Radon & Indoor Air Testing Guide

Radon is a naturally occurring radioactive gas produced by the decay of uranium in soil and rock. It is colorless, odorless, and tasteless — you cannot detect it without testing. Radon seeps into homes through foundation cracks, gaps around pipes, sump pump openings, and any other penetration where soil contacts the building envelope. Once inside, it accumulates to levels that can significantly increase lung cancer risk with long-term exposure.

The EPA estimates that radon causes approximately 21,000 lung cancer deaths annually in the US. The DMV area has variable radon risk — some neighborhoods have naturally low levels while adjacent areas can have dangerous concentrations. Geological formations in Northern Virginia, particularly in Fairfax and Loudoun counties where granitic and metamorphic bedrock is common, produce higher radon levels than the sedimentary geology under much of DC and Prince George's County.

Your HVAC system influences radon levels in three ways. First, the air handler creates pressure differentials. When the blower runs, it pulls return air from the house, creating slight negative pressure on the lower floors. This negative pressure acts like a vacuum, drawing soil gas (including radon) through foundation cracks. Homes with return ducts in the basement and leaky basement ductwork experience the strongest depressurization effect.

Second, duct leaks in basements and crawl spaces amplify the problem. A leaky supply duct in the basement pushes conditioned air into unconditioned space. To make up for this lost air, the system pulls more air from other sources — including soil gas. We measure duct leakage during our inspections, and homes with significant basement duct leaks often have elevated radon readings.

Third, the HVAC system distributes radon throughout the home. Once radon enters the basement, the return air system picks it up and distributes it to every room in the house. Sealing duct leaks and ensuring adequate return air paths can reduce this distribution effect.