Why Summer Is the Best Time to Test for Radon (and Fix It)

Most homeowners assume radon is a winter problem. After all, it sounds like the kind of invisible danger that lurks in cold, sealed-up basements during the dark months of the year. So when summer arrives and you crack the windows to let in the breeze, it's tempting to put radon testing on the back burner.

Here's the truth: radon doesn't take a summer vacation — and if you have central air conditioning, summer may actually be the *best* time of year to test and fix it.

Closed-House Conditions = Accurate Readings

The EPA requires closed-house conditions for short-term radon tests: all doors and windows closed for at least 12 hours before testing and throughout the test period. This is exactly what happens in summer when the AC is running.

In summer, families run air conditioning around the clock. Doors stay shut. Windows stay sealed. Your house becomes the airtight testing environment the EPA specifies — naturally, without any behavior change required.

Compare that to spring and fall, when windows are open half the day, temperatures swing, and neighbors are airing out their homes. Those conditions can dramatically undercount radon levels, giving you a false sense of security.

Radon Doesn't Drop to Zero in Summer

Here's what many homeowners do not realize: radon levels do not drop to zero in summer. They typically run 20–40% lower than peak winter levels in most regions — but in well-sealed, air-conditioned homes, the difference is smaller than you might expect.

• The EPA action level is 4 pCi/L. A home testing at 3 pCi/L in summer may be well above 4 in winter with more air exchange.
• In high-risk states like Iowa, Minnesota, Pennsylvania, and Ohio, average indoor radon levels are 6–10+ pCi/L year-round.
• Approximately 1 in 15 U.S. homes has radon at or above the EPA action level — and most of those homeowners have never tested.

Testing in summer gives you a realistic floor. If your summer test comes back elevated, you almost certainly have a year-round problem.

Summer Is Ideal for Mitigation Installation

If your test comes back elevated (the EPA action level is 4 pCi/L), summer is arguably the best season to get the fix done:

• Mitigators have more scheduling flexibility. Demand spikes in late fall and winter when homeowners panic after testing during the heating season. Summer bookings are often easier to land.
• Crews work comfortably. Installing a sub-slab depressurization system involves drilling through your foundation and routing PVC piping to the exterior. It's easier work in dry, warm weather.
• You see results before winter. Getting your system installed in July means you go into the heating season — when radon risk tends to peak — already protected.

Radon mitigation cost runs $800–$2,500 for most slab and basement homes. Summer jobs tend to run quicker with fewer weather-related complications.

The Back-to-School Home Inspection Window

If you are buying or selling a home, summer radon testing slots into a natural inspection cycle. The annual surge in home sales peaks in spring and early summer, and radon tests are now standard in real estate transactions in most of the country.

For buyers: a radon contingency in your offer is common and sensible. A 48–72 hour short-term test during the inspection window gives you enough data to negotiate mitigation costs before closing.

When to Test: A Simple Framework

• Test now if: you have never tested, your home is 15+ years old, you have done recent renovations, or you have added living space in the basement.
• Test again if: your last test was more than 2 years ago, or you had results between 2–4 pCi/L.
• Mitigate immediately if: any test comes back at or above 4 pCi/L.

A long-term test (90 days or more) is the gold standard. But a short-term summer test in a closed, air-conditioned home is a solid starting point.

Certification Matters

Before hiring anyone to test or mitigate your home, confirm they hold active certification from NRPP (National Radon Proficiency Program) or NRSB (National Radon Safety Board). An uncertified contractor may install a system that doesn't reduce radon to safe levels.

Find a certified radon mitigator near you →

Radon testing kits run $15–$30 at most hardware stores or online. For a hazard that causes 21,000 deaths a year, it is the cheapest home safety check you will ever do.