Regulatory Framework
EPA MAH-2023 Protocol
4.0 pCi/L (148 Bq/m³)
Tamper-evident placement, closed-building conditions for 12 hours before and during test, minimum 48-hour duration for continuous monitors or 2-7 days for passive detectors.
AARST Standards (ANSI/AARST MAH-2014, updated 2023)
4.0 pCi/L action level
Certified measurement devices, documented chain of custody, interference-free placement 20 inches from exterior walls.
Testing Protocols
Short-term Continuous Monitor Test (48-96 hours)
Duration: 2-4 days
- •Use EPA-approved continuous radon monitor with ±25% accuracy
- •Place in lowest livable level, 20+ inches from walls
- •Maintain closed-building conditions 12 hours before and during test
- •Provide tamper-evident seals on windows/doors
- •Document environmental conditions and device placement
Passive Detector Test (2-7 days)
Duration: 2-7 days
- •Use NRPP or NRSB-listed activated charcoal canister or electret
- •Laboratory analysis within 5 days of exposure end
- •Duplicate detectors in 10% of tests for QA
- •Proper documentation of exposure start/end times
Recommended Equipment
Preferred for Real Estate (speed + reliability)
Continuous monitors provide 48-hour results with hourly data, allowing detection of tampering and compliance verification. Essential for transaction deadlines.
Budget Alternative (slower turnaround)
Passive detectors cost less but require laboratory analysis (5-7 days total). Acceptable if transaction timeline allows delay.
Protocol Requirements
Real estate radon testing follows the EPA MAH-2023 protocol, designed for time-sensitive transactions. The protocol balances speed with accuracy, requiring minimum 48 hours of closed-building conditions to capture representative radon levels while meeting typical inspection deadlines.
Closed-Building Conditions
All exterior windows and doors must remain closed 12 hours before test start and throughout the measurement period. Exception: normal entry/exit through doors. HVAC systems should operate normally. Fans or air purifiers that create continuous air exchange with outdoors should be turned off.
Placement Requirements
Test in the lowest livable level of the home. Place device 20+ inches from exterior walls, 3+ feet from heating/cooling vents, and at least 20 inches above floor. Avoid kitchens, bathrooms, and laundry rooms due to humidity and ventilation interference.
Duration and Timing
Minimum 48 hours for continuous monitors. Passive detectors typically run 2-7 days. Longer durations provide more accurate annual average estimates. Tests conducted during heating season (October-April in northern climates) typically show higher readings than summer tests.
Decision Rules and Action Levels
The EPA action level is 4.0 pCi/L (148 Bq/m³). If a short-term test shows 4 pCi/L or higher, the EPA recommends taking action to reduce radon. For results between 2-4 pCi/L, consider a follow-up test or radon-reduction measures. Results below 2 pCi/L are acceptable, though no radon level is entirely safe.
Negotiation Thresholds
Buyers typically request mitigation systems for results ≥4.0 pCi/L. Some contracts include contingencies for results as low as 2.0 pCi/L. Sellers may offer to install mitigation systems or provide credits. Post-mitigation retests should show levels below 2.0 pCi/L to confirm system effectiveness.
Post-Mitigation Verification
After mitigation system installation, conduct a 24-48 hour verification test using a continuous monitor. Test should occur at least 24 hours after system activation, with closed-building conditions. Most systems reduce radon by 80-99%, achieving final levels of 0.5-2.0 pCi/L.
Cost and Logistics
Professional radon testing for real estate typically costs $150-$250, included in standard home inspection packages or ordered separately. DIY testing with passive detectors costs $15-$50 but requires 7-10 days total (exposure + lab analysis). Continuous monitor rentals cost $100-$200 for professional-grade devices with faster 2-day results.
Who Pays for Testing?
Buyers typically pay for radon testing as part of their due diligence. In some markets, sellers provide pre-listing radon tests to address concerns upfront. Mitigation costs ($800-$2,500) are negotiable and often split or credited at closing if high levels are discovered.
Timeline Considerations
Short-term tests fit within typical 7-10 day inspection periods. Order tests immediately after offer acceptance. Continuous monitors provide results in 2-4 days. Passive detectors take 7-10 days (2-7 day exposure + 2-5 day lab turnaround). Plan for potential mitigation and retest, adding 7-14 days to the timeline.
Frequently Asked Questions
Can I use a consumer-grade monitor (like Airthings View Plus) for real estate transactions?
It depends on your state and contract requirements. Some states require EPA-listed or NRPP-certified devices, which exclude most consumer monitors. Professional-grade continuous monitors (Corentium Pro, Sun Nuclear 1028) are widely accepted. Check your purchase agreement and local regulations before relying on consumer devices for binding test results.
What if the seller refuses to fix high radon levels?
Options include: (1) negotiate a price reduction to cover mitigation costs ($800-$2,500), (2) request seller install system before closing, (3) walk away if contract has a radon contingency, or (4) accept the risk and install mitigation after purchase. Most radon-reduction systems are straightforward to install post-closing, so price adjustments are common.
Do I need to retest every time I buy or sell a home?
Yes. Radon levels vary significantly between neighboring homes due to soil geology, construction type, and foundation condition. A previous test at the same address may not represent current conditions, especially if renovations occurred or the mitigation system was removed or failed. Always conduct a new test during the transaction period.