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It’s early October, and the heat is about to come on for the first time since spring. You’ll seal the windows, run the furnace, and spend the next five months inside a closed box. A radon test only means something if it measures that box, so this is the right time to plan one.
Most homeowners hear about radon in January. Here’s what to do before then, and why.
The Short Version: Winter is the best season for a short-term radon test, because a heated, closed-up home tends to give the most reliable reading.[4][6][7][11][15] January is National Radon Action Month, and the EPA and U.S. Surgeon General recommend testing every U.S. home.[3][5][14] If your result is 4 pCi/L or higher, the EPA says to fix it.[8][9][13]
Key Takeaways
- Test during the heating season. Virginia’s state guidance says indoor radon usually peaks in the coldest months.[15]
- Close the house for at least 12 hours before a short-term test starts.[4][7][10]
- At 4 pCi/L (picocuries per liter, the unit radon is measured in) or above, mitigation is the next step.[8][9][13]
- If the result is high, book early. Mitigation installers are not always free to start the week you call.
What Radon Action Month actually is
January is the month the EPA, the CDC, the American Lung Association and state health departments push radon awareness at the same time.[3][5][14] Michigan’s environment department put out its own January announcement for 2026.[8] The CDC frames it as Radon Awareness Week.[3]
The message is the same everywhere: test, and fix what you find. The EPA says testing is easy and inexpensive. Some state programs and municipalities hand out free kits.[9]
The timing is no accident. January sits in the middle of the season when homes are shut tight.
Why winter readings are the ones to trust
Radon is a gas that rises from the soil. In winter, your closed house and running heat tend to pull more of it indoors, and fewer open windows dilute it. Michigan calls the heating season the ideal time to test because of those closed-house conditions.[4][8] Massachusetts names winter as the best time and says to retest if a summer result comes back low.[6]
Here’s what most people miss. A test run with the windows open in June can read low and give you false comfort. A winter test is the more conservative reading.
Reality Check: A winter reading is a snapshot, not your average exposure over the year. Short-term tests run 2 to 7 days, though some devices run up to 90.[4] A long-term test runs at least 90 days and better reflects year-round exposure.[11] A short test is a screen. A high number is a reason to act or to confirm with a longer test, not a reason to panic.
Short-term vs. long-term: pick one
| Short-term test | Long-term test | |
|---|---|---|
| Duration | 2 to 7 days (some devices up to 90)[4] | At least 90 days[11] |
| Best for | Quick screening, home sales | Year-round average exposure[11] |
| Closed-house rule | At least 12 hours before starting, closed throughout[4][7][10] | Closed conditions for at least half the test period[7][11] |
| Best season | Heating season | Heating season, running into spring |
How to run the test correctly
State guidance agrees on the basics:
- Close up first. Keep windows and exterior doors shut for at least 12 hours before a short-term test, except for normal entry and exit.[4][7][10]
- Run the heat normally. Check the device instructions on attic, kitchen and bathroom fans.[4][7]
- Pick the right room. Use the lowest livable level, usually the basement if you use it regularly. A bedroom, living room, den or rec room works.[4][15]
- Place it well. Keep it at least 20 inches off the floor, away from exterior walls, windows, doors, fans, humidity and drafts.[4][10][15]
Pro Tip: Put the test date on your calendar next to a weather forecast. A stretch of mild weather with windows cracked open ruins the closed-house conditions you’re trying to measure. Wait for a cold week.
Region by region
The research gives specific guidance in several states:
- Michigan: The heating season is the ideal time to test.[4][8]
- Wisconsin: Winter is a good time, with the 12-hour pre-test closure.[7] If you’re in Milwaukee, see radon professionals in Milwaukee.
- Virginia: Indoor radon usually hits its maximum in the coldest months.[15]
- Massachusetts: Winter is best, and low summer results should be retested.[6]
- Oregon: Heating season is the time for long-term testing.[11]
- Nevada: Heating-season testing is recommended. Our earlier research also found post-mitigation testing is expected within 30 days of installation, and no sooner than 24 hours after the fan starts.
Testing in the Midwest or Northeast? Compare radon professionals in Chicago or in Philadelphia.
When installers get busy
I’ll be honest: the research for this piece didn’t turn up dated booking data showing exactly when installers fill up. Our earlier research on radon contractors did flag seasonal demand spikes in high-radon regions, and winter scheduling pressure on final bids. That’s consistent with a January awareness push sending homeowners to test at the same time.
So the practical move is to test in October or November. If the result is 4 pCi/L or higher, you’ll be getting quotes before the January rush. Our cost guide and state-by-state breakdown cover what to expect. Earlier research put Midwest mitigation pricing at roughly $1,000 to $2,300, with mixed foundations and winter scheduling affecting final bids.
By the Numbers
From RadonTrust directory data (see industry statistics):
- Verified providers listed: 665 across 47 states
- Most providers: Illinois (102), Colorado (70), Ohio (43)
- NRPP certified radon measurement professional: 43 (6%)
- NRPP certified radon mitigation professional: 27 (4%)
- NRPP Certified: 17 (3%)
- Average years in business (where published): 27.1
Measurement and mitigation are separate credentials. Our guide to measurement vs. mitigation services explains whether you need both.
Practical Bottom Line
- Buy or book a test this month. The EPA and Surgeon General recommend every home be tested.[5][9]
- Test once the heat is running. Close the house 12 hours before and place the device 20 inches or more off the floor.[4][10]
- At 4 pCi/L or above, fix it.[8][9][13] Ask about NRPP or NRSB credentials using our 15 questions to ask.
- Plan the retest. The Lung Association says every 5 years without a system and every 2 with one.[1][8]
New to all of this? Start with the complete guide to radon mitigation contractors.
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Nick built RadonTrust because the radon industry still mixes measurement and mitigation in ways that create conflict of interest — the same pro who tells you your level is high often wants to sell you the fix. This directory surfaces independent, credentialed professionals first.
