Manchester, New Hampshire – A dangerous gas could be building inside homes across southern New Hampshire right now as chilly spring nights keep windows closed, allowing radon—known as the “invisible killer”—to accumulate indoors within hours. The risk increases quickly when airflow is limited during sharp overnight temperature drops.
According to the U.S. Environmental Protection Agency, radon is a radioactive gas that forms naturally in soil and seeps into homes through foundation cracks, sump pumps, and crawl spaces. New Hampshire is classified as a high radon potential state, with data showing roughly 30% to 35% of homes test above the EPA action level of 4 picocuries per liter.
In Manchester and across Hillsborough County, homes with basements are especially vulnerable this time of year. Nearby communities including Nashua, Concord, and Derry often see elevated indoor readings during early spring as residents keep homes sealed overnight. State health officials warn that radon is the second leading cause of lung cancer in the U.S., linked to about 21,000 deaths each year.
Radon exposure produces no immediate symptoms, making testing the only reliable way to detect it. Short-term test kits can return results within 48 to 96 hours, and mitigation systems can reduce indoor levels by up to 99 percent.
Residents are urged to test homes now as conditions through April continue to favor indoor buildup. Additional alerts could be issued as risks persist into early summer.
