What is the maximum dryer vent length allowed by code in a Toronto home?

The Ontario Building Code and most dryer manufacturers specify a maximum dryer vent length of 35 feet (approximately 10.7 metres) for a straight, unobstructed run of rigid metal duct, with deductions for every elbow in the run. Each 90-degree elbow reduces the allowable length by approximately 5 feet, and each 45-degree elbow reduces it by approximately 2.5 feet. So a vent run with three 90-degree elbows has a maximum effective length of only 20 feet of straight duct — which is a common constraint in GTA homes where laundry rooms are located in basements or interior rooms far from exterior walls.

This maximum length exists because the dryer's exhaust fan has limited power to push hot, moist air through the vent. When the vent exceeds the allowable length, the fan cannot move exhaust air fast enough, causing lint to settle inside the duct, moisture to condense on duct walls, and drying times to increase dramatically. Over time, the lint accumulation restricts airflow further, creating a compounding problem that eventually becomes a fire hazard. The dryer also overheats because it cannot expel heat efficiently, which accelerates wear on heating elements, thermostats, and the thermal fuse.

To calculate your allowable vent length, start with 35 feet and subtract 5 feet for each 90-degree elbow and 2.5 feet for each 45-degree elbow. Always check your specific dryer manufacturer's installation manual, as some models specify shorter maximum lengths — particularly condensing dryers and compact European-style units popular in Toronto condos. For example, if your dryer manufacturer specifies a 25-foot maximum and your run has two 90-degree elbows, your maximum straight duct length is only 15 feet.

Material matters significantly. The code requires rigid or semi-rigid metal duct (aluminum or galvanized steel) for dryer vents. Flexible vinyl or foil transition duct should only be used for the short connection between the dryer and the wall — never for the vent run itself. Rigid smooth-wall metal duct has much lower airflow resistance than corrugated flex duct, which means the dryer can effectively push air through longer runs. If your current installation uses flex duct for the entire run, replacing it with rigid metal duct can effectively extend your allowable length because the smoother interior surface creates less friction.

In many GTA townhouses and semi-detached homes, meeting the maximum length requirement is genuinely challenging. Laundry rooms in the centre of the home or on upper floors can require vent runs of 20 to 30 feet with multiple direction changes. If your required run exceeds the allowable length, there are a few solutions: install a dryer vent booster fan (an inline fan that assists the dryer's exhaust, typically $200 to $400 installed), relocate the laundry to a position closer to an exterior wall, or switch to a ventless condensing dryer that does not require an exhaust duct at all. A ductwork contractor can assess your specific situation and recommend the best approach — professional dryer vent installation or rerouting in the GTA costs $200 to $800 depending on the run length and complexity.