Why Test for Radon
Radon is invisible, odorless, and tasteless. Testing is the only way to know if radon is present in your home at dangerous levels.
Testing for radon is simple, inexpensive, and takes only a few minutes of your time. Millions of homeowners worldwide have tested their homes for radon.
The amount of radon in the air is measured in becquerels per cubic meter (Bq/m³), which represents radioactive decay events per second. In the United States, an older unit called picocuries per liter (pCi/L) is sometimes used.
Types of Radon Tests
There are two general approaches to radon testing:
Short-Term Testing
Short-term tests remain in your home for 2 to 90 days, depending on the device.
Common short-term detectors:
- •Charcoal canisters
- •Alpha track detectors
- •Electret ion chambers
- •Continuous monitors
- •Charcoal liquid scintillation detectors
Advantages: Quick results, ideal when you need to make fast decisions (such as during real estate transactions).
Limitations: Radon levels vary day-to-day and season-to-season, so short-term tests are less likely to reflect your year-round average exposure.
Long-Term Testing
Long-term tests remain in your home for more than 90 days. Alpha track and electret detectors are commonly used for long-term testing.
Advantages: Provides a more accurate picture of your home's year-round average radon level.
Best for: Understanding true annual exposure, which is the most health-relevant measurement.
How to Use a Radon Test Kit
Follow the instructions included with your test kit. Most test kits follow similar protocols:
Test Placement
- •Location: Place the kit in the lowest lived-in level of your home (basement if frequently used, otherwise first floor)
- •Room selection: Choose a regularly used room (living room, bedroom, den, playroom) — not kitchen or bathroom
- •Height: Place at least 20 inches (50 cm) above the floor
- •Position: Keep away from drafts, high heat, high humidity, and exterior walls
- •Stability: Place where it won't be disturbed
Closed-House Conditions
For short-term tests:
- •Close all windows and exterior doors 12 hours before starting the test
- •Keep them closed during the entire test period
- •Normal entry and exit through doors is acceptable
- •Air conditioning and heating systems that recirculate indoor air may operate
- •Do not operate window fans or ventilation systems that bring in outdoor air
- •Small exhaust fans (bathroom, kitchen) running briefly are acceptable
- •Radon mitigation system fans should continue operating
Weather note: Avoid 2-3 day short-term tests during severe storms or unusually high winds.
After Testing
Once the testing period is complete:
1. Seal the test kit package according to instructions
2. Mail it to the specified laboratory immediately
3. Results typically arrive within 2-3 weeks
4. Save your results for future reference
Understanding Action Levels
International reference levels:
- •World Health Organization (WHO): Recommends mitigation at 100 Bq/m³
- •European Union: Recommends action at 300 Bq/m³
- •United States EPA: Recommends action at 148 Bq/m³ (4 pCi/L)
- •Canada: Recommends action at 200 Bq/m³
Important: No level of radon is completely safe. Even levels below these action thresholds carry some risk, though the risk increases substantially at higher concentrations.
Typical radon levels:
- •Outdoor air: ~15 Bq/m³ (0.4 pCi/L)
- •Average indoor level: ~48 Bq/m³ (1.3 pCi/L)
Many homes can be reduced to 74 Bq/m³ (2 pCi/L) or below with proper mitigation.
Recommended Testing Strategy
Step 1: Initial Test
Take a short-term test. If your result is 100 Bq/m³ (2.7 pCi/L) or higher, proceed to Step 2.
Step 2: Follow-Up Test
Choose one of these follow-up approaches:
- •Long-term test: For the most accurate year-round average
- •Second short-term test: If you need results quickly
The higher your initial result, the more urgent the follow-up. If your first short-term test shows levels more than double your local action level (e.g., above 300 Bq/m³ or 8 pCi/L if using US EPA guidelines), take a second short-term test immediately.
Step 3: Decide on Mitigation
- •If you used a long-term test: Consider mitigation if results are above your regional action level (typically 100-300 Bq/m³)
- •If you used two short-term tests: Consider mitigation if the average of both tests is above the action level
Alternative approach: For faster decision-making, you can conduct two short-term tests simultaneously (placed side-by-side, about 10 cm apart) and use their average.
Special Situations
Real Estate Transactions
When buying or selling a home, testing is often required or requested. Short-term testing is typically used due to time constraints. Consider:
- •Having tests conducted by an independent certified professional
- •Testing areas the buyer plans to use (finished basements, lower levels)
- •Providing existing test results to potential buyers
- •Fixing confirmed problems before listing the property
After Renovations
Major structural changes can affect radon levels. Always retest after:
- •Converting unfinished spaces to living areas
- •Finishing a basement
- •Major foundation work
- •Installing or modifying HVAC systems
Changing Use Patterns
Retest if you begin spending significant time in areas of your home that weren't previously tested (such as moving to a basement bedroom).
Test Result Interpretation
Your test results may not always be definitive, especially if close to action levels.
For example, if the average of two short-term tests is 110 Bq/m³, there's approximately a 50% chance your true year-round average is below 100 Bq/m³.
Recommendations based on results:
- •Below 100 Bq/m³: Risk is lower but not zero. Consider retesting every few years. Some health authorities recommend action even at this level.
- •100-300 Bq/m³: WHO recommends mitigation. Act within a reasonable timeframe (months, not years).
- •Above 300 Bq/m³: Take prompt action. High radon levels can be reduced by 90-99% with proper mitigation.
- •Very high levels (>1,000 Bq/m³): Seek immediate professional assessment and mitigation.
Even very high radon levels can be reduced to acceptable levels. Most homes can be fixed for costs comparable to common home repairs.
Finding Test Kits and Professionals
Test kits are available from:
- •Hardware stores and home improvement retailers
- •Online retailers
- •National radon programs and health authorities
- •Environmental health organizations
Professional testing services:
If you prefer professional testing, or if testing is required for real estate transactions, seek certified radon measurement professionals. Look for:
- •National or regional radon proficiency program certification
- •Professional liability insurance
- •Experience with your type of property
- •Independence from mitigation contractors (for unbiased results)
Contact your local environmental health authority or national radon program for lists of certified professionals in your area.
Related Guides
Source Attribution
This content incorporates material from U.S. Environmental Protection Agency publications, which are in the public domain. Content has been adapted for an international audience with unit conversions, translations to multiple languages, and global framing of concepts while preserving all scientific facts and health guidance.
This content is in the public domain under 17 U.S.C. § 105. Content has been adapted for an international audience and translated to multiple languages while preserving scientific accuracy.