What Do Radon Test Results Mean? A Complete Homeowner’s Guide to Radon Levels
- Liberty Radon Diagnostics
- 1 day ago
- 7 min read
You finally receive your radon report.
Your eyes immediately go to one number:
1.2 pCi/L
3.3 pCi/L
4.8 pCi/L
9.6 pCi/L
Now comes the question nearly every homeowner asks: “Is this good or bad?”
The answer isn’t simply “pass” or “fail.”
Understanding what your radon result means is one of the most important steps in making informed decisions about your home and your family’s long-term health. Whether you are scheduling a real estate radon testing inspection or simply checking your indoor air quality, this guide explains what each radon level means, what the Environmental Protection Agency (EPA) recommends, and what homeowners should consider next.
Why Homeowners Choose Liberty Radon Diagnostics
Independent testing only—we never sell mitigation services.
Nationally recognized testing protocols.
Accredited laboratory analysis.
Environmental and motion monitoring on every deployment.
Clear, easy-to-understand diagnostic reports.
Quick Reference: Radon Levels at a Glance
🟢 Below 2.0 pCi/L — Lower Radon Level: Retest periodically or after major renovations.
🟡 2.0 to 4.0 pCi/L — Elevated: Consider mitigation based on living habits and family risk factors.
🟠 4.0 to 8.0 pCi/L — EPA-Recommended Action Level: Mitigation is recommended.
🔴 Above 8.0 pCi/L — High: Prompt mitigation recommended.
First, What Is pCi/L?
Radon levels in the United States are reported in picocuries per liter (pCi/L).
A picocurie is a unit used to measure radioactivity—specifically, how much radioactive decay is occurring within a single liter of air. The higher the number, the greater the concentration of radon gas inside the home.
Fortunately, you don’t need a degree in nuclear physics to interpret your report. You simply need to understand what the number means and what actions, if any, should be considered.
DIY Online Testers vs. Certified Radon Testing
Before reading your numbers, it’s vital to understand where your result came from. There is a major difference between a digital monitor or kit purchased online and certified radon testing performed by a professional.
Consumer DIY Devices & Online Kits
Plug-in digital monitors or quick consumer test kits bought online are popular for casual monitoring, but they have key limitations:
Calibration Verification & Quality Control: Consumer monitors may not undergo the same routine calibration verification and quality assurance procedures required for certified professional testing programs. DIY devices are also frequently placed in improper locations (e.g., too close to drafty windows, exterior doors, high humidity areas, or HVAC vents), distorting the true average concentration.
Lack of Chain of Custody & Security: A consumer device cannot prove that strict closed-building conditions were maintained or that the device wasn’t accidentally moved, bumped, or tampered with during testing.
Non-Actionable for Real Estate: Banks, buyers, sellers, and mitigators generally cannot accept an off-the-shelf home radon test to negotiate repairs or verify system performance because it lacks official protocol adherence.
Certified Radon Diagnostics
A professional measurement conducted by an independent radon testing specialist provides a documented measurement performed according to nationally recognized testing protocols:
Strict Protocols: Placed strictly according to standards for height, distance from exterior walls, and air current isolation.
Quality Assurance & Verification: Professional measurements rely on quality-assured devices, accredited laboratory analysis, and established quality-control procedures.
Advanced Motion & Environmental Tracking: Many certified professionals use quality-control measures during testing. At Liberty Radon Diagnostics, every deployment also includes synchronized environmental monitoring and motion tracking to document testing conditions throughout the measurement period.
Unbiased & Reliable: A certified report provides buyers, sellers, and homeowners with a reliable, documented basis for making informed decisions.
There Is No “Safe” Level of Radon
One of the biggest misconceptions is that any level below 4.0 pCi/L is completely safe. That isn’t what the EPA says.
The EPA recommends:
Fix your home if the radon level is 4.0 pCi/L or higher.
Consider reducing radon levels between 2.0 and 4.0 pCi/L.
There is no known safe level of radon exposure, and reducing exposure lowers risk.
Think of the 4.0 pCi/L recommendation as an action level, not a dividing line between “safe” and “dangerous.”
Understanding Measurement Uncertainty: Like any environmental measurement, radon testing has an accepted margin of measurement uncertainty. A result of 3.9 pCi/L and 4.1 pCi/L should not be interpreted as dramatically different from a health standpoint. Instead, the EPA’s 4.0 pCi/L recommendation serves as an action guideline for deciding when mitigation is generally recommended.
Breakdown: What Different Radon Levels Mean
Less Than 2.0 pCi/L
Status: Generally considered low.
A result below 2.0 pCi/L is encouraging. No home has zero radon because it occurs naturally in the environment. The average outdoor radon level is about 0.4 pCi/L, while the average indoor level in U.S. homes is about 1.3 pCi/L.
What should homeowners do?
Keep your report for future reference.
Retest every few years.
Retest after major renovations, foundation work, or HVAC changes.
Between 2.0 and 4.0 pCi/L
Status: Elevated risk; mitigation should be considered.
This is probably the most misunderstood range. Many homeowners assume: “I’m under 4.0, so I’m fine.” In reality, the EPA recommends considering mitigation within this range because reducing radon exposure lowers long-term risk.
Example: Suppose your test measures 3.3 pCi/L.
That does not mean your home is inherently unsafe, that a home purchase should fall through, or that mitigation is automatically required. Instead, it means you’re below the formal EPA action level while still in a range where reducing radon may be worth considering based on your circumstances.
Factors to consider:
How much time your family spends on the lowest occupied level.
Whether the basement is finished or used as a living space/bedroom.
Whether children occupy the home.
Whether anyone in the household smokes (smoking and radon combined drastically increase lung cancer risk).
Between 4.0 and 8.0 pCi/L
Status: Above the EPA Action Level; mitigation recommended.
Once the result reaches 4.0 pCi/L or above, action should be taken to reduce the radon level.
Most homes can be successfully mitigated using professionally designed active suction systems. For buyers and sellers involved in radon testing in Philadelphia, this is a routine part of the real estate negotiation process.
Between 8.0 and 20.0 pCi/L
Status: Significantly elevated; prompt mitigation advised.
Although homeowners should not panic, mitigation should generally be scheduled promptly. Fortunately, even homes with high readings can routinely be brought down well below 2.0 pCi/L using proper mitigation techniques.
Above 20.0 pCi/L
Status: Very high concentration; immediate follow-up needed.
Very high readings deserve prompt, prioritized action. While these numbers can sound alarming, they are still straightforward to resolve with a properly engineered radon reduction system.
Why One Radon Test Doesn’t Tell the Entire Story
Radon levels naturally fluctuate. They can change due to:
Weather and heavy rain
Wind dynamics
Barometric pressure shifts
Seasonal heating and cooling cycles
Household ventilation and door/window use
A short-term test represents conditions during that specific testing window under standardized protocol. Reviewing our Pre-Test Protocol Checklist helps ensure your test window yields clean, reliable data without unexpected weather interference.
Understanding Radon During a Home Purchase
One of the biggest mistakes buyers make is viewing radon as a simple “pass or fail” inspection item. Experienced professionals look at it differently.
Instead, the conversation should focus on:
Was the test performed by a certified professional under proper protocol?
Were closed-house conditions strictly maintained?
Is mitigation appropriate based on the verified concentration?
Will post-mitigation testing be conducted to verify success?
If Your Home Needs Mitigation
Needing radon mitigation does not mean your home is defective.
In fact, according to the Pennsylvania Department of Environmental Protection, elevated radon levels are found in homes across all regions of the state, with approximately 40% of Pennsylvania homes estimated to have radon levels above the Environmental Protection Agency's action guideline of 4.0 pCi/L. It is a standard environmental characteristic of regional geology—not a structural flaw.
If your test comes back elevated, take a look at our guide on How to Compare Radon Mitigation Quotes to ensure you choose a qualified installer.
Don’t Skip Post-Mitigation Testing: Installing a mitigation system is only step one. The final step is independent post-mitigation verification testing.
Without testing: You’re guessing the system works.
With certified testing: You have documented proof that your indoor air is safe.
Frequently Asked Questions:
Can I rely on an online consumer device for a real estate transaction?
No. Real estate transactions generally require a certified measurement professional following strict testing protocols, documented closed-house conditions, and quality-assured equipment to ensure unbiased, valid results.
Is 3.9 pCi/L basically the same as 4.0 pCi/L?
Health risk increases on a continuum—it doesn't jump drastically between 3.9 and 4.0. The EPA uses 4.0 pCi/L as its formal action guideline, but advises considering mitigation between 2.0 and 4.0 pCi/L because lower exposure is always safer.
Does a mitigation system guarantee zero radon?
No. Outdoor air averages around 0.4 pCi/L, so eliminating radon completely is impossible. The goal of mitigation is to bring indoor concentrations down as low as reasonably achievable.
If my neighbor’s home tested low, is mine fine too?
Not necessarily. Two adjacent houses can have vastly different radon levels due to differences in foundation construction, soil permeability, sub-slab pathways, and home ventilation. Individual testing is the only way to know for sure.
Final Thoughts
A radon report is more than just a single number on a page. It’s actionable information designed to help you protect your home and family.
Rather than asking whether your home “passed” or “failed,” ask:
Was the test performed according to nationally recognized protocols using quality-assured measurement devices under valid testing conditions?
What does this specific result mean for my family’s living habits?
Should I monitor, mitigate, or simply keep the report on file?
Good decisions begin with reliable measurements and a clear understanding of what those numbers actually mean.
Need Certified Radon Testing in Philadelphia?
Whether you’re buying a home, selling a property, or simply want peace of mind about your indoor air, Liberty Radon Diagnostics provides independent radon testing throughout Philadelphia and surrounding Pennsylvania communities. Because we provide testing only—and not mitigation—you can count on recommendations that are objective and based solely on your test results.
Every deployment is performed according to nationally recognized protocols with specialized environmental tracking to give you a clear, unbiased baseline.
Explore our Radon Diagnostic Services or Contact Our Team Today to schedule an independent test for your property.
References
U.S. Environmental Protection Agency: What Is EPA's Action Level for Radon and What Does It Mean?
U.S. Environmental Protection Agency: Health Risk of Radon
U.S. Environmental Protection Agency: Consumer's Guide to Radon Reduction
Pennsylvania Department of Environmental Protection: Radon in the Home & DEP Radon Toolkit
About the Author
Moises Serrano is the owner of Liberty Radon Diagnostics LLC, an independent radon measurement company serving Philadelphia and surrounding communities. Liberty Radon Diagnostics performs radon testing and diagnostics only and does not install mitigation systems, allowing for unbiased measurement results.