Carroll County
Carroll County is classified by the EPA’s 1993 Map of Radon Zones as Zone 1, the highest risk category. The predicted average indoor radon screening level for this area exceeds 4 pCi/L — the EPA's recommended action level. This classification is based on geology, soil characteristics, indoor radon measurements, and building construction factors. The EPA strongly recommends that all homes in Zone 1 areas be tested for radon.
Free Radon Test Kit for New Hampshire Homes
The New Hampshire Radon Program mails free air test kits to residents. Request one at aelabs.com/nh, or call the program at (603) 271-1708 (radon@dhhs.nh.gov). Start there before buying a kit.
Measured in New Hampshire Homes
The EPA zone above comes from a 1993 map that predicts a screening level; it is not a measured average. New Hampshire’s own data tell a different story: of 32,747 home air samples tested from 2007 to 2021, about 37% were at or above 4 pCi/L, and the state estimates the average indoor level at 5.9 pCi/L (the national average is 1.3). Results above 100 pCi/L have been reported in every county.
Carroll County is one of the three New Hampshire counties (with Rockingham and Strafford) with the highest share of tested homes at or above 4 pCi/L.
These samples come from homeowners who chose to test, so they are not a random survey — but they are actual measurements. The only way to know your home’s level is to test it.
Private wells
Radon also comes from deep private wells. NH DHHS and the Department of Environmental Services recommend treating well water at or above 10,000 pCi/L (alongside air mitigation), and say treatment may be advisable between 2,000 and 10,000 pCi/L if the home’s air is at or above 4 pCi/L. Water aeration systems cost about $4,000–$6,000; air mitigation systems $1,000–$3,000.
Buying a home
Under RSA 477:4-a, a seller must give the buyer a written radon notice, which the buyer signs, before a purchase and sale agreement. The law requires notice, not a test — so ask for one.
Source: NH Department of Health and Human Services, Radon Risk in New Hampshire data brief (August 2023).
Carroll County is one of 1 counties in New Hampshire classified as Zone 1, the EPA's highest radon risk category. That means 10% of the state's 10 counties share this classification. Homes in Carroll County have predicted average indoor radon screening levels above 4 pCi/L, the EPA's recommended action level for mitigation. If you're living in, buying, or building a home in Carroll County, radon testing should be a priority.
Test for radon in Carroll County
EPA Zone 1 means predicted indoor levels above 4 pCi/L. The EPA recommends every Zone 1 home test — and mitigate if results confirm elevated levels.
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What This Means for Carroll County
Should You Test?
Yes. The EPA strongly recommends testing in Zone 1 areas. Homes here have the highest probability of exceeding the 4 pCi/L action level. Start with a short-term test kit ($15–$30 at hardware stores or online). If results are above 4 pCi/L, follow up with a second test or hire a certified professional.
Real Estate
New Hampshire law (RSA 477:4-a) requires the seller to give you a written radon notice before a purchase and sale agreement — a notice, not a test. Ask for a radon test in the home inspection; if air is at or above 4 pCi/L, mitigation typically costs $1,000–$3,000 (NH DHHS). On a private well, test the water too.
New Construction
The EPA recommends that new homes in Zone 1 be built with radon-resistant features (RRNC). These include a gas-permeable layer beneath the slab, plastic sheeting, sealed foundation cracks, a vent pipe from the gravel layer to the roof, and an electrical junction box for a future fan. Adding these during construction costs $350–$500 and is far cheaper than retrofitting later.