Guide for radon measurements in homes

About

This guide provides technical guidance for individuals and organizations carrying out long-term radon testing in low-rise residential buildings and individual units in multi-unit residential buildings (MURBs) (collectively referred to as homes in this guide). It provides information on how to measure radon levels in homes, for the purpose of comparing against the Canadian Radon Guideline level to make informed decisions about managing exposure and mitigation. Measurements taken following this guide will provide a reasonable estimate of a home's average annual radon level and assist with determining if mitigation is necessary.

The scope of this guide is limited to:

selection of radon measurement devices,
device placement,
measurement duration,
reporting, and
interpretation of measurements.

The Guide for Radon Measurements in Public Buildings is available for individuals looking to test radon in public buildings, such as workplaces, schools, daycares, hospitals, care facilities, and several units or building-wide measurements in MURBs.

More information:

Radon: Long-term test instructions (for homeowners)
Radon Resources

Radon

Radon is a naturally occurring radioactive gas formed by the radioactive decay of uranium in the natural environment. It is invisible and odourless, but radon measurement devices can easily detect it. When radon is released from the ground into the outdoor air, it is diluted and not a concern. In enclosed spaces, like homes, radon gas can accumulate to high levels and become a health risk.

The International Agency for Research on Cancer (IARC) has identified radon as a group 1 carcinogen. It is the number one cause of lung cancer for non-smokers in Canada. An individual's risk of lung cancer from radon depends on the concentration and duration of an individual's exposure. As such, individuals with long-term exposure to high radon levels are at greater risk of developing lung cancer.

Soil gas is the largest source of indoor radon. Radon can enter a home anywhere the building is in contact with the ground. Typical entry points include construction joints, gaps around service pipes, support posts, floor drains, sumps, or cracks in foundation walls and floor slabs (Figure 1). Radon will also move through the foundation. While higher radon levels are typical in basements and crawl spaces, elevated radon levels can be found throughout a home. Radon outgassing from water may be a potential source when a home's water supply is from a private well. Typically, radon from water does not affect indoor radon levels as much as radon from soil gas. Consequently, indoor air should be tested and radon from soil gas remediated before addressing radon from water sources.

Figure 1. This diagram illustrates radon movements inside and outside a building. — **Figure 1. This diagram illustrates radon movements inside and outside a building**

Radon gas is in all buildings in contact with the ground. Testing is the only way to know the radon level in a specific home and to determine if mitigation is necessary. Health Canada recommends every home should be tested, no matter where it is located, the type of building, or if it already has a mitigation system. Radon can vary widely between homes, even in homes in the same building, or buildings on the same street.

Canadian radon guideline

The Canadian Radon Guideline (the guideline) was established to help Canadians manage their risk of radon induced lung cancer. Health Canada collaborated with the Federal Provincial Territorial Radiation Protection Committee to review the health risk to Canadians from exposure to radon, using both a risk assessment and feedback obtained from a public consultation.

The guideline is as follows:

take corrective action if the average annual radon level exceeds 200 Bq/m³; in the normal occupancy area,
the higher the radon level, the sooner corrective action should be taken,
the corrective action should reduce the radon concentration as much as is practicable, and
the construction of new buildings uses techniques that minimize radon entry and will help remove radon after construction is completed, if necessary.

Note: 37 Bq/m³ is equal to 1 pCi/L

What to test with

There are many measurement devices available to test a home for radon. These devices work by measuring the alpha particles from the decay of radon and its decay products. There are many different detector technologies used in these devices, and they can generally be classified as either passive or active devices; both are available in Canada. The types of devices described below are currently recommended by Health Canada as acceptable for use with the measurement strategies described in this guide, provided they are C-NRPP approved devices. Only one (1) detector is required to perform a measurement in accordance with this guidance.

Health Canada recommends the use of long-term radon devices that have passed the Canadian National Radon Proficiency Program (C–NRPP) performance testing. C–NRPP provides a list of approved passive devices and professional-grade electronic radon monitors, as well as a list of approved consumer-grade electronic radon monitors. Both passive and active devices can provide accurate measurements when conducted according to the protocol outlined in this guide. Health Canada does not recommend the use of any specific device over another on these lists.

Passive radon devices

Passive radon measurement devices do not require an external power source or active sampling to measure indoor radon levels. These devices rely on the natural diffusion of radon into a detection chamber and measure the cumulative radiation from radon over the duration of the test. The collected signal from the radiation is read after the test is complete. Passive devices can only provide an average value of the indoor radon level over the test period.

The start and end dates must be recorded to at least the nearest day. These devices do not record time, so the start and end dates of the test must be manually recorded to know the test period of the measurement. Passive devices are easy for anyone to deploy, but require trained individuals to read the output and produce a report that reflects the average radon level over the course of the measurement.

Health Canada recommends two types of passive devices, alpha track detectors and electret ion chambers.

Alpha track detector

Alpha track detectors (ATD) contain a special plastic or film inside a filter-covered detection chamber. The chamber allows the entry of radon, while filtering out the entry of its decay products. Alpha particles released in the chamber from the decay of radon damage the plastic or film inside the device leaving damage tracks. The number of tracks correlates with the integrated radon level over the test period.

At the end of the test period, ATDs must be sent to a laboratory where the tracks are counted and analyzed to determine the radon level. The device should be sent according to the manufacture or lab instructions provided with the unit. Individuals should ensure that their test is completed before the manufacturer-specified expiry date to ensure accurate results. This expiry date is clearly labeled on the packaging or the device itself.

Health Canada recommends using long-term ATDs. Short-term ATDs are available, but short-term measurements are not appropriate for informing mitigation decisions.

Electret ion chamber

Electret ion chambers contain a positively charged disk (electret), in an electrically conductive plastic canister (chamber). During the measurement period, radon diffuses into the detection chamber with the exposed electret. Radiation emitted by radon and its decay products ionize the air molecules inside the chamber, reducing the electret voltage. The drop in voltage on the electret over a known time interval is measured and analyzed using specific calibrated readers to determine the average radon level. This is usually done through a qualified laboratory. The detectors are not destroyed during measurement or analysis, so these devices can be reused, and readings can be taken at specific intervals during the measurement period. The electret will need to be replaced once its voltage is below the usable level. Refer to manufacturer’s instructions to determine when to replace an electret.

Different types of detection chambers and electrets are available and should be used based on the measurement requirements. Refer to the manufacturer’s user manual to select the appropriate chamber and electret based on measurement requirements. Health Canada recommends using long-term electrets. Short-term electrets are available, but short-term measurements are not appropriate for informing mitigation decisions.

Active radon devices

Active radon measurement devices are electronic devices that continuously measure radon levels and provide near real-time readings. These devices sample air either through a small pump or natural diffusion into a detection chamber. Within the chamber, various technologies (alpha scintillators, ionization chambers, or solid-state detectors) detect alpha particles emitted by radon and its decay products. Active radon devices have on-board electronics and data processing features to measure, analyze, and report radon levels during the test. They can collect either independent or integrated measurements and provide discrete or averaged readings for specified time intervals.

The only active measurement devices recommended by Health Canada for long-term measurements are electronic radon monitors (ERMs). These devices can vary in terms of functionality, features, and usability; individuals should familiarize themselves with the capabilities and shortcomings of any ERM prior to use.

Electronic radon monitors

ERMs continuously measure radon levels at regular intervals and display results either directly on a digital screen, through smartphone applications, or through internet dashboards. Some ERMs can store readings for later evaluation or reporting and may also measure other environmental parameters such as temperature, humidity, and pressure. Before beginning a test, it is important to consider the device’s storage capacity. Some ERMs have less than 3 months of data storage space and may require periodic data downloads to ensure sufficient data are collected for a long-term test.

Health Canada recommends that users consider replacing ERMs five years after their purchase date to ensure that measurements remain accurate, unless they are recalibrated to manufacturer specifications.

Note: Many ERMs targeted at the public cannot be recalibrated after purchase.

Health Canada and the C-NRPP actively monitor the marketplace and conduct performance testing on ERMs. To help homeowners choose reliable devices for long-term radon measurement, C-NRPP maintains a list of ERMs on their website that have passed performance testing. Health Canada strongly recommends testing only with devices hat appear on the C-NRPP list. Devices that do not meet minimum performance requirements are recalled and listed on Government of Canada’s Recalls and Safety Alerts. Some devices may not appear on either list; this is typically because they are still undergoing testing or are subject to ongoing review or regulatory action.

There are also professional-grade ERMs that are more durable, responsive, sensitive, accurate, have a wider detection range, and have additional features or software relevant to professional applications. Professional-grade ERMs should be recalibrated by the manufacturer or a C–NRPP/NRPP accredited facility when required, to ensure reliable results. C–NRPP has a separate approval process for professional-grade ERMs and publishes a list of approved professional devices.

Note: Electronic Radon Monitors (ERMs) and professional-grade ERMs are updated terminology. ERM replaces the term Digital Detectors from previous versions of this guide and encompasses all current active radon measurement devices. Professional-grade ERM replaces the term Continuous Radon Monitor (CRM) from previous versions of this guide to emphasize their professional-grade quality and application.

This update reflects the advance of radon measurement technology, which has led to features that were once only in professional-grade ERMs (for example the capacity to provide hourly measurements or to record environmental parameters) now being found in ERMs for use by the public. Health Canada recommends using these updated terms when referring to active radon measurement devices to maintain clarity and consistency in communications and documents.

Note: C-NRPP categorizes ERMs as either consumer-grade or professional-grade, distinguishing devices intended to meet the needs of consumers from those designed for professional use.

How to test

It is important to consider the appropriate placement of radon measurement devices and timing, for measuring radon in homes. The goal of testing is to determine the average annual radon level in normally occupied areas of the home, for the purposes of making mitigation decisions. The criteria outlined below are intended to help achieve this goal.

When to test

Testing should be conducted so that a minimum of 91 days of the test is during the heating season. Testing conducted during the heating season will generally provide a conservative estimate of the annual radon level, as indoor radon levels are typically higher during colder months. This is primarily due to reduced ventilation from closed windows and doors, and increased entry of radon from soil caused by the stack effect. While it is possible to begin a long-term test at any time of the year, tests with fewer than 91 days during the heating season risk underestimating the average annual radon level and may require a re-test (see Interpretation of results).

Radon levels in homes vary over time due to factors such as residents’ habits, building ventilation systems and construction, entry pathways, prevailing weather conditions, daily and seasonal fluctuations, and more. In general, longer radon tests more accurately estimate the average annual radon level. To accurately determine the average annual radon level in a home, Health Canada recommends conducting radon tests over a period of 3 to 12 months.

Note: Residents should not alter their lifestyle during a long-term radon test.

What room to test

All measurements should be made in a normal occupancy area of the lowest lived-in level of the home. A normal occupancy area is defined as any space in which an individual spends more than 4 hours per day. Spaces that are not used daily but average this level of occupancy over the course of the year, or spaces that may become occupied soon should also be classified as normal occupancy areas , for example, renovating a basement for radon testing prior to add a bedroom, or changing how a space is used to add an office.

Note: Example of a space that is not used every day but may be considered a normal occupancy area: Anne works part time as an artist and spends a significant amount of time (12 hours a day) in her basement studio on most weekends. She also spends a few hours during the week in her basement. Even though she is not spending 4 hours each day in the basement, the average time spent in the basement over a year is greater than 4 hours per day and the basement would be considered a normal occupancy area.

Ideal measurement locations include:

family rooms,
living rooms,
dens,
playrooms,
offices, and
bedrooms.

Bedrooms on the main floor or basement should be prioritized; residents generally spend more time in their bedrooms than in any other room in the house. If children are in the home, areas such as basement-level playrooms should be tested.

Note: The basement is only considered a potential measurement location if it includes a normal occupancy area.

Tests should not be conducted in the:

kitchen,
laundry room, or
bathrooms.

These locations are not appropriate to conduct radon tests, as they typically have different air quality and ventilation characteristics compared to the rest of the home. In homes with open floor plans, individuals should choose a location in the living area of the open space and avoid the previously mentioned areas.

Figure 2. Potential rooms for radon testing locations in a home. Locations that are appropriate (✓) for radon testing, such as a bedroom, living, or office, and locations that are not appropriate (✘) for radon testing, such as a kitchen, bathroom, or storage room, are indicated.

Where to place a device

When choosing a place for the device within a room, considerations should be made to ensure that the device is not disturbed or lost. Select a place that is out of the reach of children or pets. Place the device in the approximate breathing zone, with access to the main air space, following the placement criteria below.

Note: Examples of appropriate places for a measurement device include a shelf, end table, dresser, or suspended from the ceiling.

ERMs may have limited placement options due to being connected to a wall socket or a power cable. In these situations, users should follow the placement criteria to the extent that is reasonably possible and any specific placement instructions from the manufacturer. Before starting a test, always make sure to reset ERMs and install new batteries (for battery operated ERMs) to prevent any loss of power during the measurement period.

**Figure 3. Potential detector placement in a room. Locations that are appropriate (✓) for radon testing and locations that are not appropriate (✘) for radon testing are indicated.**

Placement criteria

For more specific recommendations relating to the placement of measurement devices, refer to Appendix II - placement specifics.

Do:

✔ Place the device where it will not be disturbed.
✔ Allow space for air flow around the device.
✔ Place the device in an area occupied for four or more hours per day.
✔ Place the device on the lowest lived-in level of the home.
✔ Wipe the surface with a dry cloth before placing the device.

Do not:

✘ Place the device in contact with the floor, ceiling, or exterior wall.
✘ Place the device in enclosed spaces such as a closet or drawer.
✘ Place in areas with high humidity such as in sunrooms, near humidifiers, or in bathrooms.
✘ Place the device near heat sources or in direct sunlight such as near a fireplace, on a windowsill, or over a radiator.
✘ Place the device near air currents caused by heating, ventilation, and air conditioning systems such as on a vent, near a door, or near windows.
✘ Place the device directly next to or on electrically powered devices or network appliances such as computers, Wi-Fi routers, television sets, stereos, or speakers; as some measurement devices may be affected.
✘ Place the device near typical radon entry points that may artificially increase measured levels, and are not representative of the typical breathing zone such as near sump holes, in crawl spaces, or next to exposed cracks in the foundation.

Other considerations

Damaged devices: If the device is dropped, broken, or potentially compromised in any way, individuals should contact the manufacturer for further information and guidance. Alternatively, users can choose to repeat the test with a new device.

High or unusually low readings from ERMs: If an ERM reports hourly or other short-term radon readings that are close to either the upper or lower measurement limits specified in the detector’s manual (for example, a functional range of 7 – 3700 Bq/m³), contact the manufacturer for guidance. Readings near these limits may indicate that the device is operating outside its intended range, and the values should be verified. When the measurement range is exceeded, the device may display the same value for multiple consecutive readings.

Floors above ground level: Homes where the lowest lived-in level is not in contact with the ground should still be tested. Although these homes typically have lower radon levels, they can still have a level above the guideline.

Homes with mitigation systems: Homes with mitigation systems should still be tested when there are no recent measurements available. Although these homes typically have lower radon levels, they can still have a level above the guideline, and may require further corrective action. The only way to determine the efficacy of a mitigation system is by testing. Health Canada recommends that homes with active mitigation systems should be retested every 5 years to ensure the system is functioning as intended.

Loss of power: If an ERM loses power during a measurement, individuals should check the integrity of the measurement data. If the data is still intact, then the measurement can continue once power to the device is restored. If not, it may be necessary to start the testing period over again. Some battery operated ERMs do not preserve data in the case of loss of power. It is important to use new batteries when starting a test with a battery-operated ERM. ERMs that require removable, external, or cloud storage should be set up according to manufacturers' instructions.

Using a single device to test multiple locations: ERMs and electrets can be used to test multiple locations. It is important to reset the device before testing a new location with an ERM, and to follow the protocol provided in this test guide.

Quality assurance / quality control: Professionals conducting radon measurements and laboratories analyzing radon measurement devices should comply with C–NRPP’s Quality Control and Quality Assurance Manual for Radon Sampling and Analysis conducted by Radon Measurement Professionals and Laboratories.

Reporting and interpretation of results

Report criteria

After a completed test, a report should be provided detailing the results of the test . Depending on the device and company used, these reports may be created in a number of different ways. The report must be clear, easy to understand, and provided in a digital or physical format as requested by the individual.

Note: Report criteria are defined for radon measurement laboratories and professionals to present results to their clients. This section does not apply to individuals who do their own testing using ERMs, where it may not be possible to generate a detailed report for their test.

Basic report content

The report should have the following information:

Date the report was issued.
Complete physical address of the home where the measurement was taken.
Start and end date of the measurement.
Results of the measurement reported in Bq/m³ for the measurement period:
1. with the uncertainty of the measurement in Bq/m³; or,
2. if the result is less than the limit of detection or quantification, the limit should be reported instead with a statement the result is below that specific limit.
A comparison of the measurement result to the guideline level and the recommended action as per the guideline.
If it can be determined that any of the conditions in Table 1 occurred during the measurement period, then the appropriate disclaimer should be included.

Table 1: Testing conditions that may impact the validity of the measurement
Condition	Example disclaimer
The test period is less than 91 days.	This test was less than 91 days; Health Canada recommends that measurements occur over a time period no less than 91 days. Shorter test periods may not be sufficient to estimate an annual average. A new test is recommended.
The radon measurement device was tampered with or damaged.	The radon measurement device was compromised prior to analysis. The results of this test may not be representative of the location. A new test is recommended.
Fewer than 91 days of the test occurred during the heating season.	This measurement is still representative of the radon level over the test period. However, testing periods that occur in part or wholly outside the heating season may underestimate the average annual radon level. See “Interpretation of results” for how to use your result for decisions on retesting or action.
Location and placement of the radon measurement device deviated from the guidance.	The placement of the radon measurement device deviated from Health Canada's placement guidance. This measurement is still valid for the location that was tested. However, devices placed in non-standard locations may not provide a sufficient estimate of an average annual radon level.

Supplementary report content

A report should have the following information if appropriate:

Name and contact information of all certified professionals or companies that conducted the measurement or analysis.
Room and floor where the device was placed in the home.
Serial number or identification number of the device used for the measurement.
Type, manufacturer, and model of the device used for the measurement.
Information on the validity of the device (for example, expiry date of the ATD, calibration date of professional grade ERM).
Photos of the device serial number, and of the device in the test location.
Statement of the Health Canada radon guideline.

Interpretation of results

Following the measurement protocols outlined in this guide provides an estimate of an individual’s average annual radon level in their home. All residents of the home should be informed of the radon level they are being exposed to. Only the long-term average value should be used for comparing to the guideline. You may need to get this value differently depending on your measurement device:

Passive radon measurement devices, properly deployed, provide this value in the laboratory report and can be compared directly with the guideline.
Active radon measurement devices (such as ERMs) are often capable of displaying various measurement periods and statistics. Use the long-term average value to compare with the guideline.
Some ERMs do not report long-term averages; the long-term average radon level can be determined using the calculations in Appendix III – sample calculations. The calculated long-term average value can then be compared with the guideline.

If a measurement is above the Canadian Radon Guideline level, the building owner should take steps to reduce the exposure of all residents. Health Canada recommends:

Individuals mitigate within 1 year for radon levels higher than 200 Bq/m³.
Individuals take action sooner if the radon level is higher.
Mitigation measures should reduce the radon level in the home to as low as reasonably achievable (ALARA).

These recommendations apply to tests conducted for a duration of 91 days or more at any time during the year.

While the health risk from radon exposure below the Canadian Guideline is small, there is no level that is considered risk free. It is the choice of each individual to decide what level of radon exposure they are willing to accept. Regardless of radon level, any action taken that reduces an individual’s radon exposure corresponds to a decrease in their health risk.

Individuals can find more information on corrective actions and mitigation solutions in the Radon – Reduction Guide for Canadians or by contacting a C-NRPP certified Radon Mitigation Professional.

Note: When interpreting radon test results, it is important to understand that all measurements include some amount of uncertainty. This means that if you repeated the test under the same conditions, the results might come out slightly different. For radon detectors, North American standards from the Canadian Standards Association (CSA) and the American National Standards Institute (ANSI) consider it acceptable for repeated results to vary by up to ±25%. In practical terms, if a radon test result is slightly below the 200 Bq/m³ guideline level, the true value may be just over the guideline. Similarly, if your result is slightly above 200 Bq/m³, the actual radon concentration may be below the guideline.

Re-testing

If fewer than 91 days of your test occurred during the heating season and you obtained a measurement below 200 Bq/m³, it may be underestimating your average annual radon level and you should re-test during the next heating season.

Follow-up radon testing may be necessary in other cases. Health Canada recommends individuals re-test their home the next heating season in the following situations:

After any renovation that affects the structure or ventilation of the home (for example renovating the basement, installing a new furnace, adding a bathroom).
After energy retrofits to the home to make it more energy efficient (for example installation of new windows, insulation, sealing).
After any significant excavation or earthwork adjacent to the home (for example replacing a septic tank, exterior waterproofing, terracing, installing drainage systems).
Following any new noticeable structural damage to parts of the home in contact with the ground (for example, concrete slab and basement walls).
If the basement or main floor was not tested and has since become the lowest lived-in level of the home.
After any radon mitigation system is installed, to ensure performance of the system.
In a newly built home, 2 years after year of construction; note that the home should still be tested the first heating season after occupancy.
If an active soil depressurization system is installed, the home should be tested every 5 years to ensure the system is continuing to function as intended.

Appendix I - Frequently asked questions

Question: What should I do if my test (using a passive measurement device) has lasted longer than 12 months?
Answer: You should contact the manufacturer or laboratory to determine if the measurement is still valid.

Question: I live above the second floor in an apartment building, should I test?
Answer: Homes above ground level should still be tested. Although, these homes typically have lower radon levels, there is still a risk that it could exceed the guideline level.

Question: I moved into a home that has a mitigation system installed. Do I still need to test?
Answer: Health Canada recommends that everyone test their home. If you don’t know the radon level in your home, you should test. Additionally, Health Canada recommends that homes with active mitigation systems should be retested every 5 years to ensure the system is functioning as intended.

Question: I have been testing with an ERM and noticed some values above the guideline (200 Bq/m³). However, my test so far has been less than 91 days. What should I do?
Answer: The 200 Bq/m³ guideline applies to your average annual radon level, not short-term measurements. The minimum test length is 91 days for a valid estimate of the average annual radon level. Health Canada recommends making decisions for corrective action based on tests which are at least 91 days in length.

Question: I’ve been testing with an ERM. Sometimes my hourly or seasonal radon levels go above the guideline (200 Bq/m³), but my long-term average (greater than 91 days) is below the guideline. What should I do?
Answer: Radon levels naturally rise and fall due to a variety of factors, so short-term variations above 200 Bq/m³ are possible. Decisions should be based on the longest and most representative average you have. This could be a full 12-month measurement, or at minimum a long-term test of more than 91 days – keep in mind that additional testing may be required if less than 91 days of the test occurred during the heating season.

Question: I tested for 91 days, but not entirely during the heating season (for example, beginning in Spring/Summer and ending in Summer/Fall). Should I re-test?
Answer:

If you measured below the guideline (200 Bq/m³): Yes – you should re-test so that at least 91 days occurs during the heating season. Tests with fewer than 91 days during the heating season may underestimate the average annual radon level in your home.
If you measured above the guideline (200 Bq/m³): No – a re-test is not necessary. You should follow Health Canada’s recommendation to take action to reduce radon levels in your home.

Appendix II - Placement specifics

The requirements below represent best practice for device placement. In the event that it is not feasible or reasonable to fully implement these specifications, Health Canada recommends following them to the extent possible. Radon measurement device placement should be:

in a room on the lowest level of the home with a normal occupancy area such as a bedroom, office, playroom, living room in a basement or main floor.
in a place where the device will not be moved during the measurement period.
in the typical breathing zone (at least 30 cm, or 1 ft, above the floor).
at least 30 cm from walls or ceilings.
in a place which falls within the manufacturer's recommended range for temperature, humidity, and pressure. Typical ranges for these parameters are as follows:
- Temperature: 0 to 35°C (32 to 95 °F)
- Relative humidity: below 80%
- Pressure: 70 to 110 kPa (10 to 16 PSI)
at least 1 m away from vents, windows, doors, or anything that may interfere with normal airflow.
away from electronic or network devices, which may affect measurements.
away from objects to allow normal airflow around the device, except the surface the device is placed on or mounted to. Health Canada suggests a minimum of 10 cm (4 in) between the device and other objects.

Appendix III - Sample calculations

This appendix provides detailed methods for calculating the arithmetic average radon concentration over a given time period. These calculations are applicable for situations where ERMs do not provide a long-term average and only shorter-term measurement data are available (for example, hourly measurements instead of a long-term average value). Average radon concentrations calculated using the methodology below can be directly compared to the guideline value of 200 Bq/m³ for decision-making purposes, provided they meet the other testing requirements in this guide.

Individuals are reminded that Health Canada does not recommend testing for periods shorter than 91 days. The 8 hour period used in the sample calculations is for demonstrative purposes only and should not be interpreted as an appropriate test duration.

For equal time intervals

To calculate the average radon concentration for this period, a simple average (Equation 1) can be used to calculate the long term average from smaller interval measurements.

Equation 1: Calculation for the average long-term radon concentration when the measurement intervals are all equal. This is calculated by dividing the sum of all interval radon measurements by the number of intervals. Where Rn_i is the radon measurement for the interval, n is the number of intervals, and Rn' is the long-term average radon concentration.

A sample dataset is provided for this calculation below.

Table 2: Sample data showing radon measurements taken every hour over 8 hours
Date	Time	Interval duration (hours)	Radon (Bq/m³)
June 10^th, 2024	11:00 am - 12:00 p.m.	1	144
June 10^th, 2024	12:00 p.m. - 1:00 p.m.	1	159
June 10^th, 2024	1:00 p.m. - 2:00 p.m.	1	159
June 10^th, 2024	2:00 p.m. - 3:00 p.m.	1	177
June 10^th, 2024	3:00 p.m. - 4:00 p.m.	1	157
June 10^th, 2024	4:00 p.m. - 5:00 p.m.	1	190
June 10^th, 2024	5:00 p.m. - 6:00 p.m.	1	182
June 10^th, 2024	6:00 p.m. - 7:00 p.m.	1	215

To calculate the average radon concentration for this period, sum the individual hourly measurements and then divide by the number of intervals during the test.

**Figure 4. Example calculation when measurement intervals are equal**

Defined terms

Active soil depressurization system: A radon mitigation system that reduces the radon level in a home. The system removes the air pressure difference between the house and soil, and exhausts the soil gas outside using a fan.
Average annual radon level: The average radon level in a home, calculated over a twelve-month period.
As low as reasonably practicable/ As low as reasonably achievable (ALARP/ALARA): The principle that radiation exposure should be as low as possible using reasonable effort and weighing the social, economic, and technological costs and limitations with the health benefits. While the guideline level for mitigation is 200 Bq/m³, it is expected that mitigation measures will reduce radon to levels that are ALARA. The Guideline level of 200 Bq/m³ is not a recommended stopping point for mitigation if it is reasonable to go lower, with social, economic, technological, and other factors considered.
Becquerel (Bq): International System unit for radioactivity. One becquerel corresponds to one nuclear decay per second. For radon gas, one becquerel is one nuclear decay of radon, emitting one alpha particle (a form of ionizing radiation) per second.
Becquerel per cubic metre (Bq/m³): International System unit for the concentration radioactive decay in air. One cubic metre (m³) is equal to 1000 litres.
Breathing zone: The summation of all space where residents typically breathe (i.e., the region around their face and immediately adjacent). The zone will depend on the use of the room (for example: bedroom vs. living room) and the physical characteristics of the individuals using the room (for example: children vs. adults). Typically this zone is considered from 0.3 m to 2.5 m from the floor of the room.
Corrective action / Mitigation action: An action to reduce the indoor radon level to as low as reasonably practicable.
Group 1 carcinogen: A substance that causes cancer; there is sufficient evidence of the substance causing cancer in humans. This is a classification by the International Agency for Research on Cancer used to evaluate the strength of evidence for cancer-causing substances.
Guideline level: A threshold radon level at which corrective action is recommended. Determined by the Canadian Radon Guideline to be 200 Bq/m³. This is also referred to as Canada's national reference level.
Heating season: A period of time during the year when home heating appliances are used to supply heat to a room or space directly. This time period can span different durations depending on the region and climate patterns, but generally coincides with the colder months of the year.
High radon level: A radon level that exceeds the guideline reference level of 200 Bq/m³.
Home: A low-rise residential building or a single unit in a multi-unit residential building.
Home heating appliance: Any appliance that is used to heat a home. This includes all fixed, and non-fixed appliances that are used to heat a home, or a space within the home.
Lived-in level: The floor or story of a home with a normal occupancy area.
Long-term radon test: A radon measurement that spans a time period of at least 91 days.
Low-rise residential building: Building intended for private occupancy with up to and including four stories in height.
Mitigation: Action to reduce the indoor accumulation of large amounts of radon.
Multi-unit residential building (MURB): Residential building that contains two or more units intended for private occupancy.
Normal occupancy area: Any area occupied by an individual for more than 4 hours per day. Spaces that are not used everyday, but on average, over the course of the year, are used for this same amount of time may also be defined as normally occupied.
Outgassing: The release of a dissolved, frozen, or trapped gas from solid or liquid material.
Radon level: The concentration of radon gas in air, measured in Bq/m³.
Residential building: A building intended for private occupancy.
Short-term: Time period that is less than 91 days.
Soil gas: Gas found in pore spaces of the soil.
Stack effect: Air movement resulting from temperature differences. As warmer air rises due to its lower density, which is forced out of the home, the lower levels of the home become depressurized. This allows cooler air from the ground and outdoors to enter the lower floors of a home. This effect is strongest during the heating season.

List of acronyms

ATD: Alpha-track detector
ALARA: As low as reasonably achievable
ALARP: As low as reasonably practicable
ANSI: American National Standards Institute
CARST: Canadian Association of Radon Scientists and Technologists
C-NRPP: Canadian National Radon Proficiency Program
CRM: Continuous radon monitor
CSA: Canadian Standards Association
ERM: Electronic radon monitors
MURB: Multi-unit residential buildings

Acknowledgements

Health Canada would like to acknowledge the Canadian Association of Radon Scientists and Technologists (CARST) for the support and collaboration they provided during the development of this guide. The invaluable studies conducted by CARST support the guidance by Health Canada. Health Canada would like to dedicate this guide to Adelene Gaw. Adelene was an exceptional member of the radon and radiation protection community, and was instrumental to the development of this version of the radon testing guide.

Page details

2026-05-22

Choose a theme