What is the price for removing and replacing octopus furnace ductwork in a Toronto home?

Removing and replacing octopus furnace ductwork in a Toronto home typically costs $8,000 to $18,000 for the complete project, including demolition of the old gravity system, asbestos testing and possible abatement, design and installation of a modern forced-air duct system, and connection to a new high-efficiency furnace. This is one of the most transformative upgrades available for owners of pre-war Toronto homes.

Octopus furnaces — named for their large, tentacle-like ducts radiating from a central firebox — were standard in Toronto homes built before 1945. You will find them in neighbourhoods like the Annex, Cabbagetown, Riverdale, High Park, Roncesvalles, the Danforth, and older sections of East York and York. These gravity-fed systems relied on natural convection: hot air rises through oversized round ducts to upper floors, while cooled air falls back down through return openings near the floor. There is no blower motor, no filter, and no air conditioning capability. The ductwork is typically large-diameter round galvanized steel — 10 to 16 inches — running vertically through walls and horizontally across basement ceilings.

The replacement project breaks down into several phases. Asbestos testing should be done first, as virtually all octopus furnace systems used asbestos-containing insulation, tape, or cement at duct joints and around the firebox. Testing costs $300 to $600, and if asbestos is confirmed — which it almost always is — professional abatement adds $2,000 to $5,000 depending on the extent. Never disturb an octopus furnace system without testing first.

After abatement, the old ductwork is removed. This creates an opportunity to redesign the entire distribution system using modern Manual D duct sizing calculations. The new system will include a properly sized supply plenum, trunk lines (typically 8-inch to 12-inch rectangular or round), branch runs to each room, return air ducts from every floor, and a filter rack. Material and installation for the new ductwork in a typical two-storey, 1,200 to 1,800 square foot Toronto home runs $5,000 to $10,000. Adding the new furnace — which is almost always part of this project, since octopus furnaces cannot be converted — adds $3,500 to $6,500 for a mid-efficiency to high-efficiency gas unit installed by a TSSA-registered contractor.

One challenge specific to octopus furnace replacements in Toronto's older homes is that the original oversized duct chases through walls and floors are larger than what modern ductwork needs, while the modern system requires supply and return runs to rooms that the gravity system never served directly. Creative routing is often necessary — experienced ductwork contractors familiar with Toronto's older housing stock know how to use existing chases, add soffits where needed, and minimize drywall disruption.

The total project — asbestos abatement, old system removal, new duct design and installation, new furnace, permits, and inspections — runs $10,000 to $18,000 for most Toronto homes. It is a significant investment, but the result is transformative: even heating and cooling to every room, proper air filtration, air conditioning capability, dramatically lower energy bills, and elimination of a system that may have been producing elevated carbon monoxide levels for years. City of Toronto building permits are required and cost $400 to $800 for the mechanical work. Get matched with experienced local ductwork contractors through Toronto Ductwork and the Toronto Construction Network.