Radon is invisible, odorless, and generally not something homeowners think about unless a home inspection flags it during a purchase. But it's worth putting on your own recurring maintenance calendar rather than treating it as a one-time box to check, because the conditions that let radon into a home can change over time even when nothing looks different on the surface.
How often to test
EPA and the Surgeon General recommend testing every home for radon, and retesting roughly every 2 years, since a house settles over time and new entry routes for soil gas can open up that weren't there when you first tested. You should also retest after any major renovation, after adding or changing HVAC systems, or if you're moving into a home that hasn't been tested recently regardless of when a previous owner may have tested it.
If you've already had a mitigation system installed because of a prior high reading, EPA guidance calls for retesting the following winter after installation (waiting at least 90 days), and then periodically after that to confirm the system is still working as intended.
The action level that actually matters
EPA's action level: 4 pCi/L: EPA recommends taking action to reduce radon levels when a test comes back at or above 4 picocuries per liter (pCi/L). This is the specific number to compare your test result against — a reading below that level doesn't mean zero risk, since radon has no fully safe threshold, but 4 pCi/L is the point EPA specifically recommends fixing.
Why this is worth taking seriously
EPA identifies radon as the leading cause of lung cancer among people who have never smoked, and the second leading cause of lung cancer overall after smoking itself. EPA's estimates attribute roughly 21,000 lung cancer deaths per year to radon exposure, including around 2,900 among people who never smoked. These figures trace back to EPA's broader risk assessment work, which itself draws on the National Academy of Sciences' BEIR VI report — worth knowing if you want to trace the underlying science, since it means the specific numbers reflect an assessment methodology rather than a single simple measurement.
How testing actually works
- Short-term test kits (2-90 days) give a faster initial read and are widely available at hardware stores or through your state radon program.
- Long-term test kits (more than 90 days) give a more representative picture of your home's year-round average, since radon levels can fluctuate with weather and season.
- Place the test kit on the lowest lived-in level of the home, away from drafts, exterior doors, and windows, following the kit's specific instructions.
- If your result comes back at or above 4 pCi/L, EPA recommends a follow-up test to confirm before proceeding to mitigation, since results can vary.
- If mitigation is installed, retest afterward to confirm the reduction actually worked, rather than assuming installation alone solved the problem.
This is a genuinely recurring task, not a one-time inspection item
Because radon entry can change with foundation settling, seasonal soil conditions, and renovation work, treat testing as something that belongs on your maintenance calendar on a roughly 2-year cycle rather than a single checkbox from your home purchase inspection years ago.
Radon levels can also vary meaningfully between different areas of the same home, and even between similar homes right next door to each other, because soil composition and foundation-specific entry points differ more than most people expect. This is part of why EPA doesn't rely on regional radon maps alone to tell homeowners whether to test — a neighborhood generally considered low-risk can still contain individual homes with elevated readings, and a high-risk area can contain homes that test well below the action level. Testing your own home directly is the only way to know your actual number, regardless of what a zone map or a neighbor's result suggests.
It's also worth testing after any change to how air moves through the house — sealing up drafts for energy efficiency, adding a new HVAC system, or finishing a basement can all change the pressure dynamics that influence how much soil gas gets pulled indoors. None of these projects are reasons to avoid the improvement itself, but each is a reasonable trigger to retest afterward rather than assuming your last result still reflects the home's current condition.
What radon level requires action?
EPA recommends taking action to reduce radon levels when a test result comes back at or above 4 picocuries per liter (pCi/L). A reading below that level doesn't mean zero risk, since radon has no fully safe threshold, but 4 pCi/L is the specific point EPA recommends as the trigger for mitigation.
How often should I retest my home for radon?
EPA and the Surgeon General recommend retesting roughly every 2 years, since a home settles over time and can develop new entry routes for soil gas. You should also retest after any major renovation, after HVAC changes, or when moving into a home regardless of a previous owner's test history.
Why is radon considered such a serious health risk?
EPA identifies radon as the leading cause of lung cancer among people who have never smoked and the second leading cause of lung cancer overall after smoking. EPA's estimates attribute roughly 21,000 lung cancer deaths per year to radon exposure, including around 2,900 among people who never smoked.
Do I need to retest after installing a radon mitigation system?
Yes. EPA guidance calls for retesting the following winter after installation, waiting at least 90 days, and then periodically after that to confirm the mitigation system continues working as intended rather than assuming installation alone permanently solved the problem.