When Do I Use Two or More Monitors for a Radon Test: Optimal Strategies for Reliable Measurements



Radon testing in your home is crucial for ensuring a safe living environment as radon is a colorless, odorless gas with significant health risks. The Environmental Protection Agency recommends action when radon levels reach or exceed 4.0 pCi/L (picocuries per liter of air). In certain situations, using multiple monitors for a radon test can yield a more accurate assessment of your home’s radon levels.

To decide when multiple monitors are necessary, consider both the size and layout of your home, and the purpose of your radon testing. For example, if you’re conducting radon testing for a real estate transaction, time-sensitive tests may require the additional data that multiple monitors can provide to ensure a thorough evaluation. Conversely, if you are testing radon levels in different areas of your home, such as the basement and living areas, using more than one monitor will help you determine the variance in radon concentrations throughout your home.

Furthermore, utilizing several monitors also helps in verifying the accuracy of your radon readings, especially when dealing with lower levels of radon. By comparing the readings from multiple units, you can get a closer approximation of the true radon level and make better-informed decisions about whether mitigation is necessary. It’s essential to ensure that the equipment you’re using adheres to the local guidelines and to employ qualified professionals for radon mitigation if high levels are detected.

Determining the Need for Multiple Monitors

When conducting a radon test, especially with a radon tester for professionals, the decision to use multiple monitors is critical to ensure accurate and representative results. The size and layout of the testing area can significantly influence radon concentrations.

Assessing Room Size and Configuration

For rooms larger than 2,000 square feet, it’s advisable to use additional monitors to cover the area effectively. Radon levels can vary from place to place due to factors such as ventilation, foundation integrity, and soil composition. In complex room configurations—like those with multiple levels or areas separated by walls—a single monitor may not provide a complete picture of the radon situation. In such cases, place monitors in the highest risk areas, such as basements and ground floor rooms.

Additional test locations are specifically recommended for:

  1. Each area that exceeds 2000 square feet (189 square meters) on the level of the home being tested:
  2. Each area of the home is served by a different heating and cooling system; and
  3. Each unique foundation area. This recommendation includes a split-level foundation or where slab-on-grade rooms attach to a basement or crawl space area. One test location may not be representative of radon concentrations in other areas of the home.

Check ANSI/AARST MAH-2023 standard here.

Understanding Radon Variability and Testing Goals

Radon levels can fluctuate due to environmental changes like the weather and can be influenced by the building’s HVAC system. For a thorough assessment, multiple measurements can offer a more consistent and accurate reading. The goals of the test, whether for a real estate transaction or health concerns, also dictate the extent of monitoring. If the goal is to get a comprehensive understanding of radon distribution across the entire space, deploying multiple monitors is extremely beneficial.

Implementing Multi-Monitor Radon Tests

When conducting  Radon testing in Apartment Buildings, Schools, or mixed-use buildings detailed test plans considering a multitude of conditions are necessary. Such test plans are governed by testing standards professional radon testers follow such as ANSI/AARST MA-MFLB-2023, which is specifically targeted for those applications

Selection and Placement of Monitors

  • Choose Appropriate Monitors: Opt for continuous radon monitors (CRMs) for precise readings. The American Radon Mitigation explains that CRMs are calibrated digital devices, designed for professional use.
  • Placement Strategy: Determine high-priority areas such as basements and ground-floor rooms. Place monitors at least 20 inches above the floor, away from doors, windows, and exterior walls.
  • Avoid Interference: Ensure that each monitor remains undisturbed during the testing period to prevent data disruption.

Interpreting Test Results from Multiple Locations

  • Comparative Analysis: Evaluate the radon levels recorded by each monitor. If readings vary significantly, investigate potential causes such as ventilation differences.
  • Take Action: Should any monitor display radon levels above the action threshold set by the US EPA at 4.0 pCi/L, consider immediate remediation steps across the property.


When considering radon testing for your home, multiple monitors can be beneficial under certain circumstances. If you’re conducting a radon test in a large or irregularly shaped home, using two or more monitors will help provide a more accurate assessment of radon levels across different areas. Remember that radon fluctuations occur, and testing over an extended period gives a comprehensive overview of your exposure. Ultimately, ensuring the safety of your living environment is paramount; therefore, employing multiple monitors in the advised situations aids in obtaining precise data to make informed mitigation decisions.

When Do I Use Two or More Monitors for a Radon Test: Optimal Strategies for Reliable Measurements was last modified: by