How do I test for radon in my basement to make sure the levels are safe?

Test the lowest livable level of your home with a short-term radon test kit, run it for at least 48 hours with windows and doors closed, then read the result in picocuries per liter (pCi/L). The EPA sets the action level at 4.0 pCi/L. At or above that number, fix it. Between 2.0 and 4.0, the EPA says consider fixing it (epa.gov/radon).

That is the short version. Here is what it looks like in a real basement.

Why test in the first place

You cannot see, smell, or taste radon. It is a radioactive gas that seeps up out of the ground through soil, rock, and the gaps in your foundation. New Hampshire and Maine sit on a lot of granite, and granite is a big radon source. So our region runs high. That is why we test.

The basement matters most because radon enters from below. The lower you go, the higher the reading tends to be. Test where the gas comes in.

The two ways to test

Short-term test. A small kit (charcoal canister or an electret/alpha-track device) sits in your basement for 2 to 7 days. You close up the house, let it run, then mail it to a lab. Quick and cheap. Good for a first look or a real estate deadline.

Long-term test. Same idea, but it runs for 90 days or more. Radon swings with seasons and weather, so a long-term test gives you a truer yearly average. If your short-term number lands in that 2 to 4 range, a long-term test tells you what your house really does over time.

You can buy a kit at most hardware stores or order one through your state program. Set it on a table or shelf in the lowest lived-in level, away from drafts, exterior walls, and the sump. Note your start and stop times. Follow the lab’s mailing instructions, because a delay can throw off the read.

How to read the result

The lab sends back a number in pCi/L. Plain rules from the EPA:

• 4.0 or higher. Take action. Put in a mitigation system.
• 2.0 to 4.0. Consider fixing it. A long-term test or a system both make sense here.
• Under 2.0. You are in good shape. Retest every couple of years and after any major foundation work.

You do not need a pro to run a basic test. A DIY kit done right is solid for a screening read. We will say that plainly. If you want a documented measurement for a home sale, that is when a certified measurement makes sense.

Where 603 fits

We can run a measured radon test for you for $50, credited toward the job if you move ahead. Our radon guy, Branden (the crew calls him “B-Radon”), is who handles it. 603 holds a state radon cert (RMS-113966), so the read is documented and defensible.

If the number comes back high, we install the fix. For a standard basement that is an active sub-slab system, a sealed pipe and fan that pull the gas out from under your slab and vent it above the roofline. For a dirt or fieldstone crawl space, we use sub-membrane depressurization, which pulls the gas from under a sealed floor barrier. A radon mitigation system runs $900 to $6,000, and most homes land around $1,950 to $2,250, and it carries a 10-year warranty on the system. The retest after install is yours to run, and that is normal. It confirms the system did its job.

One thing we will not do is talk you into a system you do not need yet. A low reading means test again later, not buy now. See /radon-mitigation/ for how the install works and /the-603-guarantee/ for what we stand behind.

If you are already opening up the basement, it is a smart time to think about water too. Radon and water both come from the same disturbed backfill soil around your foundation, and a wet basement is its own problem. See /basement-waterproofing/ and the /crawl-space-services/ page.

For state-specific guidance, NH DHHS runs a radon program, and the EPA’s radon pages walk you through testing step by step (epa.gov/radon, [verify deep URL]; NH DHHS radon program, [verify deep URL]).

Want us to handle the testing and read the result with you? Call 603-610-1770 or book your free inspection and we will get you a quote within 24 hours.

Related questions

What is a safe radon level? The EPA action level is 4.0 pCi/L. At or above that, fix it. Between 2.0 and 4.0, consider fixing it. There is no level that is officially “zero risk,” so lower is always better (epa.gov/radon).

Can I test for radon myself? Yes. A DIY short-term kit, run for 48 hours or more with the house closed up, gives a reliable screening number. For a home sale or a documented result, a certified test like ours for $50, credited toward the job if you move ahead is the way to go.

How long does a radon test take? A short-term test runs 2 to 7 days. A long-term test runs 90 days or more and gives a truer yearly average, which is the better call if your first read sits in the 2 to 4 range.

Does radon mitigation come with a guarantee? Our radon mitigation carries a 10-year warranty on the system. We do not guarantee a specific radon level unless that is written into your agreement, because the retest is run by you after the install.