A Long Run
Moving the laundry out of the basement is a popular Toronto renovation and the dryer vent is the part that gets solved badly.
Short answer
Every elbow and every metre of duct adds resistance, and there is a maximum equivalent length a dryer can work against. A long run with several elbows means longer drying times, more lint accumulation, more condensation in winter and a higher fire risk. The answers are a shorter route, a booster fan, or a condensing dryer.
Why length matters
A dryer blower is designed to work against a limited resistance, which the manufacturer states as a maximum equivalent length.
Every elbow counts as several metres of straight duct toward that maximum, and a tight elbow counts for more than a sweeping one.
A run beyond the maximum means the dryer cannot exhaust properly, so drying times lengthen and the machine runs hotter.
Slower air deposits more lint along the run, which reduces the diameter and makes it worse — a feedback loop.
In winter, slower air has more time to cool and condense, which is the frozen vent problem.
And the fire risk rises with both the lint accumulation and the operating temperature.
Count the elbows
Add up the straight length and then add the equivalent length for every elbow, and compare it with the figure in the dryer manual. A second-floor laundry venting down and out through a basement wall with five elbows is frequently well over the limit, and that is the real answer to why the loads take two hours.
The options
A shorter route, which is the best answer and which is worth real effort to find during a renovation — straight out through the nearest exterior wall is always better than a tidy route through the house.
Larger diameter duct, which reduces the resistance for the same length.
Sweeping elbows rather than tight ones, and rigid metal throughout.
A dryer booster fan, which is a real product with a real application and which needs a lint-tolerant design and a pressure switch so it runs with the dryer.
A condensing or heat pump dryer, which does not vent at all and which is increasingly the sensible answer for an interior laundry room.
And accepting a longer drying time, which is a legitimate choice as long as the duct is clean and the run is within the manufacturer limit.
What not to do
Do not vent into the attic, the crawlspace, the garage or an interior space to avoid the length. That puts litres of water into the building every load.
Do not use flexible foil duct for a long run, which is the worst case for both lint and resistance.
Do not fit a lint trap box and call the problem solved, which is a last resort where there is genuinely no exterior route.
Do not run the duct through an unheated space without insulating it.
Do not terminate into a soffit, which draws the moist air straight back into the attic.
And do not ignore the drying time, which is the only warning the system gives.
Common questions
How long can a dryer vent be?
The manufacturer states a maximum equivalent length, and each elbow counts as several metres.
Is a booster fan a real solution?
Yes, with a lint-tolerant design and a pressure switch so it runs with the dryer.
What about a condensing dryer?
Increasingly the sensible answer for an interior laundry with no good vent route.