EPA Radon Zones — what 1, 2, and 3 mean and when you should test

The three zones

Zone 1 (high risk): predicted average indoor radon screening level greater than 4 pCi/L. EPA recommends testing every home in Zone 1 counties.

Zone 2 (moderate risk): predicted average between 2 and 4 pCi/L. Testing is still recommended.

Zone 3 (low risk): predicted average less than 2 pCi/L. Testing is recommended for homeowners but not required.

Zone is not a guarantee

The EPA classification is a regional indicator based on geology and soil. It does not predict your specific home's radon level. Two adjacent houses on the same street can have wildly different readings depending on foundation type, ventilation, soil contact, and weather.

If you live in Zone 3 (low) you can still have elevated radon. If you live in Zone 1 (high) your home might be fine. Only an at-home test gives you address-level certainty.

How to test — short and long term

Short-term tests (2–7 days): inexpensive ($10–$30), good first screen. Works year-round but seasonally biased — winter readings tend to be highest because homes are sealed.

Long-term tests (90+ days): more accurate, captures seasonal variation. EPA recommends a long-term test after a positive short-term result.

Many state health departments offer free short-term test kits, especially in Zone 1 and Zone 2 counties.

When to mitigate

EPA action level is 4 pCi/L. At or above that, install a radon-mitigation system — typically a sub-slab depressurization pipe and fan, costing $800–$2,500 installed. The system vents soil gas to the roofline before it can enter the home.

Below 4 pCi/L but above 2 pCi/L: EPA recommends consideration of mitigation. Below 2 pCi/L: no action needed; retest in 2 years.