What is radon? Understanding radon gas and safe levels indoors

What is radon gas?

Radon is a naturally occurring radioactive gas that comes from the breakdown of uranium in rocks and soil. You cannot see, smell, or taste radon, so a radon detector or monitor is the only way to know if it's in your home. Radon exposure is the number one cause of lung cancer among non-smokers, claiming roughly 21,000 lives every year (Source: EPA).

If you live in a house with a foundation, a basement, or a crawlspace, you are at risk from radon gas. Rest assured, though, that while high radon levels in your home can feel daunting and alarming, lowering them with either DIY fixes or professional mitigation is straightforward and usually permanent.

Here is everything you need to know about what radon is, how to understand safe vs. dangerous levels, and how to test and protect your home.

Where does radon come from?

Radon originates from the Earth’s crust. As natural uranium deposits in soil, rock, and water slowly decay, they release radon gas. Radon is detected everywhere at some level. Outdoors, the gas disperses into the atmosphere and is harmless.

The danger begins when this radioactive gas rises from the soil and reaches a building's foundation. Because the air pressure inside a home is usually lower than the pressure in the soil surrounding the foundation, and radon is a gas that will always take the "path of least resistance," your house acts like a giant vacuum that draws radon upwards. Radon can be actively pulled inside through:

• Microscopic cracks in solid concrete floors and walls
• Construction joints and gaps around service pipes
• Crawlspaces and exposed dirt floors
• Sump pumps and well water

Today’s homes tend to be better insulated and more airtight to help conserve heat and save energy. However, this also means that it’s much easier for radon gas to build up indoors. Once trapped inside an airtight, well-insulated modern home, radon can quickly rise to unsafe levels, especially if the home is not properly ventilated.

How does radon damage your health?

The risk is cumulative, meaning it depends on two factors: how high the radon level is in your home, and how long you are exposed to it. For cigarette smokers, the risk is exponentially worse. As the World Health Organization (WHO) explains, the combination of smoking and high radon exposure creates a much higher risk of developing lung cancer.

What are safe radon levels, and how is radon measured?

Radon is a carcinogen, and there is no completely safe level of radon exposure, so health experts recommend keeping levels as low as is practically possible.

In the United States, radon is measured in picocuries per liter of air (pCi/L). A picocurie is a unit of radioactivity that measures how many radioactive decay events occur per second in one liter of air. Note that outside the US, radon is measured in becquerels per cubic meter (Bq/m³).

However, the US Environmental Protection Agency (EPA) has established clear guidelines to help homeowners understand their risk and know when to take action.

• Under 2.0 pCi/L (74 Bq/m³): Low risk. While no level is entirely risk-free, the EPA considers levels in this range relatively normal and low-risk.
• 2.0 to 4.0 pCi/L (75 to 150 Bq/m³): Moderate risk. The EPA strongly recommends that you consider fixing your home if your levels fall in this range, particularly if you spend a lot of time in the lowest level of your house (like a basement bedroom or office).
• 4.0 pCi/L and above (150 Bq/m³ or higher): High risk / Action level. This is the official EPA Action Level. If your home tests at 4.0 pCi/L or higher, you must take immediate steps to install a radon mitigation system.

To put these numbers into perspective, living in a home with a radon level of 4.0 pCi/L exposes you to the same amount of radiation as getting 200 chest X-rays every year, or smoking 8 cigarettes a day (Source: Clinical and Translational Oncology: An overview on the relationship between residential radon and lung cancer: what we know and future research, Ruano Ravina et al, 2023).

Health Canada recommends that action be taken to lower radon levels in a dwelling whenever the average annual radon concentration exceeds 200 Bq/m³ in the normal occupancy area. The World Health Organization (WHO) also recommends a reference level of 100 Bq/m³, if possible.

It’s also important to note that radon can vary enormously from house to house, and street to street. The only way to know your home’s level is to test.

To gain some idea of the varying levels in your region, Airthings’ radon map pulls data from connected radon devices to give a rough idea of your neighborhood’s radon level. Try checking radon levels in your area with the Airthings radon map.

How to test and monitor radon in your home

Radon levels fluctuate from day to day, season to season, and even according to how you use your home. The same home might test low in the summer when the windows are open, but spike dangerously high in the winter when the house is sealed tight and the heating system alters the indoor air pressure.

Because of these fluctuations, a one-time, short-term radon test kit often fails to show the true danger. The EPA recommends long-term testing to fully understand your home’s average radon exposure. This long-term monitoring helps give a broader, more accurate picture and will help you decide if you do indeed need to take action to lower your home’s radon levels.

Using a continuous, digital radon monitor, such as the Airthings Corentium Home 2 or View Plus, is a simple way to understand your radon levels and protect your family.

Read our guide, How to test for radon, for more details on how to test your home.

• For continuous radon monitoring: The Airthings Corentium Home 2 provides accurate, long-term daily, weekly, and continuous averages so you can see exactly how your home breathes over time. To see your radon data in more detail and to look back at levels over time, the Corentium Home 2 connects to the Airthings app. The “Radon Insights” feature guides you through the monitoring process, helps you understand what your radon levels mean, and tells you whether you need to take any action. The Corentium Home 2 has bonus sensors for temperature and humidity, making it ideal for keeping on top of your overall air quality.
• For the complete air quality picture: The Airthings View Plus monitors radon alongside particulate matter (PM), volatile organic compounds (VOCs), CO₂, temperature and humidity, making it ideal for keeping track of radon and general air quality in your main living spaces. Deeper insights into all these air quality factors are available in the Airthings app, alongside Radon Insights.

CNET’s Smart Home editor Tyler Lacoma tested the Corentium Home 2 and recommended it as one of the best ways to assess radon levels at home, praising its simplicity and the addition of temperature and humidity sensors. Read the article on CNET: “I set my radon worries to rest with a gadget that puts testing kits to shame”

What to do if your radon levels are high?

If your radon detector shows a long-term average at or above 4.0 pCi/L (or 150 Bq/m³), do not panic. Radon is a problem that is straightforward to fix.

The first step is to try some simple DIY fixes, such as sealing cracks in foundations or around plumbing and increasing ventilation. Try these and keep monitoring to see if they’ve been effective. If levels remain high, it’s important to contact a radon mitigation professional for advice. They will assess what other measures to take, and will typically install a sub-slab depressurization system. This is a specialized vent pipe and fan system that pulls the radon gas out from underneath your foundation and vents it safely above your roofline before it ever enters your living space. You can review likely costs associated with radon mitigation in our Airthings guide, What does radon mitigation cost?

Acting on high radon levels: Airthings case study

For Judith Spence, radon wasn’t something at the top of her mind when she moved from the city to the Canadian countryside for a healthier life. After discovering uranium mining in the region and testing her home with an Airthings monitor, Judith discovered that her home’s radon levels were around 100 times higher than the average level found outdoors. Judith’s husband worked to install a radon mitigation system and seal cracks around the foundations. Once this was up and running, their Airthings monitor showed radon levels dropping almost immediately after installation, helping them regain peace of mind that their home was safe and healthy.

What happens after I mitigate for radon?

After any step to lower radon levels, whether through DIY fixes or a professional radon mitigation system, it’s crucial to keep monitoring year-round. This will help you understand whether the measures succeeded and, critically, that they continue to work. A continuous digital radon detector is a great way to keep on top of radon levels and have peace of mind that your family is breathing safe air.

Sources

• US EPA (Radon health risk)
• US EPA (EPA action level for radon)
• American Lung Association (ALA)
• Health Canada
• WHO (World Health Organization)