Why Do Radon Levels Fluctuate?


We test homes for radon weekly. In every test, we record spiking levels of radon. In the photograph above you will notice the fluctuation of recorded levels go from a high of 13.0 pCi/L to a low of 4.0 pCi/L in a matter of hours. Let’s look at 3 main reasons why radon levels will fluctuate within a home.

1. Weather

Severe weather and barometric pressure can affect the levels of radon gas that enters the home. Heavy rain, high winds, and snow cover coupled with dropping barometric pressure affect soil gas pressure which influences the amount of radon entering a home. Heavy rain and snow cover impact soil pathways causing fluctuations in radon levels. Outdoor temperatures contribute to higher/lower radon levels because of their effect on the soil (freezing soil in winter, warming soil in summer).

2. Exhaust Equipment

Exhaust devices most homes have at least one, if not more, of the following exhaust systems

  • Fireplace
  • Central vacuum
  • Clothes dryer
  • Bath exhaust fan
  • Gas combustion appliances (furnace, heaters, range, water heater)
  • Kitchen exhaust fan

These systems push air out of the home which in turn causes radon gas to be drawn into the home. The on/off cycle of these devices will cause radon levels to fluctuate.


3. Air Pressure

Barometric pressure is the measurement of the weight of air molecules as they bear upon a given point on Earth. As you can see from the diagram when the air pressure is high it is pushing down on the earth’s surface acting against the natural rise of radon gas out of the earth’s crust. On the other hand, low pressure acts as a suction giving”lift” to radon gas by pulling it up. High pressure results in lower radon levels whereas low pressure results in higher levels.


Stack effect – is the seasonal phenomenon whereby air moves upwards within a home due to differences in temperature, density, and humidity with respect to the outside air. This “chimney” effect draws radon in from the ground and moves it upwards through the home.


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