New Hampshire Radon Levels

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, Rockingham and Strafford counties have the highest share of tested homes at or above 4 pCi/L. Two of those three are EPA Zone 2 (“Moderate”) — the 1993 zone understates what New Hampshire homes actually measure.

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).