The EPA’s radon testing protocols are the foundation for nearly every state radon program, real estate testing standard, and measurement professional certification in the United States. Understanding what the EPA actually requires — not what a neighbor summarizes or a contractor implies — lets you evaluate whether your testing was conducted correctly and whether your results are defensible.
EPA Radon Testing Guidance: Overview
The EPA’s primary radon testing guidance documents for homeowners are the A Citizen’s Guide to Radon and the Home Buyer’s and Seller’s Guide to Radon. For measurement professionals, the EPA Radon Measurement Proficiency Program established the original certification framework that NRPP and NRSB now administer. AARST-ANSI measurement standards (MAMF, ANSI/AARST Series) build on EPA guidance and are the operative standards for professional measurement.
Closed-House Conditions: The Core Protocol Requirement
Closed-house conditions are the most important and most frequently violated component of EPA’s short-term testing protocol. Without closed-house conditions, short-term results are not comparable to the EPA action level and may significantly underestimate actual radon levels.
What Closed-House Conditions Mean
- Keep all windows and exterior doors closed during the test and for 12 hours before the test device is placed
- Do not operate whole-house fans, attic fans, or similar ventilation during the test or the 12-hour pre-test period
- Normal HVAC operation is permitted — heating and cooling systems that recirculate interior air (central HVAC) may run normally
- Ceiling fans: permitted
- Kitchen and bathroom exhaust fans: minimize use; brief operation for cooking or showering is acceptable, but extended operation creates pressure differential
- Fireplace dampers: keep closed if not in use; do not operate fireplaces during the test
Why Closed-House Conditions Matter
Open windows introduce large volumes of outdoor air (~0.4 pCi/L radon) that dilute indoor radon levels to artificially low values. A home with actual indoor radon of 8.0 pCi/L may test at 3.0–4.0 pCi/L with windows routinely open — below the action level, creating a false impression of safety. This is why summer testing with open windows is unreliable and why EPA requires closed-house conditions for short-term tests.
Device Placement Protocol
EPA’s placement requirements for radon test devices:
- Level: Lowest level that is used or could be used as living space — including unfinished basements if they could be finished, and basements where family members spend any time regularly
- Height: At least 20 inches above the floor, within the breathing zone
- Wall distance: At least 12 inches from any wall
- Avoid: Drafts from windows, doors, HVAC supply/return vents, exterior walls; direct sunlight; humidity sources (sump pits, laundry, showers)
- Do not place in: Kitchens, bathrooms, crawl spaces, or closets
- Placement in room: Central to the room is ideal; near where occupants typically spend time is the goal — not in an uninhabited corner
EPA’s Two-Test Decision Protocol
For initial testing of a home, EPA’s protocol is designed to balance speed against accuracy:
If Initial Short-Term Test is Below 4.0 pCi/L
No immediate action required. Retest in 2 years. If the result was between 2.0 and 3.9 pCi/L, consider a long-term test to confirm the annual average. Levels in this range may be higher during different seasons or weather conditions.
If Initial Short-Term Test is 4.0–7.9 pCi/L
Follow up with either a second short-term test or a long-term test before making a mitigation decision. The rationale: a single 48-hour test in this range has sufficient measurement uncertainty that a confirmatory test substantially improves confidence in the true annual average level. If the confirmatory test also comes in at or above 4.0 pCi/L, mitigate. Average the two short-term results if using two short-term tests.
If Initial Short-Term Test is 8.0 pCi/L or Higher
EPA recommends proceeding to mitigation without waiting for a confirmatory test. At this concentration, the risk from continued exposure during a second test period is not justified by the additional certainty. Contact a certified radon mitigator and schedule installation.
The 4.0 pCi/L Action Level: Context and Criticism
EPA’s 4.0 pCi/L action level was established in the 1980s based on risk assessments available at the time and the practical cost of mitigation. It has not been formally revised since, despite significant advances in radon health research.
Notable context:
- The World Health Organization reference level is 2.7 pCi/L (100 Bq/m³) — lower than EPA’s threshold
- EPA itself notes that “radon levels less than 4 pCi/L still pose a risk, and in many cases may be reduced” — the 4.0 level is an action threshold, not a safety threshold
- EPA’s own long-term goal is to reduce indoor radon to outdoor air levels (0.4 pCi/L), acknowledging that any indoor radon above background carries some risk
- Several European countries have adopted national reference levels of 1.4–2.7 pCi/L (50–100 Bq/m³)
For practical purposes: the 4.0 pCi/L threshold determines when EPA recommends mandatory action. Below 4.0 pCi/L, mitigation is EPA-recommended for consideration between 2.0–3.9 pCi/L and is always a personal risk decision.
EPA Guidance on Specific Testing Situations
Real Estate Transactions
EPA recommends testing in real estate transactions. When time is limited (common in transaction timelines), short-term tests are acceptable. EPA provides guidance that real estate tests should follow closed-house protocols strictly and that buyers should understand the limitations of a single 48-hour test relative to annual average exposure.
Post-Mitigation Testing
EPA recommends testing 24+ hours after system activation (if continuous monitor) or placing a charcoal canister at least 24 hours post-activation for a minimum 48-hour test. If results are still at or above 4.0 pCi/L, contact the mitigator — the system requires adjustment.
New Construction (RRNC)
EPA recommends testing new homes with RRNC passive systems after at least 60 days of occupancy, under normal living conditions (closed-house protocol not required for this application — the extended occupancy averages conditions sufficiently). If results are at or above 4.0 pCi/L, activate the passive system with a fan.
Frequently Asked Questions
What is EPA’s recommended radon action level?
EPA’s action level is 4.0 pCi/L — the concentration at which EPA recommends mitigation. EPA also recommends considering mitigation at 2.0–3.9 pCi/L, acknowledging that radon at those levels still poses meaningful cumulative health risk, particularly for households with smokers or young children.
Does EPA require professional radon testing?
EPA does not federally mandate professional testing for homeowners conducting their own radon assessments. DIY test kits from NRPP- or NRSB-certified labs are EPA-endorsed for homeowner use. Professional certified testing is required for real estate transactions in some states, for regulatory compliance contexts, and when chain-of-custody documentation is needed.
What is the difference between EPA and WHO radon action levels?
EPA’s action level is 4.0 pCi/L (148 Bq/m³). The WHO reference level is 2.7 pCi/L (100 Bq/m³). The WHO level reflects more recent health evidence and is lower. In practice, both acknowledge significant risk below their respective thresholds — the difference is where each organization draws the line for recommended action.
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