Why Radon Peaks in Winter?

Three factors converge in Illinois winters to drive indoor radon concentrations to their annual highs:

1. Closed-building effect: When outdoor temperatures drop below freezing, windows and doors stay shut for months. Without natural ventilation, radon that seeps into the home has nowhere to go and accumulates steadily.

2. Stack effect: Warm indoor air rises and exits through upper portions of the building. This creates a slight negative pressure at the foundation level — essentially turning the house into a pump that draws soil gas (and radon) in from below.

3. Frozen ground: When the soil above the frost line is frozen, radon that would normally escape vertically through soil is forced horizontally toward building foundations instead.