What Is a Good Radon Level? The Honest Answer
Homeowners want a clean answer to a simple-sounding question, but radon does not offer one. Asking what is a good radon level runs into a core fact: there is no level that is officially considered safe, so the honest answer is that lower is always better. This guide summarizes EPA and Colorado Department of Public Health and Environment guidance current as of 2026 and is informational only; rely on a certified professional for testing and mitigation decisions, and consult your physician about health concerns. Below is how to think about a good level given the no-safe-level reality, the EPA’s action target, and what to aim for.
Part of our Radon Levels guide — start there for the full picture →
What Is a Good Radon Level?
The most accurate answer is that the lowest level you can reasonably achieve is the best level. The EPA does not designate a radon concentration as safe. Instead, it sets an action level of 4 picocuries per liter (pCi/L), the point at which it recommends taking steps to reduce radon, and it suggests considering action between 2 and 4 pCi/L. As a practical target, below 2 pCi/L is widely treated as a good outcome, and getting as close to outdoor levels as possible is the ideal.
So a good level is not a single number you pass or fail. It is a direction. Lower is always better, the EPA action level marks where reduction is recommended, and the realistic goal for most homes is to get well below 4 and ideally under 2 pCi/L.
Why There Is No Safe Level
Radon is a naturally occurring radioactive gas and a leading cause of lung cancer. Health agencies including the EPA and CDC describe the risk as increasing with both concentration and duration of exposure, with no threshold below which the risk drops to zero. This is the central reason the question of a “good” level cannot be answered with a fixed safe number.
Because the risk is continuous, the framing shifts from safety to reduction. Any decrease in radon concentration reduces long-term risk, so a home brought from 8 pCi/L down to 1.5 pCi/L has meaningfully improved even though neither number is declared safe. The no-safe-level principle is not meant to alarm; it is meant to explain why aiming low matters more than clearing a single bar. Our guide on safe radon levels and the honest homeowner answer explores this principle further.
The EPA Action Level as a Practical Target
Even without a safe number, homeowners need an actionable target, and the EPA provides one. The 4 pCi/L action level is the concentration at which the EPA recommends fixing the home. Below that, the agency suggests considering action between 2 and 4 pCi/L, recognizing that risk persists in that band.
Practically, this gives homeowners a tiered framework. At or above 4 pCi/L, act. Between 2 and 4, weigh action and monitor. Below 2, treat the result as good and retest periodically. The action level is a decision tool, not a safety guarantee, which is why the EPA pairs it with the message that lower is always better. Our overview of the radon testing process for Front Range homeowners puts these targets in the context of testing your own home.
What to Aim For
Setting a personal target helps turn the no-safe-level principle into a plan.
Aim Below 2 pCi/L
For most homeowners, getting below 2 pCi/L is a strong, achievable goal. It is half the EPA action level and approaches the lower end of what mitigation can deliver. A result in this range is reasonably described as good.
Recognize the Outdoor Baseline
Outdoor air averages around 0.4 pCi/L, and the national indoor average is higher. You cannot realistically reach outdoor levels indoors, but the closer you get, the better. Knowing the baseline helps you appreciate that a reading near 1 pCi/L is excellent.
Use Mitigation to Reach the Target
Homes above the action level can usually be brought well below 2 pCi/L with a properly installed mitigation system. Certified contractors design systems to reduce radon as much as practical, not merely to dip under 4 pCi/L, which aligns with the lower-is-better goal.
How Testing Supports the Goal
You cannot manage what you have not measured, and radon is invisible and odorless. Testing is the only way to know your level. The EPA recommends testing all homes below the third floor, and Colorado’s largely Zone 1 designation, the highest radon-potential category, gives Front Range homeowners particular reason to test.
Short-term tests give a quick snapshot but are influenced by weather and how the home is operated. Long-term tests, spanning more than 90 days, average out fluctuations and better represent year-round exposure. Because a good level is about long-term exposure, longer testing supports better decisions, and confirming borderline short-term results before acting is wise.
Front Range Context
Colorado’s geology and climate contribute to elevated radon potential, and much of the state, including Front Range counties, falls into EPA Radon Zone 1. The Colorado Department of Public Health and Environment encourages testing and provides resources for homeowners. For residents in Denver, Douglas, Arapahoe, Jefferson, El Paso, and neighboring counties, the no-safe-level principle has direct practical weight: testing and aiming low are sensible defaults rather than abstract advice.
How Radon Enters and Accumulates
Understanding why indoor levels climb above the outdoor baseline clarifies why a good level takes effort to achieve. Radon forms as uranium in soil and rock decays, releasing the gas into the spaces between soil particles. From there it migrates upward and seeps into homes through foundation cracks, gaps around pipes, sump pits, crawlspace floors, and other openings in contact with the ground.
Once inside, radon accumulates because the home traps it. The pressure difference between the warmer interior and the cooler soil, sometimes called the stack effect, can actively draw soil gas inside, especially in winter. A tightly sealed, energy-efficient home can hold radon more readily than a drafty one, which is why a good level is not simply a matter of how much radon is in the ground beneath the home.
This entry-and-accumulation dynamic explains why two similar homes can have very different readings and why the lowest occupied level, often a basement, tends to read highest. It also explains why mitigation works: by reversing the pressure beneath the foundation and venting soil gas before it enters, a system keeps indoor radon low. Reaching a good level usually means interrupting this entry pathway.
Comparing Your Level to Common Benchmarks
Putting a reading in context helps you judge whether it qualifies as good. The outdoor average sits around 0.4 pCi/L, the practical floor for indoor air. The national indoor average is higher, commonly cited near 1.3 pCi/L, which is why a reading in that vicinity is typical and generally fine. The EPA action level is 4 pCi/L, the point where reduction is recommended.
Against these benchmarks, a reading near 1 pCi/L is excellent, close to the indoor floor. A reading around 1.3 is typical and reasonable. Between 2 and 4, the level is below the action threshold but worth considering reducing. At 4 or above, the home exceeds the action level and reduction is recommended. Mapping your number onto this scale gives an immediate sense of whether your home is in good shape or due for attention.
The benchmarks also reinforce why lower is the goal. Even a reading of 3 pCi/L, which is below the action level, represents meaningfully more exposure than a reading of 1 pCi/L. A home does not become unsafe at exactly 4 and safe at 3.9; the scale is continuous, and getting toward the lower benchmarks reduces long-term risk regardless of where the action level sits.
How a Good Level Is Achieved and Maintained
For homes that start above the ideal, reaching a good level usually means installing a mitigation system, and understanding how it works clarifies why low results are achievable. The standard method, active sub-slab depressurization, uses a vent pipe and a continuously running fan to draw radon-laden air from beneath the foundation and discharge it outdoors above the roofline. By lowering the pressure under the slab, the system intercepts radon before it enters living spaces.
A well-designed system can often bring a home from an elevated reading down well below 2 pCi/L, which is why a good level is realistic even for homes that initially test high. Contractors seal foundation cracks, sump openings, and other entry points to improve performance, and a post-mitigation test confirms the new, lower level. The goal of a quality installation is the lowest practical reading, not merely clearing the action level.
Maintaining a good level requires modest ongoing attention. Mitigation systems include a pressure gauge that indicates whether the fan is working, and homeowners should check it periodically. Fans run continuously and eventually wear out, so occasional service keeps the system effective. Retesting every few years, and after any major home changes, confirms the good level is holding. Reaching a low reading is achievable; keeping it there is a matter of simple maintenance.
Common Misunderstandings About Good Levels
Several misconceptions cloud the idea of a good radon level. One is that reaching zero is the goal. Because outdoor air itself averages around 0.4 pCi/L, indoor air cannot realistically reach zero, and getting close to the outdoor baseline is the practical ideal rather than an impossible zero. A reading near 1 pCi/L is excellent and should not be judged against an unattainable standard.
Another misunderstanding is that a single test settles the question forever. Radon fluctuates with season, weather, and home changes, so a good reading is a snapshot that benefits from periodic confirmation. A related error is assuming that a neighbor’s good reading predicts your own. Radon depends on each home’s specific construction and the soil beneath it, so adjacent homes can differ markedly.
A final misconception is treating the 4 pCi/L action level as the dividing line between safe and dangerous. The action level is a decision point on a continuous risk gradient, not a safety switch. A reading of 3.5 is below the action level but still carries more risk than a reading of 1, which is exactly why the lower-is-better principle exists. Clearing these misunderstandings helps homeowners pursue a genuinely good level rather than chasing the wrong target.
Turning the Principle Into Action
The honest answer that lower is always better translates into a clear routine. Test the home, ideally with a long-term test or a confirmed short-term result. If the level is at or above 4 pCi/L, arrange mitigation through a certified professional and aim for the lowest practical result. If it falls between 2 and 4, decide whether to mitigate now or monitor, leaning toward reduction if children or long-term occupants are in the home. If it is below 2, treat it as a good result and retest periodically. The point is not to find a magic safe number but to keep your exposure as low as you reasonably can.
References
- EPA on radon health risk and the no-safe-level principle — U.S. Environmental Protection Agency
- Colorado radon testing resources and Zone 1 designation — Colorado Department of Public Health and Environment
- CDC information on radon and lung cancer risk — Centers for Disease Control and Prevention
Frequently asked questions
What is a good radon level?
There is no level officially considered safe, so the honest answer is that lower is always better. A reading below 2 pCi/L is widely treated as good, the EPA action level is 4 pCi/L, and getting as close to the outdoor average of about 0.4 pCi/L as possible is ideal.
Why is there no safe radon level?
Radon is a leading cause of lung cancer, and the risk rises with both concentration and exposure time, with no threshold where it drops to zero. That is why agencies frame guidance around reduction and action levels rather than a single safe number.
What level should I aim for?
Below 2 pCi/L is a strong, achievable target for most homes. Mitigation systems can usually bring elevated homes well under that, so aim for the lowest practical result rather than just dipping below the 4 pCi/L action level.
Does Colorado have higher radon risk?
Much of Colorado, including Front Range counties, falls into EPA Radon Zone 1, the highest radon-potential category. The Colorado Department of Public Health and Environment encourages testing, so Front Range homeowners have particular reason to test and aim low.
If you are a Front Range homeowner wanting to test or lower your radon level, reach out through our contact page to connect with a vetted local radon professional.
Test your home for radon
Radon is invisible and odorless, so a test is the only way to know your level. A short-term kit gives a first reading in days; a digital monitor tracks it over time.
| Product | Why | Buy |
|---|---|---|
 AirChek Charcoal Radon Test Kit | Lab fee usually included; EPA short-term protocol. | Amazon — $21.95 |
 First Alert RD1 Radon Test Kit | Widely stocked; 48-hour charcoal test. | Amazon — $16.98 |
 Airthings Corentium Home | Digital monitor with a long-term average. | Amazon — $142.99 |