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Why are radon concentrations higher in the winter?

In short: the stack effect. The stack effect, sometimes called the “chimney effect”, is a term to describe the airflow patterns in buildings. When outdoor temperatures drop, warm indoor air rises inside a building. This in turn pulls colder air from the lower floors. Soil gas is then pulled into the building to replace this air.

In our industry, the joke is: “your house sucks”. What we mean by that is: your house sucks soil air and pulls it inside for you to breathe. Soil air contains radon, a Class A carcinogen.

Ever wonder why radon action month is in January? Simple: the coldest month of the year is typically when radon levels are highest, since the stack effect is strongest. If you’re safe in January, you’re typically safe in August, but rarely vice versa. So January is when you should test for radon.

Radon-222 decays every 3.8 days, so leaving your windows closed all winter is not the reason for the spike. Radon in your home has to constantly be reintroduced. Closed-house conditions can increase levels temporarily, but they will level out. This is why ventilation is not a good long-term solution to a radon problem. First, when radon levels are high enough, even ventilation cannot lower them to a safe level. Second, ventilation without an air exchanger is extremely energy inefficient. That air you just paid to heat or cool, now it’s out the window. Soil depressurization is the simplest, most effective and most energy efficient way to reduce radon levels.

The absolute best way to maintain your radon system is to perform a lab-certified short term or long term radon test every two years during the winter months, when radon levels are highest. This has been the EPA recommendation for over two decades. Just because you have an existing system, does not guarantee it works. The first step is to test and ensure your levels are acceptable.

Read our next article on radon system maintenance for the next steps, but the first step is always test, test, test, especially if we are at a time of year when radon levels are highest!

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