How Duluth compares
Minnesota has some of the highest radon levels in the country. MDH reports a statewide average of 3.8 pCi/L for 2016 to 2025, about three times the U.S. average of 1.3 pCi/L, and says 2 in 5 homes tested have radon at levels that are a major health risk. St. Louis County sits below the statewide share, but more than one in four properties tested there still reached the action level.
These results come from labs and radon professionals that voluntarily report to MDH. People who test are not a random sample of homes, so read the figures as a guide rather than a precise rate.
Why radon builds up here
MDH attributes Minnesota's high levels to the state's geology and cold climate. In winter, heating systems tend to draw radon gas from the soil, and Duluth's heating season is a long one. Warm air rising through a house creates a slight vacuum at the bottom of the home, which pulls in soil gas through any opening it can find.
That is why winter readings can run higher than summer readings in the same house, and why a home that has been tightened up with new windows or insulation is worth retesting.
Your neighbor's test does not tell you much
MDH is clear on this point: a home can have high radon whether it is old or new, well sealed or drafty, and with or without a basement, and houses next to each other can have very different levels. Soil, foundation cracks, sump pits, drain tile and the way a house handles air all play a part.
So the useful question is not whether Duluth has radon. It is what your house reads. A test takes a few days and usually costs little.
How to use these numbers
County figures are useful for one thing: deciding whether to test. They cannot predict a specific house. A share of 27% means roughly three in four tested properties came in under 4.0 pCi/L, but it also means a lot of homes did not, and you cannot tell which group yours is in from the street.
Remember who is in the data as well. Tests are voluntarily reported, and they include homes tested for a sale, homes tested out of concern, and possibly homes tested more than once. Hermantown, Proctor, Cloquet and Two Harbors have their own mix of soils and building types, and the same county-level figure does not capture block-by-block differences.
The Minnesota Department of Health publishes county data and test guidance, and your local public health office may have kits or advice. EPA's maps also classify counties into zones, but EPA itself cautions against using a zone to decide whether to test. Every home should be tested, whatever zone it falls in.
What to do next
The order of operations is short:
- Test the lowest level you use or could use as living space.
- If the result is 4.0 pCi/L or higher, confirm it with a second test unless you are on a real estate deadline.
- Between 2 and 4 pCi/L, consider a fix. EPA says there is no known safe level.
- If you need a system, get written quotes from Minnesota-licensed professionals.
- Retest at least 24 hours after the system starts, then at least every two years.
Common questions
Is St. Louis County a high radon area?
About 27% of properties tested from 2016 to 2025 measured at or above 4.0 pCi/L. That is lower than the statewide share, but it still means more than one in four tested properties reached the action level.
Do newer homes have radon?
They can. MDH says homes can have high levels whether old or new, and with or without a basement. The only way to know is to test.
Is winter the worst time for radon in Duluth?
Levels often rise in winter because heating draws more soil gas into the home. A long-term test gives a better picture of the year-round average.