Which test to use
There are two kinds of test, and the choice comes down to how quickly you need an answer.
- Short-term tests run from 2 to 90 days, and most run 48 to 96 hours. Charcoal canisters and continuous radon monitors both fall in this group. They are the normal choice for a first look and for real estate deals.
- Long-term tests run for more than 90 days, usually with an alpha-track detector. They give a better picture of the year-round average, since radon rises and falls with weather and season.
How to get a result you can trust
A short-term test is only as good as the conditions it ran under. EPA's closed-house conditions are simple, and they make a big difference:
- Keep windows and outside doors closed for at least 12 hours before the test and for the whole test, apart from normal coming and going.
- Do not run whole-house fans or anything else that pulls in a lot of outside air.
- Test in the lowest level of the home that is used or could be used as living space.
- Place the device at least 20 inches off the floor, in a room you use, away from drafts, exterior walls, heat and humidity. Avoid kitchens and bathrooms.
- Avoid testing during heavy storms or unusually high winds if you can help it.
- Write down the start and end time exactly as the kit instructs, and mail it the day it finishes. Charcoal kits lose accuracy if they sit.
Do it yourself or hire a tester
Minnesota homeowners can test their own homes with a kit. Many county public health offices list test kits, and MDH keeps a page of local radon contacts. For most people checking their own house, a kit is plenty.
A licensed professional with a calibrated continuous monitor is the better choice when other people are relying on the number, such as in a home sale, or when you want hour-by-hour readings. Anyone testing in a building they do not own or lease must be licensed by MDH. For questions, MDH's Indoor Air Unit is at 651-201-4601.
What your number means
Radon is reported in picocuries per liter of air, or pCi/L. EPA's action level is 4.0 pCi/L, and EPA suggests considering a fix between 2 and 4 pCi/L as well, since there is no known safe level. For context, MDH reports an average of 3.8 pCi/L across Minnesota from 2016 to 2025, compared with a U.S. average of 1.3.
One short-term result of 4.0 or higher should be confirmed before you spend money, unless you are in a real estate deal with a deadline. Use a second short-term test if you want an answer quickly, or a long-term test if you can wait. If the two results average 4.0 or higher, or the long-term test does, plan to fix the home.
Where you test matters. Test the lowest level you use or could use as living space, which in most Duluth homes is the basement, finished or not. A low result upstairs does not clear a basement you spend time in. If the house has more than one foundation type, each one should be tested.
Common mistakes that spoil a test
Most bad results come from small, avoidable errors. Opening windows on a mild day during the test will lower the result. Running a dehumidifier right beside the device, placing the kit on the floor, or setting it in a sump room or laundry area can skew it. Mailing a charcoal kit several days after finishing can invalidate it entirely. Read the instructions before you start, and pick a window of days when the house can stay closed.
Leave the device alone once it is running. Do not move it from room to room. If the test covers days when guests will be coming and going, normal entry and exit is fine, but doors should not be propped open. Operate the heating or cooling system normally. In a Duluth winter, closed-house conditions are usually easy to keep, which is one reason it is a convenient time to test.
When to test again
Test again after a mitigation system goes in, then at least every two years if you have a system. Retest after you finish a basement, replace the furnace or windows, or do any other work that changes how air moves through the home. If you have never tested and you are about to start using a lower level more often, test before you move in.
Common questions
What is the best time of year to test for radon in Duluth?
Any time works, but radon tends to run higher in the heating season because the house draws more soil gas. A winter short-term test is often a conservative one, and a long-term test averages out the seasons.
How much does a radon test cost?
Do-it-yourself kits commonly cost about $15 to $50, including lab analysis. A licensed tester with a continuous monitor costs more, so ask for a price when you call.
My neighbor tested low. Do I still need to test?
Yes. Results can differ widely between neighboring homes because of soil, foundation and how each house handles air.