Air Leakage Calculator

How to Use the Air Leakage Calculator

Air Leakage in Canadian Homes: ACH50, ELA, and Heat Loss

Air leakage is responsible for 25-40% of heating energy consumption in most Canadian homes. It's driven by the combined effect of stack pressure (warm air rising and escaping through high openings while cold air enters low ones) and wind pressure (which forces air in on the windward side and out on the leeward side). In a cold January in Edmonton or Winnipeg, both effects are extreme, making airtightness more valuable in Canada than almost anywhere else in the world. The infiltration load calculator can translate a measured ACH50 result directly into the heating or cooling load it adds to a furnace or heat pump sizing calculation.

What Blower Door Testing Measures

A blower door test is the standard method for measuring building airtightness in Canada. A calibrated fan is temporarily installed in an exterior door or window opening. The fan depressurizes (or pressurizes) the building to a standard reference pressure of 50 Pascals. The airflow rate required to maintain that pressure difference is the CFM50 value. Dividing by building volume gives ACH50.

The 50 Pa test pressure is about 10-20 times higher than the natural pressure difference driving infiltration in a typical home. That's why the N-factor division is needed to get from the test result to real-world infiltration. The advantage of the higher test pressure is that it amplifies small leaks enough to be measurable and locatable with smoke pencils or IR cameras, even on a calm day. A certified tester follows the same fan depressurization method covered in the blower door calculator lab, which walks through the raw pressure and flow readings behind an ACH50 result.

Canadian Airtightness Standards

The National Building Code of Canada (NBC 2020) requires new residential buildings to achieve 3.0 ACH50 or better, tested with a blower door before occupancy. Many provincial codes have adopted this requirement. BC Energy Step Code Step 2 and 3 tighten the target further. NRCan's R-2000 standard (a voluntary high-performance benchmark) requires 1.5 ACH50. Passive House certification (PHI or PHIUS) requires 0.6 ACH50 or better.

For comparison, the Canadian average existing housing stock sits around 5-7 ACH50. Pre-1980 homes often measure 8-12 ACH50. A well-sealed renovation can typically achieve 2.5-4.0 ACH50 without major structural changes.

Equivalent Leakage Area (ELA)

ELA translates an abstract ACH50 number into something more physically intuitive: the total area of all cracks, gaps, and penetrations in the building envelope, expressed as a single equivalent hole. The ELA calculation uses the ACH50 value, the building volume, and an assumed flow coefficient to determine the equivalent orifice size at a reference pressure of 4 Pa (closer to real-world conditions than 50 Pa). A 200 m2 home at 5.0 ACH50 might have an ELA of 500-700 cm2, comparable to leaving a small window open year-round. Reducing that to 2.5 ACH50 would cut ELA in half, roughly equivalent to sealing a 20x15 cm hole in the wall.

Where Air Leaks in Canadian Homes

Studies by NRCan and the Canada Mortgage and Housing Corporation (CMHC) have mapped the typical distribution of air leakage in Canadian housing. The ceiling/attic interface (pot lights, attic hatches, top plates) accounts for roughly 30-40% of total leakage. Walls contribute 15-25%, especially around electrical boxes, windows, and rim joists. Floors and basements add another 15-20%. Plumbing and mechanical penetrations round out the rest. This is why air sealing at the attic floor and rim joist during a renovation often gives the biggest return on investment.

For full air sealing upgrade savings, use the air sealing savings calculator. To see the impact on overall energy use, run the annual energy cost calculator before and after your target ACH50.

Air Leakage vs. Ventilation

A common concern is that a tighter house becomes unhealthy. This is a real issue if mechanical ventilation is absent, but it's not a reason to accept unnecessary leakage. The solution is to build tight and ventilate right, the principle behind all modern Canadian energy codes. NBC 2020 requires mechanical ventilation (HRV or ERV) in new homes precisely because they're being built tighter. An HRV recovers 70-85% of the heat from exhaust air, making controlled ventilation far more efficient than depending on random cracks for fresh air. Use the HRV payback calculator to see the financial case for heat recovery ventilation.