Interpreting a Radon Test Result
Whether you used a short-term test kit or a continuous monitor, your result will come back as a number in picocuries per liter (pCi/L). This page explains what that number means, using the U.S. Environmental Protection Agency's own published guidance -- it does not tell you what to do about your specific home, and it is not a substitute for professional radon testing, diagnosis, or mitigation advice.
The EPA's action level
The EPA states that homes should be fixed if a radon test result reaches 4 pCi/L or higher -- this is what the agency calls the "action level." Below that, the EPA also states that homeowners should consider fixing their home for results between 2 and 4 pCi/L, because, in the agency's own words, there is no known safe level of radon exposure. The EPA's stated national average for indoor radon is approximately 1.3 pCi/L; average outdoor air is approximately 0.4 pCi/L, roughly a tenth of the action level.
Source: U.S. EPA, "What is EPA's Action Level for Radon and What Does it Mean?" (epa.gov/radon/what-epas-action-level-radon-and-what-does-it-mean), accessed 2026-09-03.
What "action level" does and doesn't mean
The action level is a threshold the EPA recommends acting on -- it is not a certified safety cutoff below which radon is confirmed harmless. The agency's own "no known safe level" language, quoted above, is explicit about this: it's a practical recommendation for when to act, not a claim that lower levels carry zero risk.
A single result at or near this threshold also doesn't automatically tell you what's causing it, or how to fix it. That's a separate question from simply reading the number.
A note on testing accreditation
You may see a test kit or monitor's packaging reference EPA involvement in radon-measurement accreditation. As this site's own review of the First Alert RD1 test kit found, the accreditation structure referenced on some older product packaging (an "EPA Radon Measurement Proficiency" program) is not the current structure: US radon-measurement device and lab accreditation is now administered primarily through the National Radon Proficiency Program (NRPP), operated under AARST and ANAB/ANSI accreditation -- a different body than the EPA action-level guidance cited above, even though both are legitimate, real programs. The EPA sets the health-based action-level guidance; NRPP is the body that currently accredits measurement devices and professionals. Conflating the two is an easy mistake this site aims not to make.
What this page does not do
This page explains the EPA's own published numbers and what "action level" means as a concept. It does not diagnose your home, does not recommend a specific mitigation approach, and is not a substitute for a qualified radon professional -- particularly for results at or above the action level, where the EPA's own guidance is to have the finding confirmed and to consult a qualified mitigation contractor. Silent Home Hazards has not independently verified the EPA's published figures against a primary regulatory filing beyond the agency's own public guidance page cited above; the numbers on this page are the EPA's own stated guidance, not this site's independent measurement or assessment.
Sources
- U.S. EPA, "What is EPA's Action Level for Radon and What Does it Mean?" --
epa.gov/radon/what-epas-action-level-radon-and-what-does-it-mean(government/primary source, accessed 2026-09-03) -- supports: the 4 pCi/L action level, the 2-4 pCi/L consideration range, the "no known safe level" statement, and the national average indoor/outdoor figures. - This site's own review of the First Alert RD1 radon test kit -- supports the NRPP/AARST accreditation-structure distinction, previously researched and cited there.
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