Blog › 2026-10-21
How to Test Your Greenville Home for Radon
Radon testing is one of the easiest home projects you'll ever do. The hard part is doing it correctly, because a few small mistakes can skew the number. This guide walks through it for a typical Upstate house, whether it sits on a basement, a slab or a crawlspace.
Step 1: Choose your test type
| Option | How long | Best for |
|---|---|---|
| Short-term DIY kit (charcoal, etc.) | 2 to 90 days (most kits 2 to 7 days) | A first screen at low cost |
| Long-term DIY test (alpha-track, etc.) | More than 90 days | Your year-round average |
| Professional continuous radon monitor | Usually at least 48 hours | Home sales, follow-ups, hour-by-hour data |
EPA notes that a long-term test gives a better picture of your year-round average, because radon rises and falls with weather and season. A short-term test is a fast snapshot. Many homeowners start short-term and follow up if the result is near or above the action level.
Step 2: Pick the right spot
- Lowest level of the home that is lived in, or could be (a finished basement counts; a crawlspace doesn't).
- At least 20 inches off the floor, in the breathing zone.
- Away from exterior walls, windows, doors, vents and fans.
- Not in a kitchen, bathroom or laundry room, where humidity and exhaust fans interfere.
- Not next to a sump pit or floor drain.
- Somewhere it won't be bumped or moved by kids or pets.
Split-level and slab homes, common across Simpsonville and Mauldin subdivisions, often put the lowest living area on the ground floor. That's where the test goes.
Step 3: Set up "closed-house conditions"
For short-term tests under four days, EPA guidance is to keep windows and exterior doors closed (normal entry and exit is fine) for at least 12 hours before the test and throughout it. Run your heat or air conditioning normally, but don't use whole-house fans or window fans that pull in outside air. Avoid testing during severe storms or unusually high winds, which can change indoor radon temporarily.
Greenville summers make this easy, since most homes are closed up with the AC running anyway. In spring and fall, when people like to open windows, plan your test window ahead of time.
Step 4: Run the test and mail it promptly
Write down the start date and time. When the test period ends, seal the kit exactly as the instructions say and mail it to the lab right away. Delays in the mail can affect charcoal-based results. Professional monitors skip this step: the tester retrieves the device and gives you a report.
Step 5: Read your result
- 4 pCi/L or higher: EPA's action level. Do a follow-up test to confirm (a second short-term or a long-term test). If the average confirms it, plan to install a radon mitigation system.
- 2 to 3.9 pCi/L: EPA suggests considering a fix. There's no known safe level.
- Below 2 pCi/L: Good news. Retest every couple of years, and after big renovations, a new HVAC system, or finishing a basement.
Common mistakes we see
- Testing in the crawlspace or garage instead of the living space.
- Opening windows mid-test on a nice day.
- Letting a kit sit for weeks before mailing it.
- Assuming a neighbor's low result applies to your house.
- Testing once, years ago, and never again after remodeling.
Why Greenville homes especially should test
Greenville County is the only South Carolina county in EPA Radon Zone 1 (see Is radon a problem in Greenville County?). That's a county-level prediction, not a verdict on your home, which is exactly why a test matters.
Want it done for you?
Our Greenville radon testing uses a continuous monitor and comes with a plain-English explanation of your result. Buying or selling? Read radon tests in Greenville real estate deals.
Reference: EPA, A Citizen's Guide to Radon.
Quick answers
Where should I put a radon test kit?
In the lowest lived-in level of the home, at least 20 inches off the floor, away from drafts, exterior walls, kitchens, bathrooms and sump pits.
How long should a radon test run?
Short-term tests run 2 to 90 days and long-term tests more than 90 days. Professional real-estate tests usually run at least 48 hours.