Radon test? Close your windows. ALL of them. Please and thank you.

If you’re selling a home in Minnesota, odds are the buyers will order a radon test. We do radon tests at over half of our home inspections; the exact number was 55% in 2025. To help prevent delays, frustration, and suspicion, it’s important to follow the rules for radon testing. When the rules aren’t followed, the test isn’t valid. An invalid radon test will usually in a re-test, which will typically take another three days. Nobody wants to deal with that, but we see it happen several times a week.

Rules for Radon Testing in Minnesota

Before we conduct a short-term radon test, we pass the rules along to the seller. At least, we do our best. We typically don’t have direct contact with the sellers; we go through their real estate agent. We send an email to the listing agent with all the critical rules and ask them to pass it along to the seller. Here’s the stuff we put in our email:

Please pass along the following information to the sellers so they can prepare for the radon test:

• In accordance with EPA protocol for radon testing, ALL windows and doors must be closed for 12 hours prior to the start of the test and remain closed for the duration of the test.  Normal entry and exit is, of course, fine. If the windows are open when we arrive to set the test, we will close them and begin the test; however, the test time will need to be extended by one day. Extending the radon test period may require a revision to the purchase agreement.
• Air conditioning and heating systems can be operated as normal and set between 65-80 degrees Fahrenheit for the duration of the test. If there are window or wall air conditioners present, they should be operated only in the ‘re-circulate’ mode.
• Wood-burning fireplaces will adversely affect the test and should not be operated.
• Please avoid excessive use of clothes dryers, bathroom fans, and kitchen exhaust.
• If an air exchanger is installed, set it to the lowest setting for any season for the duration of the test.  Check to make sure the filters and intake grill are clean; dirty intakes can adversely affect radon tests.

We will leave a Radon Test Notification form on the kitchen counter, which repeats this information.  Please ask the sellers or occupants to sign this form to confirm that these protocols were followed. Also, attached to this email is a PDF document from the EPA: Buyer’s and Seller’s Guide to Radon.

Again, close the windows.

The most common rule that gets violated is the windows being open. Yes, just ONE window open just a little bit on the second floor will invalidate a radon test.

We end up making a lot of extra trips to properties in the spring because people are anxious to open their windows after the deep freeze we experience all winter long. If we arrive at a home to set the test and the windows are open, we can close them and set an electronic delay on our test to start 12 hours after the set time. This will add one day to the test time.

But when we arrive at a home to pick up a radon test and find even a single window open… just a little… the entire test is invalid.

At that point, we need to get on the phone. Do we restart the test? In most cases, this will require extending the inspection contingency period. Is the buyer cool with this? What about the seller? Is the seller going to follow the rules… this time? There are a lot of questions that need to be answered right on the spot, and when everything doesn’t go exactly as planned, emotions run high, and tempers flare. It’s an unfortunate situation for everyone involved… not to mention us getting caught in the middle.

So if you’re selling your house, please read the rules for radon testing, and please follow them. Pretty please, with sugar on top.

Related link: Full rules for Radon Testing