Radon Test What Is It: A Plain-Language Guide
Radon test what is it, asked the way someone might ask after hearing the phrase for the first time? A radon test is a measurement of a naturally occurring radioactive gas inside your home’s air. The gas comes from the soil under the house, seeps up through the foundation, and accumulates indoors. Because radon has no smell, no color, and no taste, the only way to know if it is present at harmful levels is to measure it with a kit or a professional inspection device. This guide answers the question the way it usually gets asked — by a homeowner who has just heard “you should test for radon” and wants to understand what that means in plain terms. Content reflects EPA, CDPHE, and lung-health guidance current as of 2026 — engage a certified professional for mitigation decisions.
Radon Test What Is It: The Basic Answer
A radon test measures the amount of radon gas in the air inside your home over a set period of time. The result comes back as a number in units called picocuries per liter, or pCi/L. The Environmental Protection Agency considers anything above 4 pCi/L high enough to warrant fixing. Anything between 2 and 4 pCi/L is worth thinking about. Below 2 pCi/L is generally fine, but you should test again every few years because levels can change.
That is the whole concept in a paragraph. The rest is just detail about how the measurement gets done, why the gas matters, and what to do with the result.
What Radon Actually Is
Radon is a chemical element. It is a noble gas, meaning it does not react with other substances and stays a gas at normal temperatures. It is also radioactive, meaning its atoms break down over time and release tiny bursts of energy as they decay into other elements. Radon forms naturally from uranium in soil and rock. Almost every soil contains some uranium, so almost every home has some radon. The question is how much.
The gas is invisible. You cannot see it, smell it, or taste it. Radon does not make a noise or leave residue. It enters homes through cracks in foundations, gaps around pipes, openings around sump pits, and even through the porous concrete of a slab. The gas then collects indoors because buildings are designed to keep air in, not let it freely exchange with outside air.
Why Radon Matters for Health
The EPA estimates that radon causes about 21,000 lung cancer deaths per year in the United States. That makes it the second-leading cause of lung cancer after smoking. The American Lung Association and CDC publish similar figures. The mechanism is straightforward: when radon decays in your lungs, the decay produces alpha particles that damage cells, and that damage can lead to cancer over years and decades.
The risk depends on how much radon you breathe and for how long. Living for thirty years in a home with very high radon raises lung cancer risk much more than living for five years in a moderately elevated home. The risk is also higher for smokers, because radon and tobacco smoke interact in a way that makes each more dangerous than either alone. For a never-smoker, radon is the leading cause of lung cancer.
How the Test Works in Plain English
A radon test does one thing: count how much radioactive activity is happening in your air. Different devices do the counting in different ways, but the result is the same kind of number.
A charcoal canister test works by sitting open in your home for two to seven days. Charcoal grabs the radon gas as air moves past it. After the test period, you seal the canister and mail it to a lab. The lab measures how much radioactive activity the captured radon produces and calculates the original concentration in your air.
An alpha-track detector works by exposing a thin piece of plastic to your air for three months to a year. Radioactive decay particles strike the plastic and leave microscopic damage tracks. The lab etches the plastic with a chemical bath to make the tracks visible, counts them under a microscope, and calculates the average concentration over the whole exposure period.
A continuous radon monitor works like an electronic counter. It sits in your home for at least 48 hours, recording the radon level every hour. When the inspector retrieves the device, the data downloads to a computer and the report shows the average concentration plus any spikes during the test period.
Why Colorado Homeowners Hear About This So Often
Colorado has more naturally occurring radon than most of the country. The Front Range — Denver, Douglas, Arapahoe, Jefferson, Boulder, Adams, El Paso, Broomfield, Elbert counties — sits on geology that produces a lot of radon. The EPA classifies all of Colorado as Zone 1, which is the highest-risk zone in the national map. CDPHE data shows roughly half of homes tested in Colorado have radon above the action level.
If you live in Colorado, you have a coin-flip chance that your home will test high. That probability is the reason real-estate agents, home inspectors, and CDPHE all push so hard on testing. It is also the reason buyers in the Denver metro almost always add a radon test to their home inspection package. See the radon testing in Colorado pillar for the regional risk picture.
How Much It Costs
The cheapest option is a do-it-yourself charcoal canister kit, which runs $15 to $30 including the lab fee for analysis. You buy the kit at a hardware store or online, leave it in your basement for a few days, and mail it back. Results come back in a week or two.
A long-term alpha-track detector costs $25 to $50 and runs for several months to a year. The longer test produces a more reliable average reading but takes longer to get an answer.
A professional radon inspection with a continuous monitor runs $150 to $200 in the Denver metro. The inspector handles everything from device placement to data download and produces a formal report. This is the option most buyers use during a real-estate transaction.
A consumer-grade digital radon monitor for ongoing measurement at home runs $130 to $300. These devices, like Airthings or Radonova, give you real-time readings on a smartphone app and let you watch the level over time. They are popular with homeowners who already mitigated and want to confirm the system keeps working. See the what are radon detectors guide for a device-by-device comparison.
What the Number Means
You will get back a number in pCi/L. Here is what each range means in plain language.
Below 2 pCi/L: low. No action needed. Test again in two years.
Between 2 and 4 pCi/L: moderate. You might consider mitigation, especially if you spend a lot of time in the basement or lower level. EPA leaves this range up to the homeowner.
Above 4 pCi/L: high. EPA recommends mitigation. The typical fix is a vent system installed beneath the slab that pulls soil gas out before it can enter the home.
Above 10 pCi/L: very high. Mitigation should not wait.
What Happens If the Test Comes Back High
A high result is not a crisis. It is information. The next step is to hire a certified radon mitigation contractor to assess the home and design a system. Most Front Range homes can be fixed for $1,200 to $2,000. The contractor installs a vent pipe from beneath the foundation slab to above the roof, adds a fan to pull soil gas continuously, and seals visible entry points like sump pits and slab penetrations.
After installation, a follow-up test confirms the system is working. A properly designed system typically brings radon levels below 2 pCi/L. The fan runs continuously and costs about $5 to $10 per month in electricity. The system requires periodic checks but lasts decades.
The Difference Between Testing and Fixing
This is the most common confusion among first-time radon learners. Testing measures the level. Fixing reduces the level. Testing is a kit or a device. Fixing is a contractor installing hardware. The two activities are different and happen in sequence: you test first, then if needed you fix, then you test again to confirm the fix worked.
Putting tape over foundation cracks does not fix radon. Buying a kit does not fix radon. Only an engineered mitigation system reduces radon to safer levels. The kit is the measuring tool. The mitigation system is the treatment. See what is a radon test kit used for for the measurement-versus-mitigation distinction.
How Often to Test
EPA recommends testing every two years even after a low initial reading. Radon levels can change over time because of weather patterns, soil moisture, and structural changes to the home. A house that tested at 1.5 pCi/L five years ago could test higher today.
If your home has a mitigation system installed, test every two years to confirm it still works. Test again after any major renovation that affects the foundation or HVAC system. If your test comes back near the 4 pCi/L threshold, retest with a long-term detector to see whether the result holds up over a longer averaging period.
Common Questions People Ask First
A few questions surface repeatedly when someone hears about radon for the first time. Can you smell it? No, it has no odor at any concentration. Can a regular smoke detector catch it? No, smoke detectors use either ionization or photoelectric sensors designed for combustion particles, not radioactive gas. Does opening windows fix it? Opening windows reduces the concentration temporarily but does not solve the problem because soil gas keeps entering. Closed-up tight homes can have higher readings than drafty older homes, which is why testing under closed-house conditions captures the worst-case condition occupants typically experience.
Is radon a new problem? No, radon has always been present in homes — the awareness of it as a health risk is more recent, dating to the 1980s when EPA established the residential testing program. Did builders historically design for radon? Most pre-1990 homes were built without radon-resistant features. Some Front Range counties now require radon-resistant features in new construction, but the existing housing stock predates those rules and benefits most from testing.
What to Tell Family Members Who Are Skeptical
Some family members react to radon information with skepticism — “we have lived here for years and we are fine,” or “nobody I know has had radon problems.” The skepticism is understandable because radon does not produce visible symptoms or obvious damage. The right response is not to argue but to offer the test as a low-cost way to settle the question. A $20 kit takes a few days and produces a number. If the number is low, the skeptic is right and the household has spent $20 to confirm it. If the number is elevated, the household has spent $20 to gain information that justifies a one-time mitigation expense. Either outcome is better than the status quo of not knowing. The whats radon test guide covers the same question from a different angle.
References
- EPA citizen’s guide to radon — U.S. Environmental Protection Agency
- CDPHE radon program — Colorado Department of Public Health and Environment
- American Lung Association radon resources — American Lung Association
- CDC radon information — Centers for Disease Control and Prevention
Front Range homeowners new to radon testing can reach out through our contact page for a connection to a certified radon professional.