Dryer Venting Done Right: Length Limits, Safety, and Common Mistakes

Of all the venting in a house, the dryer vent gets the least thought and causes some of the biggest problems. It seems trivial — hook up a duct, done — but the wrong duct, too long a run, or a vent that ends in the wrong place quietly turns into long drying times, wasted energy, and a genuine fire risk. Here's how dryer venting should actually be done, and the mistakes worth fixing.

Where a dryer has to vent

A dryer moves a lot of warm, moist, lint-filled air, and all of it has to go outside — through an exterior wall or the roof, terminating in a proper cap. Not into the attic. Not into a crawlspace. Not "into the basement, it adds humidity in winter." Every one of those relocates moisture and lint into your home, where it causes condensation, mould, and a growing pile of flammable lint.

For a gas dryer it's not just a moisture issue — the exhaust also contains combustion gases, including carbon monoxide, so venting it anywhere but outside is a safety problem, full stop.

How far can a dryer vent run?

This is the question people search most, and for good reason — run length makes or breaks a dryer's performance. The standard guidance limits the total duct run to about 35 feet, and every bend counts against that: roughly 2.5 feet for each 45-degree elbow and 5 feet for each 90-degree elbow. So a run with a few turns can hit its limit at well under 35 feet of actual pipe.

Two important caveats: your dryer's manufacturer may specify a different maximum (often longer for modern dryers with stronger blowers, sometimes shorter), and that spec takes priority; and your local code is the final word. The principle underneath the numbers is simple — the shorter and straighter the run, the better the airflow, the faster clothes dry, and the less lint has a chance to settle and build up.

The right duct — and the wrong ones

Duct choice matters as much as length:

• Best: smooth, rigid metal duct for the main run. Its smooth walls resist lint buildup and move air efficiently.
• The transition behind the dryer should be a short piece of UL-listed semi-rigid or foil duct — never white vinyl or plastic, which is a genuine fire hazard.
• Avoid long runs of ribbed flexible duct: the corrugations trap lint and strangle airflow.
• Joints should be sealed with foil tape, not sheet-metal screws — screws poke into the airstream and snag lint, building a clog from the inside.

Get the duct right and half the common dryer problems disappear on their own.

Signs your dryer vent is clogged

A restricted or clogged vent announces itself if you know the signs:

• Clothes take two cycles to dry, or come out hot but still damp.
• The dryer and the laundry room get very hot, and the room feels humid.
• The exterior vent flap doesn't open (or barely does) when the dryer runs.
• A burning or musty smell during a cycle.

A burning smell is the one to never ignore — stop and get it checked. Restricted airflow makes the dryer run hotter and longer, which is exactly the condition that turns accumulated lint into a fire.

Why lint is the real hazard

Dryer lint is highly flammable, and a restricted vent gives it every chance to collect. As airflow drops, more lint settles in the duct instead of blowing outside; the dryer runs hotter to compensate; and you've built the recipe for a dryer fire — one of the more common and preventable house fires. Routine lint cleaning (typically once a year, more with heavy use, pets, or a long run) is maintenance every household should keep up. Proper venting — smooth duct, the right length, a clean termination — is what makes the whole system safe and easy to keep clean in the first place.

Common mistakes we fix

The problems we see again and again on dryer venting:

• Crushed or kinked flex behind the dryer, choking the run before it starts.
• Runs that are too long or have too many tight elbows.
• Vents terminating in the attic or crawlspace instead of outside.
• No exterior cap or a stuck damper — letting cold air, weather, and pests back in.
• Vinyl or plastic duct, or joints held together with lint-snagging screws.
• A dryer venting into the house "for winter humidity" — never worth the moisture and lint.

None of these are big jobs to correct, and every one of them pays off in faster drying, lower energy use, and a lower fire risk.

Where we fit in

Dryer venting is air-side, sheet-metal work — our trade. We run and re-run dryer exhaust the way it should be: smooth rigid duct on the shortest practical path, sealed properly, and terminated outside with a weather- and pest-rated cap. If your clothes take forever to dry, your laundry room is hot and humid, or you've found your dryer vents into the attic or the house, that's a straightforward fix that makes your dryer work better and your home safer.