Radon Levels Guide

Radon in Delaware: Levels by County and EPA Zones

Updated November 2026 · Data: EPA Map of Radon Zones · Sources

No Delaware counties are in EPA Zone 1, but 1 of 3 are in Zone 2, where the predicted average indoor radon level is between 2 and 4 pCi/L. The Delaware Radon Program reports that about 15% of homes tested in New Castle County are above the EPA action level, compared with generally less than 10% in Kent and Sussex counties. Find your county below, then learn how to test your home and what to do if the result is high.

0 of 3counties in EPA Zone 1 (highest potential)
1 of 3counties in Zone 2 (moderate)
2 of 3counties in Zone 3 (low)
~15%of New Castle County homes tested above 4 pCi/L (state fact sheet, 2022)

Your county’s zone is not your home’s radon level. Homes with high radon are found in every zone. The EPA recommends testing every home, whatever its zone.

Radon zones by county in Delaware

The table lists the EPA radon zone for each of the 3 counties in Delaware. The zone shows the predicted average indoor radon screening level for homes in that county.

CountyEPA zonePredicted average indoor level
KentZone 3Below 2 pCi/L
New CastleZone 22 to 4 pCi/L
SussexZone 3Below 2 pCi/L
Source: U.S. EPA Map of Radon Zones (data file published June 2024).

What the EPA radon zones mean

  • Zone 1 (highest potential): predicted average indoor screening level greater than 4 pCi/L. In Delaware: 0 counties (0%).
  • Zone 2 (moderate potential): predicted average between 2 and 4 pCi/L. In Delaware: 1 county (33%).
  • Zone 3 (low potential): predicted average below 2 pCi/L. In Delaware: 2 counties (67%).

The EPA built the map from indoor radon measurements, geology, soil permeability and type of house foundation. It was made to help governments and builders target resources, not to decide whether a single home needs testing.

How to test for radon in Delaware

Testing is the only way to know your home’s radon level. Short-term test kits (2 to 90 days) are sold at hardware stores and online, and some state programs offer kits at low cost; check with the Delaware Radon Program (Division of Public Health). Test in the lowest lived-in level of the home, with windows and doors closed, and follow the kit instructions.

  • Do-it-yourself kits: a simple, low-cost first step for your own home.
  • Long-term tests (more than 90 days): give a better picture of your home’s year-round average.
  • Certified professionals: look for certification from the National Radon Proficiency Program (NRPP) or the National Radon Safety Board (NRSB), and ask the state program whether Delaware requires a state license.
  • Buying or selling a home: ask for a radon test as part of the home inspection.

If your radon level is high

The EPA recommends fixing your home if the radon level is 4 pCi/L or higher, and considering a fix between 2 and 4 pCi/L. The most common fix is a radon mitigation system (sub-slab depressurization), which pulls radon from under the foundation and vents it outside, above the roof line.

  • The EPA says most homes can be fixed for about the same cost as other common home repairs; the price depends on the size and design of the home.
  • Get estimates from more than one qualified, certified mitigation contractor. See our radon mitigation cost guide for typical prices.
  • Test again after the system is installed, and retest every few years.

Delaware radon program

The Delaware Radon Program (Division of Public Health) answers questions from residents about radon testing, results and certified professionals.

Contact details as listed by the state radon program directory. Please confirm on the program’s website before calling.

Frequently asked questions

Is radon a problem in Delaware?

None of Delaware’s 3 counties are in EPA Zone 1, but high radon levels can be found in any home, in any zone. Testing is the only way to know your level.

Do I need to test if my county is in Zone 2 or 3?

Yes. The EPA zones show predicted averages for large areas, and they were not designed to decide whether a single home needs testing. The EPA recommends testing every home.

What radon level is safe?

There is no known safe level of radon. The EPA recommends fixing your home at 4 pCi/L or higher and considering a fix between 2 and 4 pCi/L.

Who can I contact about radon in Delaware?

The Delaware Radon Program (Division of Public Health) answers questions about testing, results and certified professionals. Phone: 302-744-4816; 1-800-464-4357.

Sources