EPA-Protocol Test Result Reading Guide
Radon Test Results — Read, Troubleshoot, Decide
Confused by your radon test result? This guide walks through every common reading scenario, troubleshoots the most frequent test-kit errors, and shows exactly how to map your number to the EPA action level. All guidance follows EPA Citizen's Guide to Radon (EPA 402/K-12/002) and AARST-NRPP measurement standards.
Start here — match your result to EPA guidance
Type Your Radon Reading and Get an EPA-Aligned Answer
Enter the pCi/L value from your test report below. The calculator returns the EPA risk tier and recommendation for that specific reading.
pCi/L
Enter the picocuries-per-liter value from your charcoal canister or continuous radon monitor (CRM) report.
How the calculator maps test results to EPA guidance
| Radon level (pCi/L) | Risk tier | EPA-aligned recommendation |
|---|---|---|
| 0.0 – 1.9 | Below average — low | No action needed. Re-test every 2 years or after major renovation. |
| 2.0 – 3.9 | Elevated — EPA "consider mitigating" | Consider mitigation, especially with smokers, children, or lower-level bedrooms. Run a long-term (90+ day) test for confirmation. |
| 4.0 or higher | EPA Action Level — fix the home | Install an active radon mitigation system. EPA recommends fixing the home as soon as practical. |
Common test-kit problems + corrective action
Source: EPA Indoor Radon Quality Assurance Plan (EPA 402-R-92-004), AARST-NRPP MS-PC 2014 measurement protocol standards, and field troubleshooting data from certified mitigation partner network.
Radon Test Kit Troubleshooting Reference Table
Common reasons a radon test result is inaccurate, unreliable, or unusable — with the EPA-aligned corrective action for each scenario.
| Test result symptom | Probable cause | Corrective action |
|---|---|---|
| Charcoal canister exposed >96 hours | Charcoal saturation; lab cannot reverse-engineer concentration | Discard. Purchase a fresh charcoal kit and re-test under closed-house conditions for 48-96 hours. |
| Charcoal canister exposed <48 hours | Insufficient adsorption for lab calculation | Discard. Re-test for full 48-96 hour window minimum. |
| CRM showed huge spike during a rainstorm | Falling barometric pressure pulled soil gas upward | Use 48-96 hour AVERAGE, not peak. If average ≥4.0 pCi/L, mitigation is recommended. |
| First test 8.0 pCi/L, second test 2.0 pCi/L | Likely weather-driven variability or open-window during one test | Re-test under controlled closed-house conditions. Use the higher reading as the action signal if testing was done correctly both times. |
| Result exactly 4.0 pCi/L | Borderline at EPA action level | Mitigation recommended. EPA action level is "at or above" 4.0 — exactly-4.0 is in the action tier. |
| Result in 2.0-3.9 pCi/L range | EPA "consider mitigation" zone | Mitigate if smokers, children, or basement bedrooms present. Otherwise, re-test in 2 years. |
| Result below 1.0 pCi/L on long-term test | Below US national average | No action. Re-test every 2 years or after major renovation. |
| Digital home monitor reads ±20% from professional CRM | Consumer-grade calibration tolerance | For closing or mitigation decisions, re-test with AARST-NRPP-certified CRM or short-term lab canister. |
| Alpha-track result took 90+ days | Long-term test method (normal) | Result more accurate than short-term for chronic-exposure assessment. Use for re-test verification, not for transaction timelines. |
| Basement 8.0 pCi/L, first floor 2.0 pCi/L | Stack-effect concentration in lowest level | Use basement reading if basement is finished/occupied. If unfinished/unused, weight by time spent in each space. |
| Result from open-window test | Outdoor air diluted indoor concentration | Invalid for EPA protocol. Re-test with windows + doors closed 12+ hours before and during testing. |
| Conflicting short-term vs long-term results | Time-period variability normal; long-term is more reliable | Long-term test reflects actual chronic exposure. Use that result for mitigation decision unless short-term was significantly higher. |
| Brand-new home test came back 12.0 pCi/L | uranium-bearing Devonian Ohio Shale / fractured-bedrock geology likely | Mitigate immediately. New construction does NOT preclude high radon — geology drives the reading. |
| Post-mitigation test still reads 3.5 pCi/L | System working but borderline | System is reducing radon (likely from much higher pre-install reading). Adjust fan speed or add second suction point for sub-2.0 result. |
EPA threshold mapping
EPA Action Level: 4.0 pCi/L (148 Bq/m³). WHO Action Level: 2.7 pCi/L (100 Bq/m³, more conservative). Conversion: 1 pCi/L ≈ 37 Bq/m³. Sources: EPA Citizen's Guide to Radon (EPA 402/K-12/002), WHO Handbook on Indoor Radon (2009).
How Radon Test Results Map to EPA Action Levels
The EPA publishes a single binary action threshold (4.0 pCi/L), but the actual risk gradient is continuous. Here's the full EPA + WHO threshold structure with the recommended response at each tier.
| pCi/L reading | Bq/m³ equivalent | EPA / WHO classification | Recommended action |
|---|---|---|---|
| 0.0 – 1.0 | 0 – 37 | Below US national average (1.3 pCi/L) | No action. Re-test every 2 years. |
| 1.0 – 2.0 | 37 – 74 | Average household range | No action. Re-test every 2 years. |
| 2.0 – 2.7 | 74 – 100 | EPA "consider mitigating" / WHO action level | Consider mitigation. Re-test with long-term (90+ day) protocol. |
| 2.7 – 3.9 | 100 – 144 | EPA "consider mitigating" zone | Mitigation recommended if smokers, children, or basement bedrooms present. |
| 4.0 – 9.9 | 148 – 366 | EPA Action Level — fix the home | Install active radon mitigation system as soon as practical. |
| 10.0 – 19.9 | 370 – 736 | High exposure zone | Urgent mitigation. Consider interim ventilation while install is scheduled. |
| 20.0 – 99.9 | 740 – 3,696 | Very high exposure zone | Mitigation is urgent. Limit time in affected lower levels until system is installed. |
| 100+ | 3,700+ | Extreme exposure — historical equivalents include EPA radon survey (~2,700) and uranium-mine occupational levels | Emergency mitigation. Vacate affected lower levels of the home until mitigation completes and verification confirms below action level. |
Test method comparison
EPA, AARST, and NRPP all explicitly endorse charcoal canisters, CRMs, and alpha-track detectors as the three primary protocol-grade test methods. Consumer-grade monitors are useful for trending but are not accepted for go/no-go threshold decisions.
Which Radon Test Method Is Right for Your Situation?
Three EPA-approved test method families — each with different best-use cases, accuracy bands, and turnaround.
| Method | Duration | Cost | Best use case | Limitations |
|---|---|---|---|---|
| Charcoal canister (short-term) | 48-96 hours | $15-30 | Initial screening, real estate transactions, post-mitigation verification | Sensitive to humidity; must be lab-processed; one-shot measurement |
| Continuous radon monitor (CRM) | 48-96 hours | $100-200 rental + lab | Real estate transactions (preferred), post-mitigation verification, tamper-evident | Higher cost; requires AARST-NRPP-certified provider |
| Alpha-track detector (long-term) | 90+ days | $25-50 | Confirming short-term result; assessing chronic exposure; whole-year average | Cannot be used for transaction timelines; mail-in lab processing |
| Electret ion chamber | 2-90 days | $30-100 | Versatile short- or long-term option | Limited US availability post-2020 |
| Consumer digital monitor (Airthings, Corentium, Ecosense) | Continuous, real-time | $150-300 device | Ongoing trend monitoring; awareness; post-mitigation reassurance | Not accepted for real estate or lender documentation; ±20% calibration tolerance |
EPA-aligned decision flow
You Have a Radon Test Result — Now What?
Step 1 — Validate the result
Was the test done under closed-house conditions? Was the kit exposed within the proper 48-96 hour window? Was the device placed correctly (3+ ft from exterior walls, 1+ ft above floor)? If any answer is no, the result is unreliable — re-test.
Step 2 — Map to EPA action level
Use the calculator above or the threshold mapping table. Reading 4.0 pCi/L or higher → mitigation. Reading 2.0-3.9 pCi/L → consider mitigation. Reading <2.0 → no action.
Step 3 — Confirm with second test
EPA recommends following up an elevated short-term test with either a second short-term test or a long-term (90+ day) test for confirmation — except when transaction timelines require immediate action.
Step 4 — If mitigation is recommended, route to certified contractor
All radon mitigation work in Ohio must be performed by an NRPP- or NRSB-certified contractor with ODH state credentials per Ohio Admin. Code Chapter 3701-69 (Ohio Radon Licensing Act). Call (614) 259-7858 for routing to a verified partner.
Step 5 — Post-mitigation verification
Within 30 days of system activation, perform a 48-96 hour CRM or short-term canister verification test to confirm the home is below 4 pCi/L. Re-test every 2 years thereafter to confirm continued system performance.
Radon test results FAQ
Common Radon Test Result Questions
Frequently Asked Questions
My radon test reads exactly 4.0 pCi/L — does that count as elevated?
Yes. The EPA action level is 4.0 pCi/L, and any reading "at or above" 4.0 triggers the EPA recommendation to fix the home. A reading of exactly 4.0 is in the action zone. EPA also recommends "considering" mitigation in the 2.0-3.9 pCi/L range, so a 4.0 reading is unambiguously in the act-now category — particularly if you have smokers, children, or bedrooms in lower levels.
My short-term test came back high but a long-term test came back low — which do I trust?
Long-term tests (90+ days) are more accurate for assessing chronic exposure risk because they average out short-term variations driven by weather, ventilation, and stack effect. EPA generally recommends following up an elevated short-term test with a long-term test for confirmation. However, if your short-term test was 4.0 pCi/L or higher AND a long-term test came back below 4 pCi/L, you still have at least one measurement showing elevated levels — re-test with a third measurement (ideally another long-term test) or err on the side of mitigation if the short-term reading was substantially above 4.0.
My charcoal canister was open longer than 96 hours — is the result valid?
No. Charcoal canisters lose accuracy when exposed longer than 96 hours (or shorter than 48 hours). Charcoal continuously adsorbs and de-adsorbs radon, and beyond the 48-96 hour window, the lab calculation cannot accurately reverse-engineer the actual radon level. Discard the canister and purchase a fresh kit. Most national testing labs (Air Chek, RTCA, Alpha Energy, etc.) flag canisters tested outside this window and refuse to issue a result.
My continuous radon monitor (CRM) showed a huge spike during a rainstorm — should I be worried?
Rainstorm spikes are real but usually transient. Falling barometric pressure during a storm pulls radon up through the soil into the home at a higher rate than calm-weather days. Most CRMs will show a 2-5x increase during a storm. For real estate transaction decisions, EPA closed-house protocol requires testing during stable weather. For lifetime-exposure decisions, look at the test's 48-96 hour AVERAGE — not the peak. If your 48-hour average is above 4.0 pCi/L even with the storm included, mitigation is still recommended.
My test result is exactly 2.0 pCi/L — do I need mitigation?
2.0 pCi/L sits at the lower end of EPA's "consider mitigation" zone (2.0-3.9 pCi/L). EPA does not require mitigation at this level but recommends considering it, especially if you have: (1) smokers in the household (radon multiplies smoking-related lung cancer risk ~9x), (2) children, (3) bedrooms in lower levels, or (4) confirmed elevated readings in neighbor homes. The WHO action level is 2.7 pCi/L — more conservative than EPA. At 2.0, plan to re-test in 2 years or after any major foundation work.
My basement reads 8.0 pCi/L but my first-floor reads 2.0 — which level matters?
Both, but the basement reading is the priority. EPA protocol for testing is to measure in the lowest occupied (or potentially occupied) level of the home — typically the basement if it's finished or used for any living space. If your basement is finished and used as a family room, bedroom, office, or playroom, the 8.0 pCi/L reading is the actionable number. If the basement is unfinished and you never spend time there, the first-floor reading is more representative of your actual exposure — but mitigation still significantly reduces both readings simultaneously.
Why did my radon level change when I closed the windows for testing?
Closed-house conditions (windows shut for 12+ hours before and during testing) are EPA-required because open windows artificially dilute indoor radon. The test is supposed to measure radon as it actually accumulates in the home during typical occupied conditions — most US homes are closed-up during winter heating and summer AC seasons. An open-window radon test will read substantially lower than the home's true winter or summer occupancy concentration. Always re-test under closed-house protocol if your original test conditions were not controlled.
My alpha-track detector took 90 days to deliver a result — is that normal?
Yes. Alpha-track detectors are LONG-TERM tests designed to measure radon over 90 days or longer. They cannot be read in real time — they must be mailed to the lab for chip etching and microscope analysis. The lab typically returns a result 2-3 weeks after receiving the device. Alpha-track tests are more accurate than short-term charcoal canisters for measuring chronic exposure but cannot be used for real estate transaction timelines.
Can dust or humidity affect a radon test result?
Yes — particularly for charcoal canisters. Charcoal canisters should be placed away from drafts, moisture sources, exterior walls, and fans. High humidity (>80% relative) can saturate the charcoal and skew results downward. Excessive dust can block the canister's exposure surface. Continuous radon monitors (CRMs) are less sensitive to humidity but should still be placed 3+ feet from exterior walls, 1+ foot above floor level, and away from windows, doors, and HVAC supply vents.
I tested with a digital home monitor (Airthings, Corentium) — should I re-test with a professional kit?
Consumer-grade digital monitors (Airthings View Radon, Corentium Home, Ecosense RD200) are useful for ongoing trend monitoring but are NOT acceptable for: (1) real estate transactions, (2) lender documentation, (3) post-mitigation verification, or (4) initial determination of whether to mitigate. For those decisions, use an EPA-protocol short-term test (48-96 hour charcoal or CRM from a certified lab) or AARST-NRPP-certified continuous monitor. Consumer monitors typically have ±20% accuracy bands — fine for trending but not for go/no-go decisions at the 4.0 pCi/L threshold.
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