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 honest answer for Nova Scotia surprises most people: Canada's building code doesn't give a number.

We read the 2020 National Building Code of Canada, which Nova Scotia adopted from 1 April 2025. For a house, it says a dryer's exhaust duct must (Article 9.32.1.3):

• discharge directly to the outdoors,
• be independent of other exhaust ducts,
• be accessible for cleaning, and
• be made of smooth, corrosion-resistant material.

It sets no maximum length. The limit that actually governs your dryer is the one in its installation instructions, which give a maximum run that gets shorter with every elbow you add. Lost the manual? The model number on the door frame will find it on the manufacturer's website.

About the "35 feet" you'll see everywhere: that figure, with 2.5 feet off for each 45-degree elbow and 5 for each 90, comes from the US International Residential Code. It isn't the rule here, and a given dryer's own limit may be longer or shorter. Go by the manual.

The principle underneath any number 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 metal semi-rigid or foil connector made for dryers — never white vinyl or plastic, which is a genuine fire hazard. The code's smooth-duct rule deliberately doesn't cover this connector (the National Building Code's explanatory note says the requirement applies to the ducting within the wall assembly), so the dryer manufacturer's instructions are what govern it.
• 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.

Where the vent can come out (and where it can't)

The outside end is governed by code too. Under the National Building Code (Article 9.32.3.13), exhaust outlets that carry moist air — it names clothes dryer exhaust specifically — must be at least 1,800 mm (about 6 ft) from any air intake and from vented soffits. That rules out two common shortcuts:

• Beside the air exchanger's intake. An HRV that breathes in dryer exhaust is pulling lint and moisture straight back into the house. (Hood placement is covered in our HRV installation cost guide.)
• Up under the eaves. Moist exhaust next to a vented soffit rises into the attic. If the outlet sits in or near a soffit, the code requires that section of soffit to be unvented or blocked.

For a gas dryer, the gas installation code (CSA B149.1) adds its own rules: the duct must terminate outside, be noncombustible or certified as a Class 1 air duct, and stay at least 3 ft (1 m) from any gas pressure-regulator vent or fresh-air intake.

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 fire. The National Building Code's own explanatory notes say it plainly: "Clothes dryers are a major cause of fires in buildings often due to a build-up of lint in the system." Emptying the lint trap every load, and having the duct itself cleaned whenever drying times start to creep up (sooner with pets, heavy use 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 ventilation 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.

Sources

The code references on this page are Canadian, and they're the ones that apply in Nova Scotia. Last verified September 21, 2026.

Canadian sources

• National Research Council of Canada: National Building Code of Canada 2020, free from NRC. Cited: Article 9.32.1.3 (venting of laundry-drying equipment in houses: discharge outdoors; independent, cleanable, smooth, corrosion-resistant duct), its explanatory Note A-9.32.1.3.(2) (the requirement covers ducting in the wall assembly, not the flexible connector), Sentences 9.32.3.13.(4) to (6) (1,800 mm from air intakes and vented soffits; soffit blocking), and Note A-6.3.2.10.(7) and (8) (dryers as a major cause of fires through lint build-up). We searched the whole code for dryer requirements: it sets no maximum duct length.
• Province of Nova Scotia: Province to adopt 2020 National Building Codes, for adoption of the 2020 codes from 1 April 2025.
• CSA B149.1, Natural gas and propane installation code (clauses 7.5.1 and 7.5.2, domestic clothes dryers). CSA B149.1 is a paid standard that we haven't read in full. We cite the two clauses as quoted verbatim by the Government of Alberta in STANDATA 23-BCV-008 (Rev 1), October 2024. That document is an Alberta variance, but the CSA clauses it quotes are national.

What we looked for and couldn't find

• A Canadian code limit on dryer-duct length. There isn't one in the National Building Code. The limit that applies is in the dryer manufacturer's installation instructions.

Non-Canadian reference, named but not relied on

• US International Residential Code: the source of the "35 feet, less 2.5 ft per 45° and 5 ft per 90° elbow" figure that dominates search results. We name it only so you can recognise it. It is not a requirement in Nova Scotia, and this page does not use it as one.