How Long a Dryer Vent Run Should Be, and Why Bends Count Against It

Two houses on the same street, both with the laundry against an outside wall, can have dryer runs
that behave nothing alike. The reason is usually not length on its own.

What the codes say, and what they do not

The International Residential Code sets a maximum developed length for a dryer exhaust
duct — 35 feet in recent editions — and requires that maximum to be reduced by a specified amount for
each bend in the run. The
International Code Council publishes
the current text.

Two caveats matter and both are real. Jurisdictions adopt different editions at different times, so
the figure that applies to your property is the one your jurisdiction has adopted. And the appliance
manufacturer’s installation instructions apply alongside the code — where they are more restrictive,
they are what governs.

We are not the right people to tell you which edition your county is on. We are the right people to
tell you what the run in your house is actually doing.

Why bends cost so much

Air moving through a duct loses energy to friction along the wall, and loses considerably more
every time it has to change direction. A 90-degree elbow forces the whole airflow to turn in a very
short distance; the air on the inside of the turn slows dramatically, and slow air does not carry
lint.

That is the mechanism the code deduction is standing in for. It is not a bureaucratic penalty — it
is an acknowledgement that a bend behaves like several feet of extra duct as far as the air is
concerned.

Where lint actually settles

• Immediately after each bend, on the inside of the turn
• Along any horizontal section, where gravity is working against the airflow
• At every transition between duct sizes or materials
• At the termination, if the flap no longer opens fully

What this means for how the run performs

A long run with bends starts at a disadvantage and loses ground faster, because the lint that
settles narrows the duct, and a narrower duct moves air more slowly, and slower air deposits more
lint. It is a loop that tightens.

Which is why the first symptom is almost always drying time — see
dryer vent warning signs worth acting on — and why a run that
was fine for years can decline noticeably over one season.

What we do about it

A dryer vent cleaning clears the line along its full
length, from both ends where the layout allows, and checks the termination — the far end being the
part most often skipped and most often the restriction. Airflow is checked at the outlet before and
after, because the number that matters is whether air is actually moving.

Where the geometry is the problem rather than the accumulation, we say so. A run that will load
again in six months is a run that needs a conversation about the duct, not a booking every six
months.

What is worth knowing about your own run

Where it terminates, roughly how far that is from the dryer, and how many direction changes it makes
on the way. Most people know the first, guess the second, and have never counted the third — and the
third is the one that explains the most.