What is the price to install a fresh air intake duct for a Toronto furnace?

Installing a fresh air intake duct for a furnace in Toronto typically costs $400 to $1,500, depending on the length of the duct run, the type of system being served, and whether make-up air tempering is required. A basic combustion air intake — a dedicated duct bringing outdoor air directly to the furnace room — falls on the lower end, while a tempered fresh air intake integrated with the return plenum costs more.

Every gas furnace in Ontario needs an adequate supply of combustion air to operate safely. In older Toronto homes, combustion air seeped in naturally through gaps in the building envelope — drafty windows, unsealed rim joists, and gaps around doors provided more than enough. But modern energy retrofits that tighten the envelope with spray foam, new windows, and weatherstripping can starve the furnace of air, causing backdrafting that pulls combustion gases — including carbon monoxide — back into the living space. This is a genuine safety hazard and one of the most common issues TSSA inspectors flag in renovated GTA homes.

A direct combustion air intake runs a 6-inch insulated duct from the exterior wall to the furnace or mechanical room. This is the simplest and least expensive option, typically costing $400 to $800 installed. The duct must be insulated where it passes through conditioned space to prevent condensation in winter, and the exterior termination needs a screen and hood to keep out rain, snow, and pests. For homes in lakefront neighbourhoods like Mimico, the Beaches, or Port Credit, extra attention to insulation is important due to the higher ambient humidity.

A fresh air intake tied to the return plenum is a more sophisticated approach that introduces measured outdoor air into the HVAC system's return side, where it mixes with recirculated air before being filtered, heated, and distributed. This method improves indoor air quality throughout the home and is often required in tightly sealed new construction. Expect to pay $800 to $1,500 for this type of installation, which includes a motorized damper, a control to interlock with the furnace blower, and the duct run itself.

If your home has a high-CFM kitchen range hood — anything over 400 CFM — Ontario Building Code requires a make-up air system to replace the exhausted air. This goes well beyond a simple fresh air intake and involves a powered unit with tempering capability to heat incoming air in winter. Make-up air systems cost $2,000 to $5,000 installed and must be interlocked with the range hood so they operate simultaneously.

Any work involving gas appliance connections or modifications to combustion air supply must be performed by a TSSA-registered contractor — this is Ontario law, not a suggestion. The installer should also verify that the fresh air intake does not create negative pressure problems with other combustion appliances like water heaters or fireplaces. Get at least three quotes and confirm TSSA registration and WSIB coverage before hiring. Toronto Ductwork can help you find qualified local professionals through the Toronto Construction Network.