A professional radon test takes a minimum of 48 hours under closed-house conditions. From device placement to receiving your results, plan on three to five days total.
Whether you are buying a home in Atlanta or have lived in your house for years without testing, here is a full breakdown of how radon testing actually works, the difference between test types, and what your results mean once they come back.
What Is Radon and Why Do You Need to Test for It?
Radon is a radioactive gas that forms naturally as uranium in soil and rock breaks down.
It seeps up through the ground and into buildings through foundation cracks, joints, and other openings. Once inside, it gets trapped and builds up over time.
The problem is that radon is completely invisible, odorless, and tasteless. The only way to know if your home has elevated levels is to test for it. According to the EPA’s radon guidance, radon is the second leading cause of lung cancer in the United States, responsible for more than 21,000 deaths each year.
Georgia homeowners have more reason than most to pay attention. The state’s geology, especially in the north Georgia mountains and the upper Piedmont region around Metro Atlanta, includes granite and gneiss bedrock that contains higher concentrations of uranium.
Gwinnett County and Cobb County both fall into EPA Zone 1, meaning homes there have the highest predicted potential to exceed the 4.0 pCi/L action level. Even counties in Zone 2, which covers much of Metro Atlanta, see between 25 and 40% of tested homes exceed that threshold.
Radon levels vary house by house. Your neighbor testing low is no guarantee your home will too. Testing is the only way to know.
How Does a Professional Radon Test Work?
A professional radon test is a controlled measurement process, not just dropping a device in the basement. Here is what each step involves.
Step 1: Device Placement
The inspector places a testing device at the lowest livable level of the home. That could be a finished basement, a first-floor bedroom, or a crawl space area, depending on the home layout. The device goes at least 20 inches off the floor, away from exterior walls, drafts, humidity sources, and HVAC returns.
For professional tests, most inspectors use Continuous Radon Monitors (CRMs). These electronic devices record hourly readings throughout the test period, which means they can detect any interference or unusual spikes.
At Avalon, we use the Corentium Pro, an AARST-NRPP and NRSB-certified device that uses alpha spectrometry to calculate radon concentration accurately.
Step 2: Closed-House Conditions
Before and during the test, the home needs to maintain closed-house conditions. That means:
- All exterior windows and doors remain closed (except for normal entry and exit)
- No fans or machines that bring in outside air
- HVAC runs normally in auto mode
- No whole-house fans or attic ventilation during the test period
Closed-house conditions must be in place for at least 12 hours before the test starts and continue for the full duration. Violating these conditions can invalidate the test in some states and will definitely produce inaccurate results.
Step 3: Data Collection
Once the device is placed and conditions are met, the test runs. For most professional short-term tests used in real estate transactions, the minimum sampling period is 48 hours. Some inspectors run tests up to 96 hours for additional confidence in the data.
During this period, you go about your normal routine. Normal comings and goings through doors are fine. You just cannot open windows, run whole-house fans, or move or tamper with the device.
Step 4: Retrieval and Results
After the sampling period ends, the inspector retrieves the device and pulls the data. With a Continuous Radon Monitor, results are available the same day it is picked up. There is no lab shipping involved.
You typically receive your written report within 24 hours of retrieval.
Charcoal canister tests (often used in DIY kits) have to be mailed to a lab after the exposure period ends, which adds several days to the timeline.
Short Term vs Long Term Radon Test
The type of test you need depends on your situation.
| Test Type | Duration | Best Use |
| Short-term | 2–7 days (48 hrs minimum) | Real estate transactions, initial screening |
| Long-term | 90 days to 1 year | Ongoing exposure monitoring, seasonal accuracy |
Short-term tests are the standard for real estate transactions. They are designed to measure the radon potential of a home under controlled conditions, not your actual day-to-day exposure. They give buyers and sellers a fast, reliable snapshot during the inspection period.
Long-term tests use alpha track detectors that sit in the home for months, capturing radon levels across seasons and varying home conditions. Radon levels fluctuate with weather, temperature, and how the home is ventilated. A long-term test smooths out those swings and gives the most accurate picture of average exposure over time.
If your short-term test comes back close to the 4.0 pCi/L action level (say, between 2 and 4), a long-term follow-up is a smart next step before deciding on mitigation.
What Affects How Long a Radon Test Takes?
The 48-hour minimum is fixed, but a few factors can stretch the overall timeline.
- Device type: Continuous monitors produce on-site results the day of retrieval. Charcoal canisters need lab processing, which adds 1–3 days depending on the mail turnaround.
- Test validity issues: If closed-house conditions were not maintained properly, or if the device was tampered with, the test may need to be rerun. Always confirm with your inspector what conditions are required before the device goes down.
- Scheduling during a closing: If you are buying a home and ordering radon testing as part of your inspection contingency, get it scheduled as early as possible. The test needs to run, the inspector needs to retrieve it, and you need time to negotiate repairs if levels come back elevated. A test placed on day one of your inspection window gives you the most flexibility.
- Weather: Significant storms or rapid temperature swings can influence radon readings. Most inspectors will note these conditions in the report and may recommend extending the test for additional data.
What Do Radon Test Results Mean?
Radon is measured in picocuries per liter, written as pCi/L. Here is what the numbers mean:
| Level | What It Means |
| Below 2 pCi/L | Low: within normal range for most homes |
| 2–4 pCi/L | Moderate: EPA recommends considering mitigation |
| 4 pCi/L or higher | Elevated: EPA recommends fixing the home |
The national average indoor radon level is about 1.3 pCi/L. If your result comes back at or above 4 pCi/L, the EPA recommends having a radon mitigation system installed. A licensed radon mitigator installs a vent pipe and fan system that draws radon out from under the foundation before it can accumulate inside.
If your result is between 2 and 4 pCi/L, mitigation is worth considering, especially if you spend a lot of time in the lower level of the home or are planning to convert a basement into a bedroom or office.
Learn more about what radon levels mean for your home and whether every home needs to be tested, regardless of whether it has a basement.
For real estate transactions, if the test comes back elevated, the buyer can negotiate with the seller to have mitigation installed before closing. This is a common outcome and does not have to kill the deal.
Related Questions to Explore
How long does a radon test take for a home purchase? For a real estate transaction, a professional short-term radon test runs a minimum of 48 hours under closed-house conditions. Once the inspector retrieves the device, results are typically available within 24 hours, especially with a Continuous Radon Monitor.
Plan on three to five days from placement to results. Schedule the test at the start of your inspection contingency period, so you have time to negotiate if levels come back high.
Can I do a radon test myself, or do I need a professional? You can purchase short-term charcoal canister test kits at most hardware stores. The EPA recommends using a professional if you are buying or selling a home. Professional tests use more accurate equipment, are placed correctly for the home layout, and produce certified reports that satisfy lenders and real estate transactions.
DIY kits may not be accepted for real estate purposes, and they lack the tamper-detection and hourly logging that continuous monitors provide.
What happens if my radon test comes back high? A result at or above 4 pCi/L means the EPA recommends fixing the home. Contact a certified radon mitigation contractor. The most common fix is a sub-slab depressurization system, which installs a vent pipe through the foundation and a fan to redirect radon gas outside before it builds up indoors.
Mitigation is effective, and most homes can be reduced to below 2 pCi/L. If you are buying a home, a high radon result is a negotiating point, not necessarily a deal-breaker.
When to Call a Professional for Radon Testing
If you are in any of these situations, a professional test is the right call rather than a DIY kit:
- Buying or selling a home: Professional tests produce certified reports required by most lenders and real estate agents. DIY kits may not satisfy these requirements.
- It has been more than two years since your last test: Radon levels shift over time, especially after home renovations, foundation changes, or significant weather events.
- You are finishing a basement or converting a lower-level space into a living area: Spending more time at a lower level increases your exposure. Test before you start and after the work is done.
- You live in north Georgia or Metro Atlanta: Gwinnett, Cobb, and surrounding counties fall in EPA Zone 1 or Zone 2, where elevated radon is more common.
- A previous test came back between 2 and 4 pCi/L: A professional long-term test gives you a more accurate baseline to decide on mitigation.
At Avalon, our radon testing service in Atlanta uses AARST-NRPP-certified continuous monitors, so you get same-day results once the 48-hour sampling period ends. We serve Metro Atlanta and the surrounding Georgia counties.
Schedule your radon test and get your results within the week.
Conclusion
A radon test works by placing a certified monitor at the lowest livable level of your home and letting it measure radon concentration for at least 48 hours under closed-house conditions. From start to finish, plan on three to five days.
Short-term tests are the standard for real estate transactions. Long-term tests give the most accurate picture of ongoing exposure. Results come back the same day with a continuous monitor.
Key takeaways:
- The minimum sampling period for a valid short-term test is 48 hours
- Closed-house conditions must be in place 12 hours before the test starts and throughout
- The EPA action level is 4 pCi/L: at that point, mitigation is recommended
- Georgia homeowners, especially in Metro Atlanta, face above-average radon risk due to local geology
Ready to get your home tested? Avalon’s certified inspectors serve Metro Atlanta and the surrounding Georgia area. Get in touch for a free quote today.
