Understanding Radon Testing

A guide to accurate testing and clear radon decisions
​Radon is a naturally occurring radioactive gas that can accumulate inside homes. Because levels vary widely — even between neighboring houses — the only way to know your home’s level is to test.
​This guide walks you through how to test correctly, how to interpret your results, and when mitigation is recommended. Everything here is based on established science and U.S. EPA soil gas mitigation standards.
1. What Testing Is
​Radon tests measure the concentration of radon gas in indoor air, expressed in picocuries per liter (pCi/L).
  • The U.S. EPA recommends mitigation at 4.0 pCi/L or higher.
  • Testing is simple, inexpensive, and the foundation for all mitigation decisions.
​​Good to know:
​Radon levels change naturally over time. A single test is a snapshot — not a lifetime measurement.
​2. Types of Radon Tests
​Short‑Term Tests (2–7 days)
​Most families start here.
  • Useful for quick decisions and real‑estate transactions.
  • Includes charcoal canisters and continuous radon monitors (CRMs).
  • Helpful for follow‑up testing after a long‑term test or mitigation.
​Long‑Term Tests (90+ days)
  • Best for understanding year‑round exposure.​
  • Smooths out seasonal fluctuations.
  • Provides the most stable picture of long‑term risk.
  • Recommended when short‑term results are borderline (2.0–3.9 pCi/L).
​Continuous Radon Monitors (CRMs)
​Professionally deployed electronic devices.
  • Provide hourly readings and tamper detection.
  • Required for post‑mitigation testing.
  • Useful when you want precise, time‑stamped data.
​3. How to Test Correctly
​Accurate placement matters more than most people realize. To ensure reliable results:​
  • Keep it 2–6 feet above the floor.
  • Avoid kitchens, bathrooms, and exterior walls.
  • Keep windows closed and doors closed except for normal entry/exit.
  • Avoid vents, fans, or drafts.
  • Follow all instructions on the test kit.
  • Place the test on the lowest regularly lived‑in level.
​If you’re unsure where to place the test, the Radon Navigator™ program can help you decide.
​4. How to Interpret Your Results
​0.0–1.9 pCi/L
​Radon is present but at low levels.
Retest every 2–3 years or after major renovations.
​2.0–3.9 pCi/L
​This is a borderline range. Consider:​
  • a confirmatory CRM test
  • a long‑term test
​Mitigation is reasonable if:
  • Someone in the home is a smoker.
  • Someone spends significant time on the lowest level.
  • You plan to finish a basement.
  • You prefer a more protective standard.
​4.0 pCi/L or higher
​Mitigation is recommended.
This is the EPA action level and the threshold used in real‑estate transactions.
​8.0 pCi/L or higher
​Mitigation should be scheduled promptly.
A confirmatory CRM test may be recommended to verify the level.
​5. When to Retest or Confirm
​You should retest if:
  • Your initial test was borderline.
  • The test was disturbed or placed incorrectly.
  • You recently renovated or changed HVAC systems.
  • You finished a basement.
  • You are preparing to sell your home.
​A confirmatory CRM test is recommended when:
  • The initial test is ≥4.0 pCi/L.
  • The result is unusually high or unusually low.
  • You want a more precise measurement before mitigation.
​6. When Mitigation Is Recommended
​Mitigation is recommended when:
  • Your test result is 4.0 pCi/L or higher.
  • You prefer a more protective standard.
  • You are finishing or remodeling a basement.
  • You are buying or selling a home and radon is part of the transaction.
​Mitigation is a one‑time installation with low operating costs and long‑term health benefits.
​Reassurance:
​​Radon‑related lung cancer risk builds over many years. You have time to make a thoughtful, informed decision.