen.
Support long horizontal runs so the duct does not sag between joists.

Keeping the run short and the turns few

The residential code as adopted in Florida sets a 35 foot maximum developed length, with 2.5 feet deducted for each 45 degree bend and 5 feet deducted for each 90 degree bend. Other jurisdictions and older code editions differ, so check locally if you are outside Florida. And if the dryer manufacturer specifies a different maximum, theirs governs.

Run configuration	Allowance used by bends	Straight duct remaining
No bends	0 ft	35 ft
One 90 degree elbow	5 ft	30 ft
Two 90 degree elbows	10 ft	25 ft
Four 90 degree elbows	20 ft	15 ft
Two 90s and two 45s	15 ft	20 ft

Treat that as a legal ceiling, not a target. Every elbow costs airflow, and every foot of duct is a foot of surface for lint to settle on. The shortest, straightest route outside is always the right one, even if it costs more to install.

A very common South Florida arrangement is a laundry closet or a garage wall where the dryer sits with a long run up into a hot attic and across to a roof or gable termination. Those runs are the ones that clog, because they are long, they have turns, and nobody ever looks at them.

The periscope duct

If your dryer sits so close to the wall that the transition duct is crushed flat behind it, the answer is a periscope duct. It is a rigid rectangular telescoping section, only a couple of inches deep, that connects the dryer outlet to a wall fitting that may be offset up, down or sideways.

It solves two problems at once. It lets the dryer sit within an inch or two of the wall, and it replaces the crushed accordion hose with rigid smooth-wall metal. If your laundry is in a tight closet, this is the single best upgrade you can make.

Match the periscope’s offset range to the actual distance between your dryer outlet and the wall opening before you buy, because they come in several travel ranges.

Symptoms of a restricted vent

You do not need instruments. You need to pay attention to four things.

Drying times have crept up. This is the earliest and most reliable sign. A load that used to take one cycle now takes one and a half, or two. People adapt to this gradually and never notice.

The laundry is hot, not warm, at the end of the cycle. Properly vented, a finished load comes out warm and dry. If it comes out genuinely hot and slightly damp, moist air is not leaving the drum.

The room heats up while the dryer runs. All the heat the dryer produces is supposed to go outside. If the laundry room or garage is noticeably hotter after a load, that heat is coming out somewhere it should not, usually through a disconnected or leaking duct.

No flap movement at the exterior hood. Start a load on high heat, walk outside, and look at the vent hood. The damper flap should be held open by a steady flow of warm air you can feel with your hand. Barely open, fluttering, or closed means the run is restricted.

Other tells: a burning smell during operation, lint appearing around the door seal or on top of the dryer, a musty smell in clothes because moisture is not leaving, and auto-sensor cycles that shut off early with the clothes still damp.

If your dryer is gas fired, a blocked vent is more than a fire risk. It can push combustion products back into the room. Working carbon monoxide alarms are cheap and you should have them regardless.

How to clean a dryer vent

Annually at minimum. More often with a long run, a big household, or pets.

The lint screen, first

Clean the screen after every load. This is the highest-value thirty seconds in laundry.
Every few months, wash the screen with hot water, a little dish soap and a soft brush. Fabric softener and dryer sheets leave an invisible film that blocks airflow through the mesh.
Test it: run water onto the clean screen. It should pass straight through. If it beads up or pools, there is a film and it needs washing.
Vacuum out the lint screen housing itself with a narrow crevice tool. A surprising amount collects down in that slot.

The duct

Kill the power. Unplug an electric dryer. For a gas dryer, unplug it and shut the gas valve, and do not disconnect the gas line itself. Gas connections are licensed work.
Pull the dryer out far enough to work behind it. Do not stretch or twist the gas connector.
Disconnect the transition duct from the dryer outlet and from the wall fitting.
Vacuum the dryer outlet and everything you can reach behind the appliance. Lint accumulates on the floor and against the back panel.
Run a rotary lint brush kit through the duct. These are flexible rods that couple together with a brush head on the end and chuck into a drill. Feed it in, run the drill in the direction the kit specifies so the sections do not unscrew, and work it through in stages.
Work from both ends where you can, inside and outside. The exterior end usually holds the worst of it.
Replace the transition duct with a listed rigid or semi-rigid piece if what you pulled off was foil or vinyl accordion.
Reconnect everything, clamp it, and run the dryer on air-fluff for a few minutes while you check outside that the flap is moving properly.

If the duct run is long, goes through an attic, or you cannot get a brush through it, that is a job for someone with a proper powered rotary system and a vacuum. Pushing a brush at a blockage you cannot reach can pack it tighter.

The exterior hood and the pest question

The termination matters as much as the duct.

A dryer exhaust must terminate outdoors, always, with a backdraft damper so outside air, rain and pests cannot come in when the dryer is off. Never terminate into an attic, garage, crawl space or soffit. In this climate, dumping warm humid air into an enclosed space is a mold problem waiting to happen, and the lint pile is a fire problem waiting alongside it.

Keep the termination clear of windows, doors and air conditioning intakes, and where it will not blow lint into a neighbor’s screened porch.

Now the pest question, which comes up constantly in Florida, because geckos, wasps and mud daubers all find dryer vents attractive.

Do not put a screen on it. Codes specifically prohibit screens on a dryer exhaust termination, and the reason is exactly the hazard we have been talking about: a screen catches lint until it blocks completely. A well-meaning screen is one of the more common causes of a badly restricted vent.

The correct approach:

Use a hood designed for dryer exhaust with a damper flap that closes fully under its own weight when the air stops. That is the pest barrier.
If pests are getting in, the damper is stuck, warped or missing. Replace the hood rather than screening it.
Louvered hoods with several small flaps also work and stay cleaner than a single large flap on some installations.
Inspect the hood at least annually. Clean lint off the flap and the hinge so it seals.
Near the coast, salt air corrodes cheap painted steel hoods and seizes the hinge. Spend the extra few dollars on a better-quality hood, and check it when you check everything else before hurricane season.

Safety and when to stop

Unplug the dryer before you work behind it. It is a heavy appliance with a heating element in it.
On a gas dryer, do not disconnect, move or work on the gas connector. Moving a gas dryer far enough to strain a flexible connector is a real risk. Gas work is licensed work in Florida.
Never operate a dryer with the vent disconnected, even briefly. Electric dryers dump heat and lint into the room. Gas dryers dump combustion products.
If the duct inside a wall or attic is plastic or vinyl accordion, it needs replacing, not cleaning. That means opening up the run.
If there is scorching, melted plastic or a burnt smell inside the duct or at the dryer outlet, stop using the dryer and get it looked at properly.
If you find the vent terminating into an attic or soffit rather than outside, do not just extend the flexible hose. That run needs to be built correctly in rigid metal.
Working in a South Florida attic in summer is genuinely dangerous. Heat exhaustion is not a joke up there. Early morning only, water with you, and someone in the house who knows where you are.

Adding a dryer vent through a wall that does not have one is a bigger job than it sounds, especially on the concrete masonry unit walls most homes here are built with. It means core drilling through block and properly sealing the penetration, and if you are in a condo, it means association approval for a new exterior penetration. The same considerations apply as with venting an over-the-range microwave.

Put it on the calendar

The reason dryer vents get neglected is that nothing about them is visible. Nobody wakes up and thinks about the duct.

Tie it to something you already do. Clean the vent when you run through your hurricane prep at the start of June, since you are already checking exterior openings, or when you change the smoke alarm batteries. Once a year, on a date you will remember.

When it’s worth calling someone

Cleaning a short, straight run behind a dryer is a genuine homeowner job and a brush kit costs less than a service call. A long attic run, a roof termination, a duct that turns out to be vinyl inside a wall, or a vent that needs to be built where none exists is where it gets worth handing off. I do appliance installation and dryer vent work throughout Broward, Palm Beach and north Miami-Dade, and I will tell you straight if what you have needs replacing rather than cleaning.

Anything involving the gas line itself goes to a licensed pro, and that is not me being cautious for the sake of it.