Compliance Status by Standard
Calculated Values
Full Calculation Summary
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How to Use the Duct Leakage Compliance Calculator
Choose total duct leakage (measures all leaks, inside and outside conditioned space) or leakage to outside (only leaks escaping the conditioned envelope). Most modern codes reference leakage to outside as the more energy-relevant metric.
Ducts running through unconditioned attics, crawlspaces, or exterior walls face stricter thresholds in most programs than ducts installed entirely within conditioned living space.
Enter the measured CFM25 leakage from the test report and the system's rated airflow from the equipment nameplate. Floor area is optional and used only for the alternate per-100-sq-ft metric some codes reference.
The results show pass or fail status against Energy Star, Ontario SB-12, and IECC thresholds simultaneously, along with the leakage percentage calculated from your test data.
Understanding Duct Leakage Testing and Compliance
Duct leakage represents one of the largest and most preventable sources of HVAC energy waste in residential construction, which is why duct blaster testing has become a mandatory verification step in most current Canadian and US energy codes rather than a voluntary best practice. Understanding how the test works, what the results mean, and which threshold applies to a given project is essential for passing inspection and delivering genuinely efficient HVAC installations.
How the duct blaster test works
A duct blaster test uses a calibrated fan, typically connected through a register boot or a dedicated port sealed into the ductwork, to pressurize the duct system to a standardized test pressure of 25 pascals. The airflow the fan must supply to maintain this pressure directly indicates how much air is escaping through unsealed joints, damaged sections, or poor connections in the duct system. This CFM25 measurement is the raw test output, which is then converted to a percentage of the system's total rated airflow to produce the leakage percentage that compliance thresholds actually reference, since a fixed CFM leakage number means something very different for a small residential system than for a large commercial one.
Total leakage vs. leakage to outside
Total duct leakage measures every leak in the system regardless of where the leaked air ends up, including leaks between two rooms both within the conditioned envelope. Leakage to outside measures only the leaks that escape the conditioned space entirely, into an attic, crawlspace, garage, or exterior wall cavity. This distinction matters energetically: air leaking from one conditioned room to another conditioned room isn't truly lost, it's simply misdirected, while air leaking to an unconditioned space represents genuine wasted heating or cooling energy. Most current energy codes and certification programs, including Energy Star, use leakage to outside as the primary compliance metric for this reason, though total leakage testing remains common and is sometimes required as a supplementary check.
Why unconditioned duct runs face stricter requirements
When ductwork runs through unconditioned space, the energy consequences of any leak are more severe than when the same ductwork is entirely within conditioned living space. A leaking supply duct in an unconditioned attic loses heated or cooled air directly to the attic, wasting that energy entirely rather than simply delivering it slightly inefficiently within the home. A leaking return duct in the same location does the reverse: it actively pulls hot attic air into the system in summer or cold air in winter, adding an unwanted thermal load the equipment must then also condition. This is why compliance thresholds are generally stricter for ducts in unconditioned space, and why designers increasingly favour bringing ductwork entirely within the conditioned envelope, through techniques like conditioned attic assemblies or interior chase routing, specifically to sidestep this leakage energy penalty altogether.
Comparing thresholds across Canadian and US programs
Energy Star for New Homes, Ontario's SB-12 supplementary standard, and the International Energy Conservation Code each set duct leakage thresholds, and while they're broadly similar in magnitude, the exact percentage, the specific metric (total vs. to outside), and whether ducts-in-conditioned-space qualify for a relaxed threshold all vary by program and edition. A system that passes one program's threshold isn't automatically compliant with another, so confirming which specific standard applies to a given project, and checking the current edition's exact numerical threshold, is an essential first step before relying on a general industry rule of thumb. This calculator checks your test result against all three programs simultaneously so you can see where your result stands relative to each.
Sealing strategies to meet stricter thresholds
Mastic sealant applied to all visible duct joints and seams remains the gold standard for durable, long-lasting duct sealing, generally outperforming tape-based solutions over the long term since mastic doesn't dry out or lose adhesion the way many tapes eventually do. UL 181-rated foil tape is an acceptable alternative for many joint types when properly applied to clean, dry surfaces. For new construction specifically, using mastic-sealed duct board or fully-sealed metal ductwork systems designed with leakage prevention in mind from the outset typically achieves compliance more reliably and cost-effectively than attempting significant remediation on an already-installed system that failed its initial test. Use the HVAC commissioning checklist to build duct sealing verification into your standard project workflow rather than treating it as an afterthought before final inspection.
Frequently Asked Questions
A duct blaster test uses a calibrated fan connected to the ductwork through a register or dedicated test port to pressurize or depressurize the duct system to a standardized test pressure, typically 25 pascals. The fan airflow required to maintain that pressure indicates how much air is leaking from the duct system through unsealed joints, connections, and damaged sections. Duct leakage can be measured as total leakage (all leaks, both inside and outside the conditioned space) or leakage to outside (only leaks that escape the conditioned envelope entirely), with leakage to outside being the more energy-relevant measurement for most compliance programs. Enter your CFM25 result into this calculator for an instant compliance check.
Energy Star for New Homes typically requires total duct leakage of 4% or less of the system's rated airflow, or leakage to outside of 3% or less, though specific program versions and regional requirements can vary. This is measured using a duct blaster test at 25 pascals test pressure, with the leakage expressed as a percentage of the air handler's rated CFM. Ducts located entirely within the conditioned space face a somewhat less stringent test in some program versions, since leakage within conditioned space is less energetically wasteful than leakage to unconditioned attics, crawlspaces, or exterior walls. Select your duct location and test type in this calculator for the applicable threshold.
When ductwork runs through unconditioned spaces such as attics, crawlspaces, or exterior walls, any air leaking from a supply duct is conditioned air (heated or cooled at real cost) that escapes to unconditioned space and is entirely wasted rather than reaching the intended room. Leaking return ducts in unconditioned spaces have the opposite but equally problematic effect: they draw in hot attic air in summer or cold crawlspace air in winter, forcing the HVAC system to condition that unwanted air load in addition to the home's actual thermal load. This is why duct leakage to outside carries more weight in most compliance calculations than leakage confined entirely within conditioned space.
Research by building science organizations has found that ductwork with significant leakage running through unconditioned spaces can waste 20 to 30% of a home's heating and cooling energy, representing one of the largest single sources of HVAC system energy loss in typical residential construction. This substantial waste is why duct sealing has become a mandatory requirement rather than a voluntary best practice in most current Canadian and US energy codes, and why duct leakage testing has become a standard verification step for new construction and renovation projects seeking energy code compliance or certification. Use the energy code compliance calculator to see how duct performance fits into your broader code compliance path.
Related Compliance Tools
Full provincial supplementary standard
International Energy Conservation Code
Building envelope airtightness testing
Build sealing verification into workflow
Broader energy code cross-check
Ductwork permit requirements