Independent accuracy results for radon monitors, explained

C-NRPP's testing-process document (last revised 5 June 2025) describes the method. The work is done at the Radiation Safety Institute of Canada's National Radon Chamber in Saskatoon, a 12 cubic meter walk-in chamber that is certified as a secondary reference radon chamber under AARST's National Radon Proficiency Program (certificate SC 1005). The chamber's radon level is the yardstick each monitor's results are compared with.

1. 1Step 1 of 5:

   The maker enters

   Device manufacturers are invited to take part and send three of the same model. Entry is by registration, so a model is only tested if its maker signs it up.

2. 2Step 2 of 5:

   The units arrive sealed

   All monitors are shipped unopened to the chamber. Staff log the make, model and serial number, check for shipping damage, read the manual, install any app and confirm each unit works.

3. 3Step 3 of 5:

   Four rounds of exposure

   Each round lasts 7 days, in four different sets of conditions: two near Canada's guideline level (one at winter and one at summer temperature and humidity) and two at higher radon levels.

4. 4Step 4 of 5:

   A measurement error for each device

   C-NRPP compares each monitor's results with the chamber and calculates its Measurement Error, a single figure that combines precision and accuracy.

5. 5Step 5 of 5:

   A grade for each round

   Each monitor gets a letter grade, A to E, for each round. Those with an average grade of B or better are recommended.

C-NRPP sets two rounds at 200 Bq/m3 because that is the Canadian radon guideline level, about 5.4 pCi/L. The summer round uses conditions representing homes with no air conditioning or limited air conditioning, and the two higher rounds, at 400 and 1,000 Bq/m3, test how a monitor performs across a range of radon levels. EPA's action level in the United States is lower than Canada's guideline: EPA recommends fixing a home when the radon level is 4 pCi/L or higher.

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2 pCi/L

4 pCi/L

00 Bq/m³274 Bq/m³4148 Bq/m³6222 Bq/m³8296 Bq/m³10+370 Bq/m³

• Below 2 pCi/L (below 74 Bq/m³)Below both of EPA's guidance levels.
• 2 to 4 pCi/L (74 Bq/m³ to 148 Bq/m³)EPA recommends considering a fix when the level is between 2 and 4 pCi/L.
• At or above 4 pCi/L (148 Bq/m³ and up)EPA recommends fixing a home when the radon level is 4 pCi/L or higher.

C-NRPP grades each monitor in each round by its Measurement Error, a single percentage that reflects both how close the monitor's readings were to the chamber's level and how consistent they were. The bands come straight from C-NRPP's detailed results:

A manufacturer's accuracy figure and a C-NRPP grade are not the same measure. The maker's figure is a promise under conditions the maker chooses, such as ±10% after 7 days at 200 Bq/m3. The grade is C-NRPP's own result, under conditions C-NRPP sets. Read the maker's figure for the conditions it names, and the grade for what an independent test found.

C-NRPP's consumer monitor page lists six models as approved in the 2024/25 round, published May 2025. The table repeats what C-NRPP prints for each, including the manufacturer's stated accuracy, which is the maker's claim and not C-NRPP's finding.

The 2024/25 round was the second year of C-NRPP's project. Its 2023 report listed seven consumer monitors in its table of devices tested, marking these as passing its performance test: the Airthings Corentium Home, Wave Plus and View Plus, the Ecosense EcoQube, EcoBlue and RadonEye RD200, and the SunRadon Luft. It listed two devices it did not recommend, the Air Steward and the Radon Guard.

A model that appears in 2023 but not in 2024/25 was not retested in the later round; nothing in C-NRPP's 2024/25 material says it failed. We show the most recent result for each model and say which round it came from.

Many monitors sold in the United States have no C-NRPP result at all. There are three ordinary reasons, and none of them is a failed test:

• The maker did not enter it. C-NRPP's comparison is by registration: device manufacturers sign up for each annual round.
• It is new. A model released after a round closed cannot appear in that round's results.
• It is still under review. A device can be missing from both lists because it is still being tested, or is under review or regulatory action.

That is why every monitor on our hub carries one of three labels: approved in C-NRPP's 2024/25 evaluation, not included in C-NRPP's 2024/25 evaluation, or not approved. We never write "unverified" or "inaccurate" for a monitor that simply was not tested. Where a monitor has no independent result, we show the maker's own claims, attributed to the maker.

Chamber tests control the conditions. Field studies run monitors in real rooms beside a calibrated reference instrument, which shows how they behave when temperature, humidity and radon change on their own. We found two recent studies that name consumer models, each published in a peer-reviewed journal.

Two lessons carry over to a home. First, the averages of the monitors studied came reasonably close to a reference over weeks, which is the number that matters for a decision. Second, some monitors take many hours to react to a change, so an hourly figure on the screen can lag what is happening in the room. Neither study tested every model sold today, and neither is a rating of a brand.

An accurate monitor still gives a misleading answer if it runs for a few days in the wrong room. Radon levels vary from day to day and week to week, a few days can read much lower or much higher than your real average, and so a monitor should stay in place for at least 3 months.

1. 1Step 1 of 5:

   Pick the right room

   A room occupied for at least 4 hours each day, on the lowest lived-in level of the home. Not a kitchen, bathroom, laundry or storage room.

2. 2Step 2 of 5:

   Place it well

   Off the floor, away from an exterior wall, out of direct sunlight and away from air currents from heating and cooling vents, doors, fans and windows, and away from electronic or network devices. See where to place a radon test.

3. 3Step 3 of 5:

   Run it through the heating season

   At least 3 months, preferably in the heating season, when indoor levels are typically highest. Canada's guidance asks for at least 91 days of the test to fall in the heating season.

4. 4Step 4 of 5:

   Live normally

   Do not change how you live in the home during a long-term test.

5. 5Step 5 of 5:

   Decide on the long-term average

   Use the long-term average when deciding whether to mitigate. Each monitor averages differently, so read the maker's guide. If you have less than 91 days of data, follow up with a long-term radon test.

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Test	How long it runs	What it is for
Short-term test	Stays in the home from 2 to 90 days, depending on the device, and for a minimum of 48 hours.	A faster screening result. Because radon levels vary from day to day and season to season, it is less likely than a long-term test to tell you the year-round average.
Long-term test	Stays in the home for more than 90 days.	It is more likely than a short-term test to tell you the home's year-round average radon level.
Continuous monitor	Logs readings for the whole test, run as a short-term or a long-term test under the same durations in EPA guidance.	Logs a graph over time, so you can see trends and spot anomalies rather than a single number.

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C-NRPP's work answers a Canadian question against a Canadian guideline. U.S. guidance comes from EPA. EPA recommends fixing a home when the radon level is 4 pCi/L or higher. EPA recommends considering a fix when the level is between 2 and 4 pCi/L. In the United States, a short-term test stays in a home for two days to 90 days and a long-term test for more than 90 days, because radon levels tend to vary from day to day and season to season.

By those definitions, a consumer monitor that has run for more than 90 days has made a long-term measurement; before then, its average is a short-term one. If the result is for a home sale, check what the contract and your state accept before relying on a consumer monitor: C-NRPP does not approve these devices for use by radon measurement professionals. See radon testing and radon test kits.