How do I know if my flex duct is crushed or kinked in my Toronto home?

The telltale signs of crushed or kinked flex duct are weak airflow at the affected register, a room that never reaches the right temperature, and sometimes a whistling or hissing sound near the restriction. Flex duct problems are extremely common in GTA homes built from the 1970s through the 2000s, particularly in Mississauga, Brampton, Markham, Vaughan, and Richmond Hill where flex duct was widely used for branch runs in attic and basement ceiling installations.

The simplest diagnostic test is the airflow comparison. Hold your hand in front of every supply register in your home while the system is running. If one or two registers have noticeably weaker airflow than the others — and the damper on that branch is fully open — there is likely a restriction in that duct run. You can make this test more precise by holding a tissue or light piece of paper near the register face. Strong airflow will hold the tissue firmly against the grille, while a restricted run will barely move it.

If you can access your ductwork visually — in an unfinished basement ceiling, crawlspace, or attic — look for these specific problems. Sagging flex duct hangs down between support points like a hammock, creating low spots that restrict airflow and collect condensation. Flex duct should be supported every four feet maximum with broad saddle-type hangers — never with wire or string that cuts into the duct and creates pinch points. Kinked flex duct has sharp bends where the inner wire helix has collapsed, creating a near-total blockage. This commonly happens at turns around framing members, at connections to register boots, and where the duct drops from an attic floor to a ceiling register. A 90-degree kink can reduce airflow by 50 percent or more. Crushed flex duct occurs when heavy items are stored on top of duct runs in attics, when insulation is packed too tightly around ducts, or when someone has stepped on a duct while working in the attic.

Flex duct that is not pulled taut is also a performance problem even if it is not technically kinked. The corrugated inner liner of flex duct creates significant friction when the duct is compressed or bunched. A six-foot section of flex duct that is only stretched across a four-foot span has far higher friction than the same duct pulled taut. Industry standards require flex duct to be stretched to at least 90 percent of its full extended length.

If you find crushed or kinked flex duct in your basement, the repair is relatively straightforward — reposition the duct to eliminate the kink, support it with proper hangers every four feet, pull it taut, and re-secure connections with zip ties and mastic. Replacement flex duct costs $3-$8 per linear foot for material. However, if the damaged flex duct is in an attic, hire a professional. GTA attics are extreme work environments, and improper flex duct repair in an attic — particularly leaving gaps in the vapour barrier — creates condensation problems that cause mould and water damage. Professional flex duct repair or replacement for a single run typically costs $200-$600 in the GTA market. If multiple runs are damaged, it may be more cost-effective to replace all attic flex duct with properly supported and insulated rigid metal duct, which is more durable and has lower friction for better airflow.