Radon levels are constantly changing – hourly, daily, and seasonal fluctuations are all common. If you have tested multiple times and received back differing results, don’t be too alarmed – this is common! There are many different factors contributing to radon levels, but essentially, changes in the air pressure inside and outside your home affect the radon levels of your home.

Radon gas is a naturally-occurring radioactive gas found in the soil. As it is a gas, it is continually seeking a lower air pressure area; basically, moving from the soil to the air. Just like water always tries to find the easiest path downhill, radon tries to find the easiest path out of the soil and into the air. When water is running down a steep hill, it flows faster than on a gentle slope. Likewise, radon flows faster when there is a bigger difference in pressure between the high pressure soil and the low pressure air. This principle of pressure differences is the main driving force that causes radon to enter your home, and also causes radon levels to change.

Weather is one of the most common factors affecting radon levels. Changes in weather – particularly extreme weather events – can change the pressure differences and therefore change how radon enters your home. Some weather events, like storms, typically cause radon levels in a home to rise. Other events, like heavy winds, can cause radon levels to either rise or fall. Essentially, weather events can cause your radon levels levels to either rise or fall. All kinds of weather affect your test – and there’s no easy way to know exactly which way your test was affected. Typically, light weather events – like a light rainfall, low winds, mild snowfall, etc., do not dramatically affect radon levels. But, heavy weather events – severe storms, high winds, etc., often do affect radon levels tremendously.

Here’s a list of some types of weather that affect reading:

  • Rain/storms – Storms systems bring in lower pressure air around your home. This lower pressure causes radon to “flow” from the soil to the air even faster than normal. If there is heavy rainfall and the ground becomes saturated with water, this makes it harder for radon to find a path through the soil outside the home. This increase in pressure below the surface can increase the radon entering your home – your home has now become the easiest path for radon to reach the air! Radon’s normal “escape routes” can become blocked creating heavier pressure on the soil and pushing the radon gas into lower pressure areas like your home, school, or business. Conversely, rainfall could open up some new “routes” for the radon to move easier through, decreasing your levels.
  • High winds – Wind also has an effect on the air pressure. High winds can either be pushing out the radon (creating high pressure in the home) or “vacuuming” it in (creating low pressure in the home). In most cases, high winds increase radon levels in homes.
  • Cold winter weather – snow, ice, colder temperatures, etc. Each of these types of weather causes the ground to be more compact and creating pressure for radon to escape elsewhere. In addition to that, colder weather usually means that your home’s heat gets turned up! Heaters can also pull more radon through the building and cause levels to rise. Hot air rises, and if that air is rising and escaping your home, new air must enter your home to fill up that empty space. Some of that air will come from the soil and this can introduce radon into the home. Winter usually yields the highest levels of radon!

If you’ve already started your radon test and a severe weather event occurs, you should continue running the test. Running the test for the longest period of time possible is recommended when severe weather occurs – so aim for 96 hours. Running the test for a longer period of time helps to compensate for any sudden changes in radon levels caused by weather. However, the results from the test may still not be a good indication of your normal radon levels, so it’s wise to run another test once the weather is back to normal.

Sometimes a home’s air exhaust devices can have an effect on radon levels. If any of these circulate from outside or vent air to the outside, that can either be drawing in radon or venting it out. For example, a bathroom fan that vents air out of the roof can increase radon levels – the air that leaves the house has to be replaced. The new air that comes into your home can contain radon. A HRV, ERV, or heat exchanger can sometimes lower radon levels – it’s introducing new air from outside where radon levels are low. Here are a few appliances that can affect radon levels:

  • Furnaces
  • Open wood fireplaces
  • Clothes dryers
  • Central vacuum cleaners
  • Bathroom fans
  • Space heaters
  • Water heaters
  • Oven vents

Factors other than weather can also affect radon levels in a home. Foundation shifts, construction on the home, or changes in the heating/cooling systems can all affect radon levels. Sometimes, changes in the ground far beneath your home can make it easier or harder for radon to enter your home.

Since there are many reasons that radon levels can change, the EPA recommends that you test for radon periodically, regardless of the results of your initial test. If your test results are low (less than 2 pCi/L), you should test every 2-3 years. For tests higher than 2 pCi/L, testing yearly or more frequently is a good idea.

If you’ve performed 2 or more radon tests and the results are different, you should average the readings to decide what to do next. You can also consider testing using a Long Term device. Long terms test for 90 days up to 1 year. This will provide an average radon level over long periods of time and smooth out any fluctuations in radon levels.

You may be asking yourself “What’s the point in testing if radon levels change so much?” While radon levels do change, studies have shown that a short term test is a good way to check your radon levels, as long as you follow closed house conditions. When closed house conditions are observed, short term radon tests provide an accurate representation of your home’s typical radon levels in about 90% of tests. So, while short term tests aren’t always the best solution to every situation, they are usually a very good first step as they are much faster, easier to use, and less expensive than other testing methods.