Radon: Does It Matter When I Test?

It’s summer, you just purchased your dream home, and the inspection passed with flying colors. No major structural issues, no electrical or plumbing headaches to deal with, and your radon test came back low. Does this mean you never have to worry about radon mitigation?

The answer to that question may surprise you.

Seasonal changes can cause radon levels to fluctuate. This means that the test conducted during the summer will likely be different than if it were completed during the winter.

When Are Radon Levels Highest?

So, is radon worse in the summer or winter? Well, here in middle Tennessee you are likely to have higher radon levels in the winter. As radon gas rises through the soil it looks for the path of least resistance to escape into the atmosphere. In the winter, the ground is frozen making it much more difficult for the gas to easily escape. Similarly, ice and snow make it impossible for the gas to escape. Then there’s the warm footprint of your house and the subsequent “stack effect.” The warm air inside your home is constantly rising and finding ways to escape through the upper levels of the house.

This illustration shows how stack effect creates a negative pressure in the lower levels of your home, drawing in more soil gasses, including radon, through your slab or crawlspace.

Does Rain Affect Radon?

Does weather affect radon? Does rain affect radon? Yes! While a light rain isn’t likely to have a strong effect, heavy rains and thunderstorms certainly can. Similarly to how sleet and snow can create a blockade preventing gases from escaping the ground around your house, water saturated ground can also prevent the gases from easily escaping into the atmosphere. In fact, AARST standards say to “Avoid testing during unusual local severe weather if the test period is less than 4 days.” The protocol goes on to state that if severe conditions do arise during testing, a retest may be necessary. Any test completed by a certified professional, like home inspector or radon pro, should have an hour-by-hour chart on the report that you can review to see if there was a significant spike during the time of rain.

Do I Need To Retest For Radon?

So what should you think about the radon test that passed during the summer? Well, you should plan on retesting once cold weather comes around. It’s very possible your radon levels will still be within the safe range (<4.0pCi/L), but you won’t know that for sure without conducting another test. Luckily, testing these days is easy. You can hire a professional, get a free testing kit from the state, or (and this is the option we typically recommend to homeowners) you can purchase your own long-term testing device from Amazon. There’s many options to choose from, but we love the Airthings brand, which is commonly used by home inspectors. We’ve even made it easy on you by compiling our favorite Airthings devices here!