Whats Radon Test: A Plain-Language Guide
Most people who search “whats radon test” have heard the phrase somewhere — a home inspector mentioned it during a walkthrough, a neighbor brought it up at a barbecue, a real-estate agent listed it as a recommended add-on — without ever getting a plain explanation of what the test actually is. This guide is written for that exact reader. It assumes nothing prior, covers the basics in plain language, and answers the questions a curious homeowner would ask before deciding whether to test. The summary reflects EPA, CDPHE, and CDC guidance current as of 2026.
Whats Radon Test, Explained Plainly
A radon test measures the amount of radon gas in the air inside a home. Radon is a radioactive gas that you cannot see, smell, or taste. It comes up out of the ground naturally — from uranium and radium in rock and soil — and seeps into homes through cracks in foundations, sump pits, and gaps around plumbing. Once inside, radon can build up to levels that pose a long-term lung-cancer risk if breathed daily over many years.
The test is a small device placed in the lowest occupied floor of the home for a few days. After the exposure period, the device is either mailed to a lab (for passive kits) or read on the spot (for continuous monitors). The result is a number in picocuries per liter (pCi/L). EPA recommends taking action if the number is 4 pCi/L or higher.
Why Anyone Tests for Radon at All
The reason is straightforward: radon is the second-leading cause of lung cancer in the United States after smoking, and the only way to know whether a home has elevated radon is to test. Indoor radon levels vary widely between homes, even between adjacent houses on the same block. Two neighbors can sit side by side and have radon levels that differ by a factor of ten.
CDC’s radon program estimates radon causes about 21,000 lung cancer deaths each year in the U.S. Most of those cases involve people who smoked or were exposed to secondhand smoke; radon and tobacco multiply each other’s risks. Non-smokers can also develop radon-induced lung cancer from sustained exposure to elevated indoor concentrations.
Colorado specifically sits in the highest-risk EPA radon zone. About half of homes along the Front Range — Denver, Boulder, Douglas, Jefferson, El Paso, and surrounding counties — test above the EPA action level. The pillar overview at radon testing in Colorado for Front Range homeowners covers the geographic context.
How the Test Works
A radon test is one of two basic types: passive or active.
Passive Test
A small canister or detector sits in the home for a few days, collecting a sample of indoor air. After the exposure period, the homeowner seals the device and mails it to a lab. The lab analyzes it and emails a result back within about a week.
The most common passive test is the activated charcoal canister kit. It costs $15 to $25 including lab analysis and is sold at hardware stores or online. An alternative is the alpha-track detector, which runs for 90 days to one year and gives a better picture of annual average radon levels.
Active Test
A continuous radon monitor is an electronic device that reads the radon level hour by hour and displays the running average on a screen. Consumer models cost $100 to $300. Professional monitors used by inspectors cost more but produce the same kind of result.
Active monitors are great for verifying that the home was kept closed during the test (the temporal data shows whether someone opened a window). They are also useful for post-mitigation verification.
The companion guide what is radon test methodology covers the test in more technical detail.
What “EPA Action Level” Actually Means
EPA’s action level for radon is 4 pCi/L. Test results at or above this level prompt the EPA recommendation to install a radon mitigation system. Below 4 pCi/L, mitigation is optional. Below 2 pCi/L is generally considered low.
The action level is not a hard threshold for safety. The World Health Organization recommends a lower action level of 2.7 pCi/L. There is no level of radon exposure that is considered completely safe — the risk follows a dose-response curve that rises smoothly with exposure. The 4 pCi/L figure is a practical action threshold based on cost-effectiveness of mitigation and the lung-cancer risk numbers EPA uses.
What Happens If the Result Is High
An elevated radon test result is not an emergency. Lung-cancer risk from radon accumulates over years and decades of exposure. A high reading means the homeowner should install a mitigation system within a reasonable timeframe — not that the family needs to evacuate the house immediately.
Radon mitigation usually involves sub-slab depressurization: a fan-driven vent system that pulls radon out from under the foundation slab and exhausts it above the roof. A certified contractor designs and installs the system. Cost: typically $1,200 to $2,500 for a Front Range home. The system runs continuously and reduces indoor radon levels by 80 to 99 percent in most cases.
American Lung Association radon resources publish plain-language explanations of mitigation options.
When to Test
EPA and CDPHE recommend that every home be tested for radon. The right time to test depends on the situation.
- Buying a home: Test during the inspection contingency window. The result becomes part of the negotiation.
- Currently in a home that has never been tested: Test now. The cost is low and the information is valuable regardless of result.
- Previously tested at a low level several years ago: Re-test every 2 to 5 years. Levels can change with foundation movement, HVAC changes, or new construction in the area.
- After major renovations: Test again, especially if foundation work, HVAC system replacement, or basement finishing was involved.
- After mitigation system installation: Test to verify the system is working, then annually.
What the Test Cannot Tell You
A radon test reports the indoor air concentration during the test period. It does not identify how radon is entering the home — that requires a separate diagnostic during mitigation system design. It does not predict whether radon will increase or decrease in the future. It does not estimate health risk for a specific individual; that depends on age, smoking status, and cumulative lifetime exposure.
A short-term test is also a snapshot. Radon levels vary by hour, day, and season. Winter heating-season levels are typically higher than summer levels because tighter house conditions concentrate the gas. A summer short-term test that lands just below 4 pCi/L may correspond to a winter level above 4 pCi/L in the same home.
Doing It Yourself vs Hiring an Inspector
For routine homeowner curiosity, a DIY kit is perfectly adequate. The lab analysis is identical whether the homeowner deployed the kit or an inspector did. The companion guide can you test for radon yourself with EPA protocols walks through the DIY procedure.
For real-estate transactions, hiring a certified tester or having the home inspector run the test produces stronger documentation. Chain-of-custody and EPA-protocol verification matter more when the result becomes part of a contract negotiation.
Common Misconceptions
“My home is new, so it does not have radon.”
Building age does not predict radon. New homes can have elevated levels if foundation venting is inadequate. EPA-published data shows no consistent age-versus-radon relationship.
“My neighbor tested low, so my home is fine.”
Adjacent homes can have very different radon levels because of differences in foundation type, slab cracks, soil composition, and HVAC operation. Each home needs its own test.
“Radon only matters in basements.”
Radon enters through the foundation and can accumulate throughout the home, especially in tightly sealed energy-efficient construction. Slab-on-grade homes without basements can also have elevated radon. CDPHE documents radon findings in homes of every foundation type.
“Radon goes away if I just open windows.”
Ventilation does reduce levels temporarily but does not solve the entry pathway. Once windows close, radon rebuilds. Mitigation systems address the source.
Cost Summary
- Activated charcoal DIY kit: $15 to $25.
- Alpha-track long-term DIY kit: $20 to $40.
- Consumer continuous radon monitor: $100 to $300.
- Professional short-term test: $150 to $250.
- Mitigation system installation: $1,200 to $2,500 for typical Front Range home.
- Post-mitigation re-test: $150 to $250.
Where to Buy a Radon Test
Hardware-store chains carry activated charcoal kits and a small selection of alpha-track detectors. State and county health departments sometimes offer free or subsidized kits for residents — CDPHE periodically runs programs where Colorado residents can request a free test kit. Online retailers carry a wide range of kits and consumer continuous monitors at competitive prices.
The packaging should name the analyzing laboratory and reference NRPP or NRSB listing. Kits from no-name brands or with unclear lab affiliations are best avoided in favor of established kit manufacturers whose chain-of-custody documentation has been independently verified.
How the Test Results Look on a Lab Report
A typical lab report contains the homeowner’s contact information, the kit ID number, the deployment dates and duration, the analyzing laboratory’s certification information, the measured radon concentration in pCi/L, and a brief explanation of the EPA action level. Some reports include a comparison chart showing the result against the action threshold.
Reports do not typically include mitigation contractor referrals (that is a separate step) or detailed health-risk calculations (that requires personal risk factors the lab does not have). The report is intentionally focused: this is the radon level you measured, here is what it means.
What If My Spouse or Family Disagrees About Testing
Radon testing sometimes encounters household disagreement. One partner may consider the test important; the other may consider it unnecessary. A few framing points help.
- The test cost is small ($20). The information is valuable regardless of result.
- The EPA recommendation is universal — every home, regardless of perceived risk.
- Front Range Zone 1 designation means roughly half of homes test above the action level.
- A negative result is reassuring. A positive result identifies an addressable hazard. There is no scenario where the test was a bad investment.
For families with young children, the case for testing is particularly strong because cumulative lifetime exposure begins at birth.
Long-Term Health Considerations
Radon-induced lung cancer typically develops decades after sustained exposure. A short-term high reading does not represent an immediate medical emergency — the homeowner does not need to evacuate the home. The proper response is to install a mitigation system on a reasonable timeline (weeks to months, not minutes to hours).
For homeowners already concerned about lung-cancer risk for other reasons (heavy smoking history, family history, occupational exposure to other lung carcinogens), the radon contribution to cumulative risk is particularly important. American Lung Association publishes the multiplicative interaction between radon and smoking — a smoker exposed to elevated radon has substantially higher combined risk than either exposure alone would predict.
Radon in Drinking Water
Radon dissolves in groundwater. Private wells drawing from radon-bearing rock can deliver elevated radon to the home’s drinking water system. Radon escapes from water at fixtures — particularly showers and washing machines — and contributes to indoor air levels.
Most Front Range homes are on municipal water (treated and aerated before distribution, reducing radon to negligible levels). Homes on private wells should consider radon-in-water testing separately. EPA recommended action level for radon in water is 4,000 pCi/L (different units than the air test). Water treatment options include granular activated carbon filters and aeration systems.
References
- EPA radon program and Citizen’s Guide to Radon — U.S. Environmental Protection Agency
- CDC radon and health — Centers for Disease Control and Prevention
- CDPHE radon and indoor air program — Colorado Department of Public Health and Environment
- American Lung Association radon and health — American Lung Association
Front Range homeowners new to radon testing who want guidance from a vetted local inspector can reach a qualified professional through our contact page.