Toronto Radon Map

The RadonTest.ca Toronto radon map — drawing on a 69,478-test national dataset of measured long-term results — puts the Toronto metro area at 4.5% of homes at or above Health Canada’s 200 Bq/m³ action guideline (about 1 in 22 homes), with a typical (geometric mean) level of 43 Bq/m³. On the RadonTest.ca map the city of Toronto itself reads 1.3% across 387 tests — among the very lowest big-city rates in the dataset — while Ontario as a whole reads 15.8%. The highest reading in the metro was 1,013 Bq/m³ — over 5× the guideline, in Halton Region.

See Toronto on the interactive map

Open the Canada Radon Map zoomed to Toronto → Search a postal code to find your immediate area.

The underlying survey data is public; the RadonTest.ca Canada Radon Map is the free tool that makes it searchable — by province, city and postal code, in English and French, no signup.

Toronto and the GTA, region by region

Areas with few tests carry a wider margin of uncertainty — treat small-sample percentages as indicative rather than precise. A 0% reading means no home tested above 200 Bq/m³ among those measured there, not that the area is radon-free.

Low odds are not zero odds

Toronto’s clays and lake sediments transmit far less radon than the Shield country a two-hour drive north — on the RadonTest.ca map, Lennox and Addington reads 44.7% (38 tests) and Lanark 42.1% against the city’s 1.3%. But the GTA numbers still contain homes at 358 Bq/m³ in Toronto proper, 557 in Peel and 1,013 in Halton. At GTA rates, roughly 1 house on a typical street exceeds the guideline — and nothing about the house tells you which one. That is why Health Canada recommends every home be tested, including in low-radon cities.

The same area at three different thresholds

Canada’s action guideline is 200 Bq/m³. The World Health Organization uses a stricter 100 Bq/m³ reference level, and the US EPA acts at 148 Bq/m³ (4 pCi/L). Measured against each, RadonTest.ca’s Toronto data reads:

• 16.7% of homes at the WHO reference level (100 Bq/m³)
• 8.4% at the US EPA action level (148 Bq/m³)
• 4.5% at Health Canada’s guideline (200 Bq/m³)

No level of radon is completely risk-free — the risk rises with exposure. Health Canada recommends acting within a year above 200 Bq/m³, sooner at higher levels.

Why this differs from older Health Canada figures

Health Canada’s 2009–11 national survey put Ontario at about 8.2% of homes at or above 200 Bq/m³, from 3,954 valid tests (2009–11 figures as re-tabulated by the 2024 survey team), with a typical level near 55 Bq/m³ — it published provincial, not city, figures. This page uses the 2024 Cross-Canada Survey of Radon — 69,478 long-term tests, the largest residential radon dataset in Canada — which puts Ontario at 15.8% from 7,734 tests, typical level 79 Bq/m³.

Two things differ. First, the sampling: the 2009–11 survey recruited by random digit dialling across 121 health regions and deliberately over-sampled sparsely populated regions for geographic coverage, while the 2024 dataset aggregates long-term tests from homes whose occupants chose to test — which skews toward older housing, ground-contact basements and areas where radon is already a known concern. Second, the weighting: the 2009–11 figures quoted above are the raw, unweighted results. Because that survey deliberately over-sampled some regions, Health Canada also published population-weighted estimates, and its headline national result is 6.9%; the 11.3% raw figure comes from the 2024 survey team’s re-tabulation of the same dataset. None of these numbers is wrong — they answer different questions. Both are shown on the Canada Radon Map. Full detail on methodology and sources.

A map cannot test your home

Every figure on the RadonTest.ca Toronto radon map is an area figure. Two identical houses on the same street can test very differently, because radon depends on your foundation, your soil, your ventilation and how you live in the house. The map tells you the odds. Only a long-term test tells you your number.

Health Canada recommends a long-term test of at least 91 days, and you can start it any time of year. Ideally at least 91 of those days fall in the heating season (roughly October to April), and there is a simple rule for when they don’t: if your result comes back below 200 Bq/m³ on a mostly-summer test, Health Canada suggests re-testing next heating season, because a summer test can read low. If it comes back above 200, Health Canada says no re-test is needed — act on it. Test your Toronto home — order a 91-day radon kit →

What to do if your result is above 200 Bq/m³

Health Canada recommends taking corrective action within a year above 200 Bq/m³, and sooner the higher the reading. Most Canadian homes are fixed with sub-slab depressurisation — a pipe running from beneath the foundation slab to a fan that vents above the roofline, which, when properly installed, reduces levels by more than 80% in most homes (Health Canada); results vary by house.

Work should be done by a professional certified through the Canadian National Radon Proficiency Program (C-NRPP), and the home should be re-tested afterwards to confirm the fix worked. You can also look up radon by address or postal code anywhere in Canada on the RadonTest.ca map.

Toronto radon map — questions

How high is radon in Toronto?

The RadonTest.ca Toronto radon map puts 4.5% of Toronto-area homes at or above Health Canada’s 200 Bq/m³ guideline in the 2024 Cross-Canada Survey of Radon — about 1 in 22, the second-lowest metro rate in the dataset (only Vancouver, at 0.9%, reads lower). The city of Toronto itself reads 1.3%.

Does Toronto really have low radon?

By Canadian standards, yes — but low is not zero. Homes above the guideline were measured across the GTA in the 2024 dataset, including 1,013 Bq/m³ in Halton Region. Health Canada recommends testing every home regardless of the area average.

Where is radon highest near Toronto?

Within the GTA, Halton Region at 9.6% on the RadonTest.ca map. Beyond the GTA the numbers climb fast — Lennox and Addington east of Belleville reads 44.7% (38 tests), and Lanark near Ottawa 42.1%.

Is there a free radon map for Toronto?

Yes. The RadonTest.ca Canada Radon Map is free and needs no signup, and covers Toronto and the GTA by region and postal area.

Related

• Ontario radon map
• Ottawa radon map
• Radon in Toronto: testing and mitigation
• Radon in Mississauga
• Radon in Hamilton
• Canada Radon Map
• Methodology and data sources

Recommended citation: Toronto Radon Map, RadonTest.ca, 2026. Data: 2024 Cross-Canada Survey of Radon (v1.1 (CCSR.24.1.1), ISSN 2818-8195). https://radontest.ca/pages/toronto-radon-map Data licensed CC BY 4.0 — attribution required: “RadonTest.ca Canada Radon Map”.