What is the difference between a trunk-and-branch and radial duct layout for Toronto homes?

Trunk-and-branch and radial are the two main duct layout strategies used in GTA homes, and each has distinct advantages depending on your home's floor plan, age, and renovation goals. Understanding the differences helps you have an informed conversation with your ductwork contractor about which approach makes sense for your specific situation.

A trunk-and-branch layout uses a large central trunk line — typically rectangular galvanized steel running down the centre of the basement ceiling — with smaller branch ducts splitting off to serve individual rooms. This is by far the most common layout in GTA homes built from the 1940s through today. The trunk line starts at the furnace plenum at its largest size and gradually reduces as branches take off, maintaining appropriate air velocity throughout the system. In older Scarborough, North York, and Etobicoke homes, you will almost certainly find a trunk-and-branch system, often with a single rectangular trunk running the full length of the basement. The main advantage is simplicity and cost-effectiveness — one large trunk serves the entire home, and individual branches can be added, modified, or balanced independently. The downside is that the trunk line takes up headroom in the basement, typically hanging 8 to 12 inches below the floor joists, which becomes a real issue when finishing a basement where every inch of ceiling height matters.

A radial layout (sometimes called a spider or octopus layout) runs individual ducts directly from a central supply plenum to each room, with no shared trunk line. Each duct is independently sized for its specific room load. This layout is common in modern homes where ducts run through the attic or in slab-on-grade construction, and it is increasingly popular in GTA basement renovations where homeowners want to maximize ceiling height by eliminating the bulky trunk line. Radial systems using round spiral duct or flex duct can be routed between joists rather than hanging below them, preserving valuable headroom. The trade-off is that radial layouts require more total duct material and more plenum connections, which typically costs 15 to 25 percent more than an equivalent trunk-and-branch system — expect roughly $4,000 to $8,000 for a radial system versus $3,000 to $6,500 for trunk-and-branch in a typical 1,500 to 2,000 square foot GTA home.

For most existing Toronto homes, trunk-and-branch remains the practical choice because the infrastructure is already in place, contractors are deeply familiar with the layout, and modifications are straightforward. If you are building new, doing a major gut renovation, or finishing a basement where ceiling height is critical, a radial layout deserves serious consideration. Either way, proper duct sizing using Manual D calculations is essential — the layout matters far less than correct sizing and quality installation with mastic-sealed joints. A well-designed trunk-and-branch system will outperform a poorly sized radial system every time.

When evaluating quotes, ask each contractor which layout they recommend and why, and make sure the proposal specifies duct sizes for every run. If you need help finding qualified ductwork professionals in the GTA, Toronto Ductwork can match you with local contractors for free estimates through the Toronto Construction Network.