Ontario Radon Map: Every Home Health Canada Tested, and What It Read

4,530 homes across Ontario were long-term tested for radon in the two federal surveys. Every one is a dot on this map, coloured by what it read, with the number of tested homes printed beside every district figure.

The Map

Every dot is one tested house. Zoom in for street names. Shaded districts had no home tested in either survey.

under 100100 to 147148 to 199200 and aboveno homes tested

4,530 measurements shown. Dot positions inside a district are illustrative, not addresses. The survey records which district a home was in, never where it stood. Tap any dot for its reading, or any district for its count and median. Rural districts here cover thousands of square kilometres, so a dot in one says very little about any particular corner of it.

Built from Health Canada's published measurements under the Open Government Licence. We do not sell radon testing or mitigation.

What the Numbers Say

10%

of tested Ontario homes at or above Canada's 200 Bq/m³ action level

median reading, Bq/m³

5,657

highest single reading, in P0T

Ontario sits 21st of the 33 places mapped with a hundred or more tested homes, at 10.4% at or above the action level, between Halifax at 35.2% and Toronto and the GTA at 2.2%. All on the same two surveys and the same method. The spread between places is real, and the spread between houses on one street is bigger still.

The Number Changes Depending on Whose Limit You Use

Canada acts at 200 Bq/m³. The United States EPA acts at about 148. The World Health Organization sets a reference level of 100. Applied to the same 4,530 homes:

10%

at or above Canada's 200

17%

at or above the US EPA's 148

32%

at or above the WHO's 100

Same houses, same measurements. Why the three numbers differ, and which one to use.

By Postal District, with the Sample Sizes Shown

Read the count column before the median column. A district resting on four houses is a hint, not a verdict, and those rows are greyed. The land area column matters too: a district covering ten thousand square kilometres is an average across a region, not a neighbourhood.

District	Land km²	Homes tested	Median	Highest	At or over 200
N1L	12	18	248	432	13
P7G	4,038	16	231	464	9
N8P	6	14	216	731	8
P8N	564	24	214	706	13
N8R	6	14	155	275	3
K7N	4	11	154	550	5
N8T	11	10	145	316	2
N3L	137	28	139	470	8
K7S	185	14	137	200	1
N4X	293	17	136	246	4
L9G	81	12	134	515	3
K7P	30	24	126	346	7
K9K	10	38	119	515	6
P7B	14	30	119	486	7
K7M	44	41	117	624	9
N8W	17	20	117	569	4
N9V	138	15	115	331	5
K0E	1,979	22	113	515	7
P3G	266	12	113	384	2
K7K	29	28	112	398	5
P3E	1,096	30	111	736	10
L0A	664	10	109	188	0
P7K	108	19	108	530	8
K7V	665	12	106	192	0
K4K	54	13	105	303	2
N8H	155	11	105	387	1
N9J	49	10	103	371	4
N9B	7	10	101	487	2
P3B	21	21	101	298	3
N7A	253	14	98	345	1
N9H	24	11	98	211	1
N0R	784	31	97	408	3
N8S	9	16	96	742	2
K0H	5,232	31	94	650	4
K7A	355	10	94	481	1
N9A	6	11	92	256	2
K0G	2,675	23	90	681	5
N8N	49	28	90	196	0
L0R	985	35	89	266	1
P7A	4,089	27	89	512	4
N0L	2,070	27	88	1246	3
P3A	47	32	88	324	1
N4S	295	26	87	749	5
P0T	94,592	54	87	5657	10
N1G	23	22	86	984	3
P3C	11	18	86	454	1
P5A	696	11	86	1023	2
N4W	271	10	85	625	2
N8A	359	24	85	497	5
N4K	356	12	84	487	3
N9E	15	15	83	450	4
L4M	78	40	82	757	4
N0P	2,849	90	82	891	20
P0W	14,647	33	82	500	3
K9H	17	52	81	231	4
N7M	326	46	81	634	11
P0J	8,531	56	81	873	6
N5Y	12	14	80	262	1
N0N	1,576	56	78	478	4
K0A	3,073	45	76	460	5
N0K	1,499	31	75	553	7
L9H	62	14	74	216	1
N7L	26	42	74	503	2
K9L	33	20	73	157	0
N5C	126	11	73	303	2
N7S	16	43	73	300	3
P0V	374,847	14	73	331	2
K7L	141	30	72	283	4
N2K	20	17	72	155	0
N3T	246	37	71	396	5

155 districts have ten or more tested homes, which is where these figures start to mean something. The table shows those; 316 districts with thinner samples are on the map but not listed here. 134 districts have no measurement at all and are shaded on the map.

What Actually Settles It

Nothing on this page describes your house. Radon varies enormously between homes on the same street, because it depends on how each building sits on and draws air from the ground beneath it. The highest reading here is 5,657 Bq/m³ and it sits in a district whose median is far below it. A long-term test in your own home is the only measurement that tells you anything about your home.

Also: every C-NRPP certified radon company here, the other city and province maps, and what radon actually is.

Sources and method. Radon measurements: Health Canada, Radon and Thoron Data From Canadian Homes (fifteen Ontario metros) pooled with the Cross-Canada Survey of Radon Concentrations in Homes 2009-2011, both under the Open Government Licence – Canada. Boundaries: Statistics Canada 2021 cartographic forward sortation area file, same licence. Percentages are calculated from the individual measurements shown, not quoted from a summary. Land areas are from the Statistics Canada boundary file.