Do I need to retest for radon?

This tool takes your last radon result, when the test ran and how long it ran, and what has changed in your home since. It then says whether Health Canada’s rules call for a new test. The rules cover renovations, energy retrofits, earthwork beside the house, a new mitigation system and a low result from a test outside the heating season. The tool cannot measure the radon in your home; only a test can do that. It makes no prediction about your health.

Retest after a renovation, an energy retrofit or earthwork beside the house

Health Canada recommends a new test in the next heating season after any of these changes. A result from before the change may no longer describe the home.

• A renovation that affects the structure or the ventilation
• An energy retrofit, such as new windows, insulation or sealing
• Significant excavation or earthwork next to the home
• New structural damage in areas in contact with the ground
• The basement or main floor becoming the lowest lived-in level

Read the questions people ask about retesting and renovations.

Retest once a mitigation system goes in, then keep testing it on a schedule

After a system goes in, the fan runs for at least 24 hours, then a test of at least 48 hours checks it. A long-term test follows in the next heating season, done by someone other than the installer. Retest a home with an active soil depressurization system every five years. Health Canada’s reduction guide puts the first long-term test within two years of the system starting up.

A consumer radon monitor has a separate five-year rule that applies to the device rather than the home. Health Canada says to consider replacing an electronic monitor five years after you buy it, unless it has been recalibrated to the manufacturer’s specifications. Many consumer monitors cannot be recalibrated.

See how the system works, what the gauge shows and the tests that follow.

A low result from a test outside the heating season needs a second test

A long-term test runs 91 days or more, with at least 91 of those days in the heating season. A result at or below 200 Bq/m³ from a test with fewer than 91 heating-season days may underestimate the annual average. Test again in the next heating season before you rely on it.

A test of 91 days or more that reads above 200 Bq/m³ needs no retest. It calls for corrective action within one year, sooner the higher the level.

Find out what your last result means and whether its test was long enough.

If you now live on a lower level than you tested, test that level

The lowest lived-in level is the lowest floor with a room someone uses for more than four hours a day. If a level lower than the one you tested has become lived in, that level is the one to test.

See how to run the test.

A new home needs a test in its first heating season and again once it has settled

In a newly built home, test in the first heating season after you move in. Then retest two years after the year of construction. The second test checks the home once it has settled. Keep both results. The tool uses the most recent one, together with any change since.

Read about radon in new builds.

How to work it out by hand

Work through Health Canada’s rules in this order and note every step that applies to your home.

1. If the last test ran fewer than 91 days, whatever the result, run a new long-term test in the next heating season. If it ran 91 days or more but had fewer than 91 heating-season days, and the result was at or below 200 Bq/m³, retest in the next heating season.
2. If the last test ran 91 days or more and the result was above 200 Bq/m³, act within one year. No retest comes first. If a mitigation system has gone in since that test, follow step 4 instead.
3. If anything on the trigger list above has happened since the last test, retest in the next heating season.
4. If a mitigation system has gone in, run the fan for at least 24 hours, then test for at least 48 hours. Run a long-term test in the next heating season, then retest every five years.
5. If the home is newly built, test in the first heating season after occupancy and again two years after the year of construction.
6. If a lower level than the one you tested has become lived in, test that level.
7. If your consumer monitor is five years old, that is a question about the device rather than a retest rule.

See how the Index checks its numbers and dates.