A note before you read. This is general consumer information for Canadian homeowners, buyers, sellers, landlords, and renters, drawn from publicly available Health Canada and Canadian National Radon Proficiency Program (C-NRPP) sources. It is not medical, legal, or warranty advice. Radon results are reported against the Health Canada guideline of 200 Bq/m³; RadonTest.ca coordinates testing logistics and does not interpret individual results or provide health assessments. Decisions about mitigation should be based on a completed long-term test and, where the level is high, the advice of a C-NRPP-certified mitigation professional.
Key facts at a glance
- Active soil depressurization (ASD) — also called sub-slab depressurization — is the standard method and the one Health Canada calls the most effective and most common. In most homes it reduces radon by more than 80%.
- A system installs in about a day — Health Canada says "in less than a day" — for roughly the cost of other common home repairs.
- The fan runs continuously. It is never switched off; that's how the system keeps soil gas out of your living space.
- A typical system costs about $2,000–$3,000 (Health Canada's estimate). Real-world installed-cost data puts the average a little under that, with complex homes costing more.
- Use a C-NRPP-certified mitigation professional. Health Canada recommends it, and the directory is at c-nrpp.ca/find-a-professional.
- Ventilation and HRVs give only modest reductions. Health Canada says the effectiveness of ventilation for radon is limited; an HRV might lower radon by about 25–50% in most homes. For a large reduction, active soil depressurization is the recommended fix — not ventilation.
- Air purifiers do not remove radon gas. Filtering the air does nothing to the gas itself; you have to keep it out of the home or vent it.
First, test — then fix
Mitigation is the second step, never the first. Health Canada recommends taking action to reduce radon if your long-term result is at or above 200 Bq/m³ — and acting within one year, sooner the higher the level. A result of, say, 700 Bq/m³ warrants moving quickly; one of 230 Bq/m³ still needs fixing, but you have a little more breathing room to plan it well.
A few points worth keeping straight before you call a contractor:
- The decision to mitigate should rest on a long-term test of at least 91 days (three months), ideally over the heating season — not a short-term snapshot. Short-term tests are only appropriate for checking a system after it's installed.
- A high result is a solvable problem with a well-established fix. If your number came back above the guideline, start with our walkthrough of what to do if your radon level is above 200 Bq/m³.
- There's no need to panic over timing. Radon exposure is a long-term risk, not an acute one. The goal is to get the level down to as low as practical, properly, within the year.
Active soil depressurization (the standard method)
When people picture "radon mitigation," this is almost always what they mean. Active soil depressurization (ASD) — its sub-slab form is called sub-slab depressurization — is, in Health Canada's words, "the most effective and reliable radon reduction technique" and "the most common method used by C-NRPP certified professionals."
How it works. A pipe is installed through the foundation floor slab into the crushed rock or soil beneath the home. A fan attached to that pipe runs continuously, drawing the radon-laden soil gas out from under the house and venting it outdoors, where it dilutes harmlessly. Just as importantly, the system reverses the air-pressure difference between the house and the soil. For most of the year the air inside a home is at slightly lower pressure than the soil around the foundation, which actively draws soil gas (and radon) in through cracks and openings; ASD flips that, so the home stops pulling radon up from the ground. In most homes this reduces radon by more than 80%. Sometimes a single suction point does the job; larger or more complex homes may need more than one.
How long it takes. A system can usually be installed in less than a day, for about the same cost as other common home repairs.
Where it vents, and where the fan goes. The pipe can be vented either at roof level or at ground level. The fan must sit outside the living space of the home — commonly in the basement, a garage, or an attic. If it's mounted inside the living space, it's typically vented sideways through the rim joist near ground level, with the fan close to the discharge. If it's in an attic or garage, it usually runs up above the roofline. Wherever it goes, the pipe and joints must be tightly sealed so the system pulls proper suction and doesn't leak radon back indoors.
The cold-climate caveat. This matters in Canada specifically. A fan and pipe located in an unheated space — an attic or garage — will get cold in winter, and that can cause condensation and even ice build-up, which can damage the fan and reduce the system's effectiveness. Health Canada notes that this can be avoided by placing the fan indoors with a short ground-level discharge (much like the power-vented exhaust on a gas water heater), keeping almost the whole system in conditioned space. A good C-NRPP installer will weigh this for your climate and house layout. (For confirming the system actually works once it's running, see is my radon mitigation system working?)
Other system types
ASD is one idea — pull soil gas out from under the home — applied to different foundations. Your contractor's diagnostic tests determine which variant fits.
- Sub-membrane depressurization (for crawl spaces). A crawl space usually has exposed soil, so there's no slab to suck through. The fix is to lay a thick, sealed polyethylene membrane over the soil, seal it to the foundation walls, and run a fanned pipe through it to draw radon from underneath the plastic and vent it outside. Careful sealing around the pipe penetration is what makes it work. (Crawl spaces and unfinished basements both come up in our guide to radon in basements.)
- Drainage-system (drain-tile) depressurization. Many homes have drain tiles or perforated pipe ringing the foundation to carry water away. Applying suction to that loop can effectively reduce radon — Health Canada notes it works especially well for block-wall foundations — but only if the tile forms a complete loop around the foundation. If it covers just part of the perimeter, it's less effective.
- Sump-hole depressurization. If a basement has a sump pit, the pit can be capped and sealed so it keeps draining water while doubling as the suction point for the radon pipe. (If a floor drain feeds the sump, a trap is added so house air isn't pulled in through the drain.)
A note on terminology. You may see "block-wall depressurization" online — that's a U.S. term for sucking radon directly from the hollow cores of a concrete-block foundation wall. Health Canada does not frame it that way. In Canada, block-wall foundations are handled through drainage-system depressurization combined with sealing the voids at the tops of block walls. If a contractor quotes you "block-wall suction," ask them to explain the approach in Health Canada's terms.
Sealing cracks and openings
Sealing the obvious entry routes — the floor/wall joint, gaps around utility penetrations, open sumps, floor drains, voids at the top of block walls, and visible cracks — is a sensible part of almost any mitigation job. Health Canada describes sealing as "a basic part of most approaches to radon reduction" that can increase a system's effectiveness.
But here's the important limit: sealing on its own is not a standalone fix. It is too difficult to find, reach, and permanently seal every opening where soil gas gets in, and as a house settles, seals deteriorate and new cracks appear. So treat sealing as something that makes an active system work better — not as a substitute for one. The cost of sealing varies widely, from a few hundred dollars to $2,000 or more, mostly because a thorough job is labour-intensive.
Does ventilation or an HRV reduce radon?
This is the question that trips homeowners up most, so let's be precise about what Health Canada actually says.
A heat recovery ventilator (HRV) — or energy recovery ventilator (ERV) — increases ventilation by bringing in outdoor air while using the outgoing stale air to temper it, so you don't lose all your heat. More fresh air does dilute indoor radon somewhat. In most homes, an HRV might reduce radon by about 25 to 50%.
That sounds useful, and in the right situation it is — but note the ceiling. Health Canada is explicit that the effectiveness of ventilation for radon reduction is limited and only appropriate where modest reductions are needed. Two conditions shape whether it helps at all:
- It works best in airtight homes with low natural ventilation (homes that aren't already "drafty"). In a leaky house, adding an HRV does relatively little.
- It must be properly balanced — equal intake and exhaust airflow. An unbalanced system can depressurize the house, which draws in more radon, exactly the opposite of what you want. HRVs used for radon need to run continuously, stay balanced, and have their filters maintained.
The bottom line, in Health Canada's framing: when large reductions (50% or more) are needed, active soil depressurization is almost always the recommended approach. An HRV is a reasonable tool only when your level is modestly above the guideline and the home is a good candidate — and even then, many homeowners and contractors go straight to ASD because it's more effective and more reliable. An HRV does not "solve" or "get rid of" radon; think of it as a partial, conditional measure.
What about air purifiers? Plainly: air purifiers and filters do not remove radon gas. Radon is a gas, not a particle, so HEPA filters and ionizers don't capture it — this is a point made by the U.S. Environmental Protection Agency and follows from basic physics. (Filters can capture some of radon's solid decay products floating in the air, but that does not address the gas or the underlying risk.) Health Canada's guidance doesn't address purifiers because they aren't a mitigation method. If a product promises to "filter out radon," be skeptical.
New homes: passive rough-in vs active system
If your home is newer, it may already have part of a mitigation system built in. Under the National Building Code (and the provincial codes that adopt it), many new homes include a radon rough-in: a sealed soil-gas membrane under the slab plus a capped vertical pipe running up through the house, ready for a fan.
The key distinction:
- A rough-in or passive stack is just that — passive. The capped pipe relies on natural air movement and provides only limited, unverified protection on its own.
- It becomes an active system the moment a fan is added to make it draw soil gas continuously — exactly like the ASD systems above.
So a new home with a rough-in isn't automatically protected. You still test it like any other home, and if the long-term result is at or above 200 Bq/m³, a certified pro activates the rough-in by adding (and properly venting) a fan — usually a faster, tidier job than retrofitting from scratch. For how the codes handle this across the country, see Canadian building codes and radon and our guide to radon in new-construction homes.
What it costs — and what the fan costs to run
Two reliable cost references, plus the ongoing running cost:
Up-front installation. Health Canada estimates a typical sub-slab or sub-membrane system costs about $2,000–$3,000, including materials and labour. Industry data compiled by Take Action on Radon from systems installed across Canada (2013–2021) puts the average around $2,700, with most jobs in the low thousands. Costs vary widely by home, though — Take Action on Radon cites a range up to roughly $11,000 for complex installations (difficult foundations, multiple suction points, awkward access). An HRV, if that's the chosen route, runs about $1,500–$3,500 installed.
Running the fan. The fan runs continuously, and that costs only about $50–$75 a year in electricity, depending on fan size and local rates. The fan itself lasts five to ten or more years; when it eventually wears out, replacement runs about $200–$300. Budget for that one future swap and the modest annual electricity, and you have the lifetime cost of the system.
For a fuller breakdown by region and system type, see how much radon mitigation costs in Canada.
Who should do it — and confirming it works
Who. Health Canada recommends hiring a contractor certified as a radon mitigation professional under the Canadian National Radon Proficiency Program (C-NRPP). Lowering radon properly takes specific diagnostic skill — sizing the fan, finding suction points, sealing correctly, and avoiding new problems. Search the directory at c-nrpp.ca/find-a-professional, get more than one written estimate, and ask for proof of certification and references. RadonTest.ca does not perform mitigation or recommend specific companies — our guide on how to choose a radon mitigator walks through the questions to ask.
The safety check. Any active depressurization system can, if poorly set up, depressurize a room enough to cause back-drafting — where combustion gases from a furnace, water heater, fireplace, or wood stove spill back into the home instead of venting outdoors. A combustion-safety / back-draft check is a necessary part of the job, done by a trained radon specialist or heating contractor.
Confirming it actually worked. A drop on the manometer isn't proof of a risk-free annual average. Health Canada's two-step verification:
- A short-term test at activation (started at least 24 hours after the fan is on), ideally in the original test location, to show the system is working.
- A long-term test the following heating season to confirm the annual average is now below the guideline.
Crucially, to avoid a conflict of interest, that confirmation test should not be done by the company that installed the system. After that, plan to re-check the system with a long-term test within two years of activation and at five-year intervals afterward. See is my radon mitigation system working? for how to verify and maintain it.
Frequently asked questions
How does radon mitigation work? The standard method, active soil depressurization, runs a pipe through the foundation slab (or under a sealed crawl-space membrane) with a continuously running fan that draws radon-laden soil gas out from under the home and vents it outside before it can enter your living space. This also reverses the pressure difference that pulls radon indoors.
How much does mitigation reduce radon? In most homes, active soil depressurization reduces radon by more than 80%, according to Health Canada. The exact reduction depends on your home, the radon level, and how thoroughly the job is done.
Does an HRV or extra ventilation get rid of radon? No — it doesn't "get rid of" radon. An HRV might reduce levels by about 25–50% in most homes, and Health Canada says ventilation's effectiveness is limited and suited only to modest reductions. It works best in airtight homes and must be balanced so it doesn't depressurize the house and pull in more radon. For a large reduction, active soil depressurization is the recommended fix.
Do air purifiers remove radon? No. Radon is a gas, and air purifiers and filters do not remove it — a point made by the U.S. EPA and grounded in basic physics. Filtering air doesn't address the gas or the underlying risk; you need to keep radon out or vent it from beneath the home.
How much does radon mitigation cost? Health Canada estimates about $2,000–$3,000 for a typical system. Take Action on Radon's installed-cost data put the average around $2,700, with complex homes costing more (up to roughly $11,000). Running the fan adds about $50–$75 a year.
Can I install a radon system myself? Health Canada recommends a C-NRPP-certified mitigation professional, because proper diagnostics, fan sizing, sealing, and a combustion-safety check are needed to do it correctly and safely. If you're weighing the trade-offs, read our DIY radon mitigation guide first — then consider a certified pro for the actual install and verification.
How long does a system last, and what about the fan? A well-built ASD system is long-lived. The fan typically lasts five to ten or more years, and replacement costs about $200–$300. The fan must run continuously and is never switched off. Re-test with a long-term test within two years of activation and every five years afterward.
Does a new home with a radon rough-in still need anything? Possibly. A rough-in is a passive capped pipe — it's not an active system until a fan is added. Test the home like any other; if the long-term result is at or above 200 Bq/m³, a certified pro activates the rough-in by adding and venting a fan.
Test first — then fix with confidence
You can't mitigate what you haven't measured, and the right system depends on your actual number and your home. Start with a long-term test; if it comes back at or above the guideline, a C-NRPP-certified professional can usually fix it in about a day.
Order your RadonTest.ca kit → — lab analysis by a C-NRPP-certified laboratory (with an all-in-Canada analysis option), tracked shipping both ways, and your result delivered with clear Health Canada context.
Sources
- Health Canada — Reducing radon levels in your home (sub-slab depressurization; ">80%" reduction; installs in less than a day; ventilation/sealing effectiveness limited; C-NRPP), modified 2025-10-09. https://radontest.ca/links/hc-mitigation-guide
- Health Canada — Radon: Reduction Guide for Canadians (ASD mechanism and venting; sub-membrane, sump-hole and drainage-system depressurization; block-wall handling; sealing not standalone; HRV 25–50% and balanced airflow; costs $2,000–$3,000, fan $50–$75/yr, fan lifespan 5–10+ yrs, replacement $200–$300; back-draft check; follow-up testing; new-home rough-in/passive stack/active levels), published Feb 2023, modified 2025-09-24. https://www.canada.ca/en/health-canada/services/environmental-workplace-health/reports-publications/radiation/radon-reduction-guide-canadians-health-canada.html
- Take Action on Radon — Reducing radon (installed-cost data, ~$2,700 average and range to ~$11,000; ASD explainer; C-NRPP governance). https://takeactiononradon.ca/protect/reducing-radon/
- C-NRPP — Find a Professional (directory of certified measurement and mitigation professionals). https://c-nrpp.ca/find-a-professional/
Air-purifier note attributed to the U.S. Environmental Protection Agency and the physics of gas filtration, not to Health Canada (which does not address air purifiers as a mitigation method). Lab analysis is performed independently by a C-NRPP-certified laboratory; results are reported against the Health Canada guideline of 200 Bq/m³. RadonTest.ca coordinates kit logistics and sample submission only — it does not interpret or modify lab results and does not provide medical, legal, or warranty advice. Information attributed to Health Canada, Take Action on Radon, and others is summarized from the public sources listed above; confirm time-sensitive details (program availability, code requirements) with the responsible body.