Why Do Radon Levels Change?

Radon levels inside a home are never constant. They depend on how much soil gas is being drawn into the house at any moment — and that changes with the weather, the season and how you use your heating, cooling and ventilation.

Air pressure is the driver

Radon enters through cracks and openings in the foundation when air pressure inside the house is lower than in the soil. Anything that lowers indoor pressure pulls in more soil gas.

Weather and rain

Heavy rain and snow can seal the ground surface, so soil gas looks for the easiest way out — often through your basement. Falling barometric pressure before a storm can have a similar effect.

Winter and the stack effect

In cold weather, warm air rises and leaks out of the upper floors. That draws replacement air in at the bottom of the house, including soil gas. Many homes see their highest radon levels in winter.

HVAC, fans and time of day

Exhaust fans, dryers and furnaces that pull air out of the house can increase radon entry. Levels often peak at night and early in the morning, when the house is closed up and outdoor temperatures drop.

What this means for testing

Because levels swing so much, a 2-day test is only a snapshot. A long-term test or a continuous monitor gives a far more reliable picture of your real exposure.