Where do take-off collars go on Toronto trunk ducts?

Take-off collars connect branch ducts to the trunk duct at the point where conditioned air needs to be diverted toward a specific room or zone — they are the junction between the main distribution highway and the individual branch runs serving each supply register.

In a typical GTA home, the trunk duct runs horizontally along the basement ceiling (or through the attic in newer suburban builds), and take-off collars are cut into the trunk at calculated intervals along its length. The collar itself — usually a round fitting with a crimped end for flex duct or a slip connection for rigid round branch duct — gets fastened directly into a hole cut in the trunk wall, then sealed with mastic and UL 181 foil tape before the branch duct is connected.

Placement Along the Trunk

Positioning take-offs correctly along the trunk is not guesswork — it follows the duct design (Manual D) and the pressure profile of the system. Take-offs closest to the air handler (furnace or air handling unit) see the highest static pressure and velocity, so branch runs near the plenum need to be sized and positioned carefully to avoid over-delivering air to nearby rooms while starving rooms at the far end of the trunk. A common approach in GTA homes is to offset the first take-off at least 18–24 inches from the supply plenum to allow airflow to stabilize before the first branch draw-off.

From there, collars are spaced according to the CFM demand of each room they serve. A bedroom needing 80 CFM gets a 5- or 6-inch collar; a living room needing 150 CFM might get a 7- or 8-inch collar or a pair of 6-inch collars. The spacing between collars also matters — crowding multiple take-offs too close together on the same side of the trunk creates turbulence and uneven pressure distribution. A minimum of 12 inches between adjacent collars is a standard rule of thumb, though more separation is always better.

Which Side of the Trunk

Take-offs are typically placed on the bottom or sides of the trunk, not the top. Bottom-of-trunk collars work well for floor registers (very common in post-war Scarborough, Etobicoke, and North York homes with basement-run trunks). Side collars are used when branch runs need to travel horizontally to wall registers or when the branch needs to rise up through a wall cavity. Top-of-trunk collars are generally avoided because they can trap air pockets and are harder to seal properly.

In older GTA homes with rectangular trunk ducts, take-off collars are often spin-in fittings — a round collar with a built-in damper blade that gets spun into a round hole cut in the trunk face. These are excellent because the integral damper lets you balance airflow at each branch without adding a separate damper downstream. For new installations, spin-in fittings with adjustable dampers are strongly recommended — they make balancing a multi-room system dramatically easier.

GTA-Specific Considerations

In post-war Toronto homes where the original duct system was heating-only and air conditioning was added later, you will often find take-off collars that are too small for modern cooling airflow requirements. Cooling needs roughly 400 CFM per ton of cooling capacity, compared to about 300 CFM per ton for heating — meaning the original branch sizing may be 25% undersized for cooling. If your home has uneven cooling with some rooms always warm in summer, undersized take-off collars and branch ducts are a likely culprit.

All take-off collar connections must be mechanically fastened with sheet metal screws (minimum three screws per collar) and sealed with duct mastic before any tape is applied. This is the single most common leak point in residential duct systems — a poorly sealed take-off collar can dump 15–25% of the branch's airflow into the basement or attic instead of the room it is meant to serve.

Need help finding a ductwork contractor to assess your trunk and branch layout? Toronto Ductwork can match you with a local professional for a free estimate — find contractors through the Toronto Construction Network at torontoconstructionnetwork.com/directory?trade=hvac.