Where to Find a Reliable Radon Map for Ontario Homes

The most reliable radon map Ontario residents can use is the Canada radon map from Ecosense, which shows average residential radon concentrations by postal code. Health Canada sets the indoor action level at 200 Bq/m³, the threshold at which mitigation is recommended. That map gives you a regional starting point, not a diagnosis of your specific house.

Here’s what to do right now:

Go to the Canada radon map and enter the first three characters of your postal code (your FSA).
Compare your area’s average reading and percentage of homes above 200 Bq/m³ against the provincial picture.
Order or run a long-term test kit in your own home regardless of what the map shows, since only that result tells you what you’re actually breathing.

Key Takeaways

Ontario radon maps show regional probability using postal-code data, but only a long-term test confirms what a specific home is actually exposed to.

Point	Details
Start with the FSA lookup	Enter your postal code’s first three characters on the Canada radon map to see area averages and percent above guideline.
Know the action threshold	Health Canada sets 200 Bq/m³ as the level at which mitigation is recommended.
Test long, not short	Run a minimum three-month test, ideally through colder months, for an accurate year-round estimate.
Geology explains hot spots	Bedrock formations like the Billings Formation raise radon potential in parts of the Ottawa region regardless of what a neighboring FSA shows.
Get a certified measurement	Simon Air Quality’s Wave Radon Measurement detector and long-term test kits turn a map estimate into a confirmed reading for your address.

This article is general information, not a substitute for advice from a qualified doctor. Consult a qualified healthcare professional about your own circumstances before acting on anything here.

How to Read an Ontario Radon Map by Postal Code
Why Ontario Radon Levels Vary So Much From House to House
Ontario Radon Levels: What the Health Canada Numbers Actually Say
How to Test Your Home the Right Way
What to Do if Your Radon Test Comes Back at 200 Bq/m³ or Higher
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How to Read an Ontario Radon Map by Postal Code

The Canada radon map runs on FSA lookups, meaning you only need the first three characters of your postal code, like K1P or K2A, to pull up local data. Type that into the search field on the interactive map and it returns two numbers for that area: the average radon concentration in becquerels per cubic meter, and the percentage of tested homes that came in at or above Health Canada’s 200 Bq/m³ guideline.

Here’s how to actually use those numbers without misreading them:

Find your FSA first. It’s the section before the space in your postal code, covering a cluster of streets or a neighborhood, not just your address.
Check the average, not just the percentage. A low average with a high percent-above-guideline usually means a few homes are pulling way above normal, which matters if your house shares geology with them.
Look at neighboring FSAs too. Radon potential doesn’t respect postal boundaries, so a spike next door is worth noting even if your own FSA reads lower.

The map draws on Health Canada’s Cross-Canada Survey of Radon Concentrations in Homes, so coverage depends on how many homes in a given FSA were actually tested. Sparsely tested areas show wider uncertainty, and the underlying survey data isn’t refreshed on a fixed annual schedule, so treat every figure as a snapshot rather than a live reading.

Pro Tip: If your FSA shows no data or very few tested homes, don’t assume that means low risk. It often just means fewer people have tested there. Order a kit and become one of the data points.

Why Ontario Radon Levels Vary So Much From House to House

Radon maps model probability, not certainty. They combine soil chemistry, bedrock type, and past test results to estimate how likely homes in an area are to have elevated readings, but two houses on the same street can post wildly different numbers depending on foundation cracks, sump pits, and ventilation habits.

Geology drives most of that variation. In parts of the Ottawa region, bedrock like the Billings Formation and the Eastview member of the Lindsay Formation is associated with higher radon potential, which is why some pockets inside the same city run consistently hotter than their surroundings.

Maps indicate regional probability. They cannot predict a specific home’s radon level. Only a long-term test can confirm what’s actually inside your walls.

The most common misconception is treating a zone shown as lower radon potential as a free pass. Basements built directly over a crack in that same bedrock, or homes with a poorly sealed sump pump, can still test high regardless of the general area’s average.

A neighbor’s low reading tells you nothing definitive about your own home.
New construction, renovations, and foundation repairs can all change a home’s radon pathway over time.
The only way to know your number is to measure it yourself.

Ontario Radon Levels: What the Health Canada Numbers Actually Say

Health Canada’s guideline sits at 200 Bq/m³, the concentration at which the agency recommends taking action to reduce exposure. The Cross-Canada Survey that underpins the provincial averages found meaningful variation across regions, with some areas showing a notably higher share of tested homes above guideline than others.

Ontario as a whole isn’t uniformly high or low. Averages differ block by block, and certain pockets in the Ottawa region carry higher probability because of the bedrock formations mentioned earlier. That regional pattern is useful for context, but it’s a poor substitute for your own number.

The number that matters: 200 Bq/m³ is the line Health Canada draws between “acceptable” and “act on this.” Everything on a radon map exists to help you guess whether your home is near that line, not to tell you where it actually falls.

Provincial or municipal statistics describe a population of homes, not yours specifically. A high-probability FSA might contain plenty of houses that test well under guideline, and a low-probability one can still hide a single home with a direct soil-gas pathway into the basement.

How to Test Your Home the Right Way

Short-term test strips give you a rough read, but Health Canada recommends a long-term test of at least three months for an accurate picture, ideally run during colder months when doors and windows stay shut. Radon levels swing with the seasons and even with the weather, so a three-day snapshot in July can badly understate what you’re breathing in January.

Placement matters as much as duration:

Put the detector in the lowest lived-in level of the home, meaning a finished basement or a ground-floor room you actually use, not a crawlspace.
Keep it away from doors, windows, fireplaces, and heating vents, since drafts and airflow skew the reading.
Leave it undisturbed for the full test period and avoid running fans or opening windows more than usual.
Log the start and end dates so you can match the result to Health Canada’s action threshold accurately.

For sourcing a kit in Canada, Simon Air Quality’s long-term radon test kit is built for exactly this window, and TakeActionOnRadon’s Ontario page lists additional provincial suppliers and directories if you want to compare options. Avoid short-term kits marketed for real estate transactions if your goal is an accurate long-term average, since they answer a different question.

Skip testing during unusually windy or stormy weeks if you can help it, since pressure swings can distort short segments of a long-term test.
Test again after any major renovation, new foundation crack, or HVAC change, since those alter airflow patterns.

What to Do if Your Radon Test Comes Back at 200 Bq/m³ or Higher

A single high result doesn’t mean panic, but it does mean action. While you plan next steps, seal obvious cracks in the foundation and increase ventilation in the lowest level to reduce short-term exposure. These are stopgaps, not fixes.

The standard, most effective fix is sub-slab depressurization: a pipe and fan system installed under the foundation that draws radon gas from beneath the home and vents it safely outdoors before it enters living space. Other approaches, like sealing major entry points or adding a heat recovery ventilator, sometimes help at the margins but rarely bring a high reading down to guideline on their own. A technical overview of common mitigation methods walks through how these systems perform in practice.

Sub-slab depressurization is the go-to solution for the vast majority of elevated-radon homes.
Sealing cracks and sump lids helps but almost never solves a genuinely high reading by itself.
An HRV can improve overall air exchange but shouldn’t be your only response to a result at or above 200 Bq/m³.

Pro Tip: Ask any installer for their C-NRPP certification number before signing a contract. It’s the credential Health Canada points to for qualified radon professionals, and it takes thirty seconds to verify.

Hiring a certified professional matters here because a poorly designed system can actually depressurize the wrong zone or fail to reach the right soil layer. Look for someone who tests before and after installation, not just someone who installs and leaves. Simon Air Quality’s radon mitigation services follow that verify-then-install approach for Ontario homes.

A local perspective on maps, testing, and what actually gets missed

The map does its job well: it tells you where to be curious. What it can’t do is replace a proper measurement inside your own basement, and that gap is where we see homeowners make mistakes most often. We’ve measured plenty of Ottawa homes sitting in a lower-probability FSA that still came back well over 200 Bq/m³, usually because of a sump pit or a foundation joint the map has no way to see. Our Wave Radon Measurement detector exists for that exact blind spot: certified, long-term, and specific to your address, not your postal code. If a map result has you wondering, book a proper test before you assume anything either way.

— Mark

Testing kits, professional measurement, and mitigation for your specific home

A postal-code map is a starting point, not a verdict, and Simon Air Quality exists for the step after the map: turning a regional estimate into a real number from inside your house. Where a big national kit ships you a generic strip and disappears, our service pairs the test with local, certified interpretation and a mitigation plan if you need one, backed by follow-up rather than a one-time drop-off.

Our long-term radon test kit covers the full three-month window Health Canada recommends, and our Wave Radon Measurement detector gives you a certified, precise reading built for Ontario conditions rather than a generic average. If your result comes back elevated, our radon mitigation technicians handle everything from sub-slab depressurization design to post-installation retesting, so you get a documented result, not just an installed pipe. Start with a quick indoor air quality assessment to figure out exactly which service fits your home, and book your test before winter closes your windows for the season.

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Mark spent many years, time, and energy learning about various disciplines that he can now utilize together in the most effective way possible. Some of the credentials/certifications earned through Mark’s career include an HVAC license, IICRC, indoor air quality inspector from INTerNACHI, C-NRPP - radon measurement certification, radon mitigation certification.