Passive 1.5
R-2000 3.0
NBC 2020 6.0
Typical 10+
Leaky
Unit Conversions
Canadian Airtightness Benchmarks
Full Analysis
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How to Use the Blower Door Calculator
Modern blower door instruments (Minneapolis Blower Door, Retrotec, and similar) display CFM50, ACH50, and L/s50 simultaneously. Choose whichever number you have from the test report. If you're working from an EnerGuide report, ACH50 appears prominently in the summary section.
Conditioned floor area and ceiling height determine building volume, needed to convert CFM50 to ACH50. This excludes unheated garages, unconditioned crawlspaces, and unfinished attic space above the insulation level, use conditioned volume only.
N converts ACH50 to natural infiltration under real-world conditions: N = 16-17 for Ontario/Quebec, 18-20 for Alberta/Saskatchewan (stronger wind and stack effect), 12-14 for coastal BC. Add your fuel type and rate for an annual heat loss cost estimate, or use the air leakage calculator for a fuller breakdown, or the infiltration calculator to size makeup ventilation for the natural ACH result.
Your result is checked against six Canadian benchmarks: NBC 2020 minimum (3.0 ACH50), NRCan R-2000 (1.5), BC Energy Step Code Step 3 (2.5) and Step 5 (0.6), Passive House PHI (0.6), and typical existing housing stock (5-7). Each card shows pass or fail against that standard.
Blower Door Testing in Canada: Standards, Methods, and What the Numbers Mean
Blower door testing is the primary method for measuring building airtightness in Canada and is required by NBC 2020 for new residential construction. Understanding how to read and interpret blower door results helps homeowners, builders, and energy auditors make better decisions about air sealing investments and compliance verification.
How the Blower Door Test Works
A blower door consists of a calibrated fan, a frame that mounts in an exterior door or window opening, pressure gauges, and software that controls the test protocol. The fan depressurizes or pressurizes the building to a series of test pressures, most commonly 50 Pascals. At each pressure point, the software records the airflow required to maintain that pressure. The 50 Pa test pressure is the industry standard because it's high enough to detect small leaks with smoke pencils or IR cameras, yet low enough to avoid damaging pressure-sensitive components like heat exchangers.
Some programs, including NRCan EnerGuide, require a full multi-point test (typically 10-12 pressure points from 25-60 Pa) to characterize the leakage curve and calculate the flow exponent n. This allows more precise extrapolation to natural pressure differences. Single-point tests at exactly 50 Pa are acceptable for pass/fail compliance verification under NBC 2020, and both options are defined in the Standards Council of Canada's CAN/CGSB-149.10 fan depressurization test method.
CFM50 vs ACH50: Which Number Matters
CFM50 is the raw measurement from the instrument: the actual cubic feet per minute of airflow through the fan at 50 Pascals. It's an absolute number that tells you the total leakage rate of the building regardless of its size. ACH50 normalizes CFM50 by building volume, expressing leakage as air changes per hour. ACH50 lets you compare buildings of different sizes on a common scale and is the metric used in Canadian codes.
The formula is ACH50 = (CFM50 × 60) / building volume in cubic feet. A 2,000 ft² bungalow with 9 ft ceilings has 18,000 ft³ of volume. At 1,500 CFM50, ACH50 = (1,500 × 60) / 18,000 = 5.0. The same 1,500 CFM50 in a 3,000 ft² two-storey home with the same ceiling height would give ACH50 = (1,500 × 60) / 27,000 = 3.3, a very different compliance picture.
L/s50: The Metric Alternative
Litres per second at 50 Pa (L/s50) is the metric equivalent of CFM50 used in some Canadian energy modelling tools, NRCan documentation, and Quebec-specific reporting formats. The conversion is straightforward: multiply CFM50 by 0.4719 to get L/s50. So 1,500 CFM50 equals 708 L/s50. NRCan's HOT2000 software accepts both units, and EnerGuide test reports typically show all three: CFM50, ACH50, and L/s50.
Canadian Airtightness Standards: A Full Comparison
Canada has multiple airtightness standards at different levels of stringency. NBC 2020 sets the baseline at 3.0 ACH50 for new residential construction, the minimum required for a new home to receive an occupancy permit in adopting jurisdictions. BC Energy Step Code (mandatory in BC) adds intermediate steps: Step 2 requires 3.0 ACH50, Step 3 requires 2.5 ACH50, Step 4 requires 1.5 ACH50, and Step 5 (near zero energy) requires 0.6 ACH50.
NRCan's voluntary R-2000 standard requires 1.5 ACH50. Passive House Institute (PHI) and PHIUS both require 0.6 ACH50. The Canadian Passive House Institute targets are identical for both pressurization and depressurization, averaged. The now-closed Canada Greener Homes Grant used the EnerGuide blower door result as one input to the energy model that determined eligible upgrades and rebate amounts; provincial and utility programs are the main source of airtightness-linked incentives now, and the airtightness calculator can check a result against a specific provincial code's requirement directly. For air sealing savings projections, use the air sealing savings calculator.
Frequently Asked Questions
A blower door test measures building envelope airtightness. A calibrated fan mounted in an exterior door depressurizes the home to 50 Pascals. The airflow required to hold that pressure is the CFM50 value. Dividing by building volume gives ACH50. The test is the mandatory method under NBC 2020 for verifying new home airtightness, and is required for NRCan EnerGuide ratings. It can also locate air leaks using smoke pencils, IR cameras, or acoustic detectors when the building is under pressure.
CFM50 is the raw airflow reading from the blower door fan, an absolute number in cubic feet per minute at 50 Pa. ACH50 divides CFM50 by the building volume in cubic feet (and multiplies by 60 to convert minutes to hours), normalizing for building size. Canadian codes use ACH50 because it allows fair comparison between homes of different sizes. The conversion is: ACH50 = (CFM50 × 60) ÷ building volume in ft³. This calculator does the conversion automatically when you enter floor area and ceiling height.
NBC 2020 requires 3.0 ACH50 or better for new residential construction, verified by a blower door test before occupancy. Most provinces are in the process of adopting NBC 2020 or an equivalent provincial code with the same requirement. Higher performance standards include NRCan R-2000 at 1.5 ACH50, BC Energy Step Code Step 3 at 2.5 ACH50, and Passive House at 0.6 ACH50. For existing homes, there's no mandatory retrofit airtightness requirement. The federal Canada Greener Homes Grant, which rewarded airtightness improvements measured by pre- and post-retrofit blower door tests, closed to new applicants in 2025; provincial and utility programs are now the main source of retrofit incentives.
Multiply CFM50 by 0.4719 to convert to litres per second at 50 Pa (L/s50). So 1,200 CFM50 equals 1,200 × 0.4719 = 566 L/s50. The reverse conversion is L/s50 × 2.119 = CFM50. L/s50 is used in some NRCan documentation, Quebec energy reporting, and HOT2000 input screens. This calculator accepts all three units as input and displays results in all three simultaneously.
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