Enter your current leakage from a duct blaster test, or use the slider to estimate. Typical existing Canadian homes: 15–30%. Use 20% if unknown.
Detailed Savings Analysis
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How to Use the Duct Sealing Savings Calculator
Where your ducts run drives the cost of leakage. Attic ducts are worst (leaked air is lost outdoors entirely); basement ducts lose less since the leaked air partially heats the space above. The calculator applies a location factor from 1.0 (conditioned basement) to 1.6 (attic) to account for this.
If you don't have a duct blaster test, use 20% for pre-2000 homes, 15% for 2000s builds, 10% for post-2010. After professional mastic sealing, expect 5-8%; Aeroseal can reach 2-4%. CHBA Net Zero targets Qn25 of 4% or less.
Select your city for accurate HDD/CDD, then your fuel rate. Natural gas averages $0.30-0.40/m3, electricity $0.10-0.17/kWh depending on province. Compare fuels with the fuel cost comparison tool.
DIY mastic/foil tape on accessible ducts runs $150-$400 in materials; professional mastic sealing $800-$2,000; whole-system Aeroseal $1,500-$3,500. Check provincial and utility weatherization programs; some include duct sealing rebates now that the federal Greener Homes Grant and Loan have closed to new applicants.
Duct Leakage in Canadian Homes: How Much Does It Cost and How Do You Fix It?
Duct leakage is one of the most overlooked sources of energy waste in Canadian homes. While building envelope air leakage gets attention through blower door testing and air sealing programs, the duct system often receives much less scrutiny, despite leaking 15-30% of conditioned air in a typical existing home. In a cold Canadian climate, this translates directly to higher fuel bills and uneven room temperatures.
How Duct Leakage Works
A forced-air HVAC system moves conditioned air from the air handler to supply registers through supply ducts, and returns air from the house back to the air handler through return ducts. Any gap, poorly connected fitting, or unsealed penetration in these ducts allows conditioned air to escape (supply leakage) or allows unconditioned air to enter (return leakage). Supply leakage in an attic is the worst case: you're paying to heat or cool air and then dumping it into a space that's 30-40°C hotter in summer or -20°C in winter. Return leakage in an attic draws dusty, unconditioned attic air directly into the air handler. Undersized or poorly laid-out ducts make leakage worse by forcing higher static pressure through the system; the duct sizing calculator checks whether existing trunk and branch sizes are adequate before or after a sealing project.
In addition to energy losses, duct leakage causes pressure imbalances that can make rooms uncomfortably cold or hot, create negative pressure that pulls combustion gases back through gas appliances (backdrafting), and distribute attic dust, fibres, and allergens throughout the home. These comfort and air quality impacts often motivate duct sealing as much as the energy savings.
What Duct Leakage Testing Shows in Canada
A duct blaster test pressurizes the duct system to 25 Pa (Qn25) while the house is at the same pressure, isolating duct leakage from building envelope leakage. Research by NRCan and the Canadian Home Builders Association (CHBA) has found that typical existing Canadian homes have duct leakage rates of 15-30% of total system airflow. Newer construction (post-2010) tends to be somewhat better at 10-20%, but duct sealing is rarely required by code and inspection. The CHBA Net Zero Home Labelling Program requires Qn25 of 4% or less, achievable with careful duct construction and full mastic sealing at every joint.
Sealing Methods: Mastic, Foil Tape, and Aeroseal
Three methods dominate duct sealing in Canada. Water-based mastic sealant applied by brush to every joint and connection is the gold standard for accessible ductwork. It remains flexible, doesn't shrink over time, and bonds permanently to sheet metal, fibreglass, and flex duct. It must be reinforced with fibreglass mesh tape on gaps larger than about 6 mm. UL 181-listed foil tape (not generic duct tape, which fails within 1-2 years) is used for tight joints. Together, mastic and foil tape can achieve less than 5% leakage on accessible ductwork. For concealed ducts in walls, ceilings, or finished spaces, Aeroseal injection is the practical option. The pressurized aerosol sealant finds its own way to leakage points from the inside, sealing gaps up to about 12 mm without any access to the exterior of the duct.
Duct Sealing and Equipment Sizing
Significant duct leakage effectively reduces system capacity: the air handler is moving air, but some of it never reaches the conditioned space. A system with 25% duct leakage is operating as if it's 25% undersized. After sealing, the effective capacity increases, which can make existing equipment feel oversized, potentially improving efficiency by allowing longer, lower-speed run cycles. In some cases, duct sealing allows downsizing at equipment replacement. For equipment sizing analysis, use the heat load calculator.
Frequently Asked Questions
Leaky ductwork typically wastes 20-30% of heating and cooling energy when ducts run through unconditioned spaces like attics or unheated crawlspaces. For a typical 185 m² Toronto home with a base heating cost of roughly $1,000-$1,050/year, 20% duct leakage in an unconditioned attic wastes an additional $230-$270/year in heating energy. In colder cities like Edmonton or Calgary, the same leakage rate wastes roughly $370-$400/year. Conditioned basement ducts lose less because leaked heat partially warms the basement and lower floors.
A duct blaster test is the standard method. The duct system is sealed at all registers with covers, then pressurized (or depressurized) to 25 Pa using a calibrated fan. The airflow required to hold that pressure is the Qn25 value, expressed as CFM25 per 100 ft² of conditioned floor area. A Qn25 under 4 CFM25/100 ft² is the CHBA Net Zero target. Typical existing Canadian homes test at 10-25 CFM25/100 ft². The duct blaster test can also be done at 50 Pa (Qn50), and it's often bundled with a blower door test as part of an NRCan EnerGuide home evaluation to measure total leakage to outdoors specifically.
Yes, in most cases. For homes with ducts in unconditioned spaces and leakage above 15%, duct sealing almost always delivers a simple payback of 3-7 years and significant comfort improvements. Professional mastic sealing costs $800-$2,000 and reduces leakage by 50-70%. DIY sealing of accessible ducts with mastic and UL 181 foil tape costs $150-$400 and can achieve similar results for accessible sections. Benefits beyond energy savings include more even room temperatures, better indoor air quality (less attic dust), and reduced equipment runtime and wear.
Some provincial programs include duct sealing in their weatherization incentive packages. BC's CleanBC Better Homes program and some Ontario municipal programs cover duct sealing. The federal Canada Greener Homes Grant previously covered duct sealing as part of a broader retrofit package, but both the Grant and the follow-on Greener Homes Loan closed to new applicants in 2025. Check the rebate calculator for current provincial and utility programs. Aeroseal specifically is covered by some utility rebate programs in Ontario and BC.
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