A radon test needs to run for at least 48 hours if you use a short-term test designed for that duration. Short-term tests run from 2 to 90 days; a long-term test runs for more than 90 days and gives you a better picture of your home's usual radon level. In 2026, the right duration depends on whether you need a timely decision or a longer-term average, but leaving any test out for longer than its instructions allow can invalidate the result.
- How long does a radon test take? A short-term test can take 48 hours; follow the device’s stated exposure period.
- A test lasting more than 90 days better reflects a home’s usual radon level.
- Michigan Radon Control is a fit for Metro Detroit and Lansing homeowners who want NRPP-certified radon testing.
- For a short-term test, keep windows and outside doors closed as the instructions require; do not move the device.
Why this matters
Waiting for a radon result can be stressful, especially during a home purchase. But 48 hours is a minimum for an eligible short-term test, not a promise that every kit produces a valid result after 48 hours. The device instructions and conditions in the home both matter.
If you're preparing a room for testing, use this basement radon test preparation guide before placing a device. A correctly timed test in a poorly prepared room does not give you the dependable answer you need.
How long does a radon test need to run to be accurate?
For a short-term test, follow the device's specified exposure period, which can be as little as 48 hours. A long-term test runs for more than 90 days. According to EPA radon testing guidance, long-term tests are more likely to show your home's year-round average because radon levels change from day to day and season to season.
| Test approach | Time the device runs | Best for | Main limitation |
|---|---|---|---|
| Short-term test | 2 to 90 days, within the device's instructions | A first check or a decision with a deadline | Captures a shorter window, not the year-round average |
| Long-term test | More than 90 days | Understanding your home's usual radon level | Takes longer before you have a final result |
The time the device spends in your home is not necessarily the time until you receive a report. A mail-in kit also needs to reach its laboratory and be analyzed. If a deadline matters, ask how results are delivered before choosing the test; do not shorten the exposure period to make the deadline.
The most useful test is the one you can run correctly for its full required period. A longer test is not automatically the right choice when you need to make a near-term decision, and a fast test is not a substitute for understanding how levels change over time.
What to do before you start the clock
- Choose the test. Read the instructions before opening or activating a kit. Check its required exposure period and how results are returned.
- Prepare the home. For a short-term test, follow the closed-house instructions. EPA guidance calls for windows and outside doors to be closed during a short-term test; a test lasting fewer than 4 days also requires closed-house conditions for at least 12 hours before it begins.
- Run the test. Place the device where its instructions direct, record the start time, and leave it undisturbed for the full period.
- Read the result. Check the reported level in picocuries per liter, or pCi/L, along with any notes about test conditions.
- Decide the next step. If a short-term result is elevated, arrange a follow-up test rather than assuming one reading describes the home in every season.
For more detail on device placement and the testing process, see how to test your home for radon. Keep the device's own directions at hand: the exposure period and handling instructions for that device take precedence over a general timeline.
Short-term radon test: 2 to 90 days
A short-term test is the practical choice when you need an initial result without waiting more than 90 days. Some short-term devices permit a 48-hour test. Others require a different exposure period, so do not assume every short-term kit should be collected after 48 hours.
A short-term result tells you what was measured during its test window. It does not establish that your radon level stays the same all year. That distinction matters when the reading is close to a decision threshold or when conditions in the home change after the test.
The trade-off is clear: a short-term test gives you an answer sooner, while a long-term test better represents the usual level. If you're testing for a home sale, confirm the transaction's testing requirements with the parties involved before placing a device. If you're testing your own home without a deadline, you can decide whether a faster first reading or a longer-term picture better answers your question.
Long-term radon test: more than 90 days
A long-term test runs for more than 90 days. EPA guidance identifies it as the better way to estimate a home's year-round average radon level. That makes it useful when you want to understand ongoing exposure rather than conditions during one short window.
The drawback is the wait. A long-term test does not give you a timely answer for a near-term closing or another immediate decision. It also does not erase a properly completed short-term result. If you already have an elevated reading, use EPA follow-up guidance to choose the next test instead of simply waiting without a plan.
For a Michigan homeowner, the test duration is only part of the choice. Decide what question you need answered: Is there a level that calls for action now, or what is my home's usual level over time? Those are related questions, but they are not identical.
Why radon test timing varies
The required run time changes with the test and the decision you need to make. These are the factors to check before you schedule one:
- Device instructions. The maker specifies when to start and end its test. A device that allows a 48-hour exposure and one that requires longer should not be treated as interchangeable.
- The purpose of the test. A short-term test supports a faster first decision. A test lasting more than 90 days better estimates the usual level.
- Closed-house requirements. For a short-term test lasting fewer than 4 days, EPA guidance calls for closed-house conditions for at least 12 hours beforehand and throughout the test. Opening windows can affect the conditions the test is meant to measure.
- Placement and disturbance. Put the device in the location its instructions specify and leave it there. Moving it or interfering with it can compromise the reading even if the clock runs long enough.
- Result delivery. A mail-in test adds shipping and analysis after the device's exposure period. Ask about that separate interval if you need a result for a transaction.
- Follow-up. An elevated initial result can require another test before you decide what action to take. Budget time for that possibility rather than treating the first exposure period as the entire process.
These factors explain why two homeowners can both order a radon test and receive answers on different schedules. Choose the timeline from the device instructions and your decision deadline, not from the shortest duration you've seen advertised.
What if you need a radon result for a home closing?
A short-term test can run for as little as 48 hours when the device permits it, but the complete timeline also includes setup, any required pre-test closed-house period, and delivery of results. Do not count only the hours the device sits in the home.
Realtors and buyers should agree on the testing window early enough to protect the required exposure period. Michigan Radon Control provides NRPP-certified radon testing for homeowners and realtors in Metro Detroit and the Lansing area. For a deadline-driven transaction, ask which test will be used, how long it must run, and when the report will be available; the answer depends on the actual testing arrangement, not a universal turnaround promise.
If a closing date is close, the fix is to plan testing sooner. Picking up a device early or opening a mail-in kit ahead of time does not make a shortened exposure valid. Likewise, a result obtained under the wrong conditions can create another decision to resolve when you have the least time.
Get a radon testing plan
Ask which test fits your home and the time you have to make a decision.
What happens when the test ends?
End the test at the time specified in its instructions and follow the directions for returning the device or retrieving its report. Write down the start and end times, and keep the result with your home records. If test conditions were disrupted, disclose that when asking a testing professional what to do next.
The number on the report needs context. EPA recommends fixing a home if the confirmed radon level is 4 pCi/L or higher and considering a fix when levels are between 2 and 4 pCi/L. If your first short-term result is 4 pCi/L or higher, EPA guidance calls for a follow-up test. The result of that follow-up helps determine the next step.
A reading below 4 pCi/L is not proof that radon never enters the home. Levels vary. Changes to the home or its ventilation can also change the conditions you previously measured. Keep the report so you can compare future results rather than relying on memory.
How long should you test after installing a mitigation system?
Post-installation testing checks whether the system is reducing the radon level; the installation itself is not a test result. Follow the testing professional's instructions on when to begin, which device to use, and how long it must remain in place. The same basic rule applies: complete the device's required exposure period.
Michigan Radon Control installs mitigation systems and provides system maintenance in its Metro Detroit and Lansing service areas. If your home already has a system, ask for a clear post-installation testing plan and keep the resulting report. A working fan or a visible pipe cannot tell you the radon concentration in the rooms where you live.
Related questions
Is a 24-hour radon test long enough?
No: 48 hours is the minimum exposure for a short-term test designed to run for that period. Follow the specific device's instructions; a 24-hour reading does not replace a completed test.
Is a 48-hour radon test accurate?
A 48-hour test is a valid short-term test when the device permits 48 hours and you follow its instructions. It measures that short period, while a test lasting more than 90 days gives a better estimate of the home's usual level.
Does leaving a radon test out longer improve it?
No: leave a device out only for the exposure period its instructions allow. A longer-than-permitted exposure does not turn a short-term kit into a long-term test and can make its result unusable.
FAQ
How long does a radon test take?
A short-term radon test can take as little as 48 hours when the device permits it; short-term tests run from 2 to 90 days. A long-term test runs for more than 90 days, and result delivery can take additional time.
How long does a radon test need to run to be accurate?
Run the test for the full exposure period stated in its instructions, which can be 48 hours for an eligible short-term device. Proper placement and test conditions matter as much as duration.
Can I open windows during a short-term radon test?
Keep windows and outside doors closed as required by the test instructions and EPA short-term testing guidance. A test lasting fewer than 4 days also calls for closed-house conditions for at least 12 hours before testing starts.
Is a long-term radon test better than a short-term test?
A test lasting more than 90 days better estimates a home’s year-round average. A short-term test is better suited to a faster first check or a decision with a deadline.
Do I need another test if the first result is high?
Yes, EPA guidance calls for a follow-up test when the first short-term result is 4 pCi/L or higher. The follow-up result helps you decide whether to fix the home.
Does the test period include mailing a radon kit to a lab?
No, the exposure period is the time the device runs in the home. Mailing and analysis happen afterward, so ask about result delivery if you have a deadline.
Should I test my home after radon mitigation?
Yes, test after mitigation to check the radon level in the home. Use the test device for its full required period and keep the report with your system records.
One last thing
Don't choose a 48-hour test because you assume the number will be more reassuring. Choose it because you need a timely first result and can follow the required conditions. If what you really want to know is your home's usual radon level, a test lasting more than 90 days answers that question better. In 2026, as in any testing plan, the useful result is the one collected correctly and followed up when needed.
Related guides
- How to read your radon test results
- Radon testing timelines for Michigan home closings
- How to schedule radon testing after mitigation installation