How much energy can I save by sealing leaky ductwork in my Toronto home?

Sealing leaky ductwork in a typical Toronto home can reduce heating and cooling energy consumption by 20 to 40 percent, which translates to roughly $300 to $800 per year in savings on gas and electricity bills at current GTA utility rates. The actual savings depend on how leaky your current ducts are, where the leaks are located, and whether your ducts run through conditioned or unconditioned spaces.

The reason duct leaks waste so much energy is straightforward: your furnace and air conditioner are producing conditioned air, but a significant portion of that air never reaches the rooms you are trying to heat or cool. In a typical older GTA home — particularly the post-war homes built between 1945 and 1975 across Scarborough, North York, and Etobicoke — duct systems can leak 25 to 40 percent of total airflow. That means for every dollar you spend on heating or cooling, 25 to 40 cents is literally leaking into your walls, ceiling cavities, attic, or basement. Your furnace runs longer cycles to compensate, your air conditioner struggles to cool rooms at the end of long duct runs, and your energy bills climb steadily.

The location of the leaks matters enormously. Leaks in ducts running through unconditioned spaces — attics, crawlspaces, and uninsulated garages — are the most expensive because the conditioned air is escaping directly to the outdoors. A supply duct leak in a Toronto attic during January is pushing heated air into a minus 15 degree space, which is pure waste. The same leak in summer pushes cold air-conditioned air into a 50-degree attic. Leaks in ducts within the building envelope — such as basement ceiling ducts in a home with a finished basement above — are less costly because the leaked air at least stays within the conditioned space, though it still causes pressure imbalances and comfort problems.

Return duct leaks are often worse than supply leaks because they pull unconditioned air into the system. A leaky return duct running through an attic pulls hot, humid summer air into your air handler, making your air conditioner work dramatically harder. In winter, it pulls cold attic air into the return, forcing your furnace to run longer. Many older GTA homes use panned floor joist cavities as return air plenums — sheet metal nailed to the bottom of joists — and these are extremely leaky by design, often pulling air from crawlspaces, wall cavities, and even the outdoors.

Professional duct sealing in the GTA costs $1,500 to $4,000 for conventional mastic and foil tape sealing of accessible joints, or $1,500 to $3,500 for Aeroseal treatment that seals from the inside. With annual savings of $300 to $800, most homeowners recoup the investment within three to five years — and the seal lasts the remaining life of the duct system. Beyond energy savings, sealed ducts improve comfort by delivering more air to rooms at the end of duct runs, reduce dust by eliminating gaps that pull particles from wall cavities, and lower humidity problems in summer. If your Toronto home has rooms that are consistently too hot or too cold despite a working furnace and air conditioner, duct leaks are almost certainly a contributing factor.