Current Radon Level vs. Health Canada Guideline
Suction Point Coverage & System Sizing
Full Results Table
| Parameter | Value | Notes |
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How to Use This Calculator
Use the long-term average from a radon test of 91 days or more. Set your target reduction level, commonly 100 Bq/m³ or lower, well under the 200 Bq/m³ Health Canada guideline.
Soil and sub-slab aggregate permeability is the single biggest factor in system design. Gravel and coarse aggregate allow one suction point to cover a large area at low fan pressure. Clay requires higher pressure and often multiple suction points.
Total slab area, foundation type, and whether a sump pit is present all affect system design. A sump pit is often the easiest and most effective suction point location when present, since it already provides an opening to the sub-slab area.
The results show planning values for coverage area per suction point, the number of suction points needed for your slab area, and fan airflow and pressure. Actual fan selection should be verified with pressure field extension testing.
Radon Mitigation in Canadian Homes: System Design Fundamentals
Radon is a naturally occurring radioactive gas produced by the decay of uranium in soil and rock, present to some degree beneath virtually every home in Canada. It seeps into buildings through foundation cracks, sump pits, and other openings, and because it's odourless and invisible, testing is the only way to know if levels are high. Health Canada links radon exposure to about 16% of lung cancer deaths in Canada, roughly 3,200 deaths a year, making it second only to smoking as a cause of lung cancer.
How Sub-Slab Depressurization Works
The most effective and common radon mitigation approach is active sub-slab depressurization (ASD). Health Canada's Radon: Reduction Guide for Canadians names active soil depressurization as the most common reduction method and says levels in most homes can be reduced by more than 80%. A pipe penetrates the foundation slab into the soil or aggregate beneath, connected to a continuously running inline fan that exhausts above the roofline or out a gable end or sidewall. This creates negative pressure in the sub-slab region relative to the house, reversing the natural pressure gradient that draws radon-laden soil gas indoors. Instead, air is drawn from the house into the soil at a low rate, and radon gas is vented directly outside before it can enter the living space. The system doesn't remove radon from the soil; it prevents the soil gas pathway into the building.
Soil Permeability and System Design
The permeability of the material beneath the slab determines how far the negative pressure field extends from a single suction point, and therefore how many suction points a system needs. Under a slab with a layer of clean coarse gravel or crushed stone, a single suction point can cover a large area. With native soil, sand, or fill directly beneath the slab, coverage drops significantly, and in dense clay it can be small. This calculator uses planning values of 700 m² per suction point for gravel, 350 m² for sand or mixed fill, 150 m² for clay or silt, and 80 m² for dense clay. These are estimates, not measurements, which is why radon mitigators perform pressure field extension (PFE) testing after installing a temporary suction point, drilling small monitoring holes at increasing distances to measure at what point the negative pressure becomes too weak to be effective.
Fan Selection and Static Pressure
Radon fans are specified by two performance curves: airflow at zero static pressure, and static pressure at zero airflow (the fan's maximum "stall" pressure). Systems in permeable soil need fans that can move higher airflow at relatively low pressure. Systems in tight clay soil need fans that can generate high static pressure even at low airflow, since the resistance to air movement through the dense soil is the limiting factor. This calculator's planning values run from 125 Pa and 60 L/s for gravel to 750 Pa and 20 L/s for dense clay. Undersized fans in tight soil conditions fail to achieve adequate pressure field extension, leaving portions of the slab unprotected even though the system appears to be running. This is a common cause of radon mitigation systems that don't achieve the expected reduction. The fan laws calculator shows how a fan's airflow and pressure change with speed when a listed fan curve doesn't quite match the design point.
Multiple Suction Points and Complex Foundations
Larger homes, homes with multiple foundation types (a basement combined with an attached garage slab, for example), or homes with interior footings that create isolated sub-slab zones often require multiple suction points connected to a single fan through a manifold, or in some cases multiple independent fan systems. Each isolated sub-slab area needs its own pressure field coverage, because a suction point in the main basement typically cannot achieve adequate depressurization under a separate slab section isolated by an interior footing or foundation wall extending to the aggregate layer. Pipe runs from several suction points add friction that the fan has to overcome, and the friction loss calculator estimates that resistance for a given run.
National Building Code Rough-In Requirements
The National Building Code of Canada introduced radon provisions for new low-rise housing in its 2010 edition. The requirement is a rough-in for a future subfloor depressurization system, a pipe stub through the slab into the gravel layer that can be activated with a fan after the home is finished, along with sealing of the foundation membrane so it also acts as a soil gas barrier. Provinces adopt and extend this differently, and British Columbia's code, for example, now requires a radon vent pipe that runs through the building and terminates outside. A rough-in dramatically reduces the cost and disruption of adding active mitigation later compared to a full retrofit that requires slab penetration after the home is finished and occupied. It does not mean a new home has active mitigation from the start, so homeowners in new construction should verify the rough-in location and test for radon in the first year of occupancy to determine if fan activation is needed.
Testing and the Canadian Guideline
Health Canada's Guide for radon measurements in homes sets out the testing rules behind the numbers this calculator uses. The Canadian guideline is 200 Bq/m³ as an average annual concentration in the normal occupancy area. Tests should run 91 days or more, and the guide recommends mitigating within 1 year when the level is above 200 Bq/m³ and acting sooner when it is higher, reducing the level as low as reasonably achievable. It also notes that no level is considered risk free below the guideline. Health Canada's older guidance gave a 2-year window for levels between 200 and 600 Bq/m³, so older references may still show it. Mitigation should be designed and installed by a C-NRPP certified professional, and retesting after installation confirms the system achieved the expected reduction.
Frequently Asked Questions
The Canadian radon guideline is 200 becquerels per cubic metre as the average annual concentration in the normal occupancy area of a home. Health Canada's current guide recommends taking action within one year when a long-term test (91 days or more) shows a level above 200 Bq/m3, and acting sooner when the level is higher, reducing radon as low as reasonably achievable. No level is considered risk free below the guideline, so lower is always better. Older references gave a two-year window for levels between 200 and 600 Bq/m3 and one year above 600.
Sub-slab depressurization creates negative pressure beneath the foundation relative to indoor air. A pipe through the slab connects to an inline fan that continuously extracts soil gas and vents it above the roofline. This prevents radon-laden soil gas from entering through slab cracks and penetrations, since air now flows into the soil from the house rather than the reverse. Pressure field extension testing verifies the negative pressure reaches the entire slab area, not just near the extraction point.
Fan sizing depends on the airflow needed to maintain negative pressure across the slab and the static pressure the fan must overcome, which is determined largely by soil permeability. Highly permeable gravel needs higher airflow at lower pressure, while clay needs lower airflow but higher static pressure. This calculator uses planning values: about 700 m² of coverage per suction point for gravel, 350 m² for sand, 150 m² for clay, and 80 m² for dense clay, with fan pressures from 125 to 750 Pa. Those are estimates only, and pressure field extension testing on the actual slab decides how many suction points and what fan are needed.
The National Building Code of Canada has required a radon rough-in for new low-rise housing since its 2010 edition: a pipe stub through the slab into the gravel layer, ready for a fan to be added if testing later shows high radon. Provinces adopt and extend this differently, and British Columbia's code requires a vent pipe that terminates outside the building. The rough-in does not mean every new home has active mitigation from the start, and it makes adding a fan later straightforward and inexpensive. Existing homes built before the requirement, or without the rough-in, need a full retrofit including slab penetration if testing shows radon above the Health Canada guideline.
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