Does it matter if I test for radon in the summer or the winter

Yes, the season matters. Radon usually reads higher in winter, so a winter test gives you the more telling number. But the season is not a reason to skip testing. The right move is a long-term test that runs across both seasons, or to test in winter if you want the toughest read on your home.

Here is why winter runs high. When it is cold, your house is closed up and the heat is on. Warm air rises and leaves through the upper floors, which pulls air in low, right through the basement slab and any cracks. That pull is called the stack effect. It draws more radon up out of the soil. Summer is looser. Windows open, doors open, air moves through, and the gas has more ways to escape. Same house, two different numbers.

So a summer test can read low and still hide a winter problem. We see this with NH homes a lot. A homeowner tests in July, gets a calm number, then the slab tightens up come January and the reading climbs. The soil does not change. The house does.

What we tell people is simple. If you do a short-term test, do it in the heating season with the house closed up the way you live in it. If you want the real average, run a long-term test for 90 days or more, ideally straddling winter. Long-term is the better read because radon swings day to day with weather and pressure. One quick test is a snapshot. A long-term test is the truth over time.

The number to watch is the EPA action level of 4.0 pCi/L. At or above that, the EPA says fix it. Between 2 and 4, they say consider fixing it. New Hampshire sits over a lot of granite, so high readings are common here, and the NH DHHS radon program has guidance on testing your home. Granite gives off radon as it breaks down, and that gas finds its way through the disturbed backfill and up through the floor wall joint into your basement.

A quick word on the floor wall joint, since that is where a lot of radon and water both come in. That seam between your slab and your foundation wall is never fully sealed. Soil gas pushes through it. So does ground water. If you are already chasing a damp basement, radon is worth checking at the same visit, because the fix paths overlap.

Now the part most companies skip. You do not need us to test. A homeowner can buy a test kit, set it, and mail it off, and the radon test fee for a pro test runs $50, credited toward the job if you move ahead. Either way, do it right. House closed, test kit on the lowest lived-in level, no fans running. If the number comes back at or above 4.0, that is when a mitigation system earns its keep.

A radon system is straightforward. For a normal poured or block basement, we install an active sub-slab system, a sealed pipe and a quiet fan that pulls the gas from under your slab and vents it up and out above the roofline. For a dirt or fieldstone crawl space, the fix is sub-membrane depressurization, the same idea but pulling from under a sealed membrane over the dirt. We install both. Radon mitigation cost runs $900 to $6,000, and most homes land around $1,950 to $2,250, and the system carries a 10-year warranty. We do not put a radon-level guarantee in unless it is in writing, and retesting after the install is your job, not ours, so plan to test again once the fan is running.

Our radon guy is Branden. We call him B-Radon. He does this work day in and day out across New Hampshire, Maine, and Massachusetts, so if your number is borderline and you want a real read on what it means, ask for him.

One more thing. Do not let a clean summer test talk you out of a winter retest if something feels off. Radon does not smell. It does not show. The only way to know is to measure, and to measure when the house is buttoned up tight. That is winter, here.

If you want a hand, we will come look. We offer a free inspection and a free estimate, and you get your quote within 24 hours. Call us at 603-610-1770 or book your free inspection, and we will get Branden out to you.

Learn more about how we handle the work on our radon mitigation page, see how radon and water share a path on our basement waterproofing and crawl space services pages, and read what we stand behind on the 603 guarantee. For the testing science, the EPA radon program and NH DHHS radon are the places to start.

Related questions

How long does a radon test take? A short-term test runs 2 to 7 days with the house closed up. A long-term test runs 90 days or more and gives a truer yearly average. Long-term is the better read because radon swings with weather. The radon test fee for a pro test runs $50, credited toward the job if you move ahead.

What radon level is too high? The EPA action level is 4.0 pCi/L. At or above that, fix it. Between 2 and 4, the EPA says consider fixing it. There is no level that is fully zero, so the goal is to get it as low as you reasonably can.

Do I need to retest after a radon system goes in? Yes, and that part is on you. We do not retest for you after the install. Once the fan is running, set a new test on the lowest lived-in level to confirm the number dropped. Our systems carry a 10-year warranty.

Does radon come in the same way as water? Often, yes. Both push up through the floor wall joint, that seam between your slab and your wall, and through cracks in disturbed backfill. If you are fixing a wet basement, it is worth testing radon at the same time.