Testing conditions · source-linked
Radon Closed-House Conditions
Use this 12-hour closed-house checklist for a 2–4 day real-estate radon test: windows, exterior doors, fans, HVAC, and test timing.
Direct answer
For a 2–4 day real-estate test, close windows and begin closed-house conditions at least 12 hours before the test. Keep exterior doors closed except for normal entry and exit, and do not run equipment that brings in outdoor air.
Reviewed September 5, 2026. United States federal guidance. Device instructions and applicable state requirements take precedence.
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Built from the official primary guidance linked on this page.
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Reviewed September 5, 2026 · maintained by RadonVerdict.
What “closed house” actually means
The house does not need to be vacant or sealed against normal entry. EPA's definition allows ordinary entry and exit. The condition is about avoiding deliberate outdoor-air exchange that changes the test environment.
Heating and cooling can operate normally. For a transaction test lasting less than one week, EPA says only air-conditioning units that recirculate indoor air should operate.
For 2–4 day transaction tests, start 12 hours early
EPA's real-estate checklist says to maintain closed-house conditions for at least 12 hours before a 2–4 day short-term test begins and throughout the test. For 4–7 day transaction tests, EPA recommends maintaining the conditions.
Because our planner asks only whether the condition was followed, it cannot verify each window, fan, or timestamp. Record any uncertainty rather than converting it into a clean pass.
Keep conditions steady during the test
Do not open windows for ventilation or run equipment that brings in outside air. Do not disturb the device. If an active radon-reduction system is already installed, EPA says it should operate properly throughout the test.
A brief normal door opening is not the same as leaving a door open. Write down any event that may matter so a tester or laboratory can review it.
This page does not create a universal legal rule
The cited checklist was written for home purchases and sales. Device instructions, state requirements, and professional standards may be more specific and can control the test.
For a routine home test, read the kit's conditions first. RadonVerdict does not infer state law from the federal guide.
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Check only what you can confirm. The summary keeps unresolved items visible instead of converting uncertainty into a pass.
Open the full test plannerCommon questions
Quick answers
Can I open the door during a radon test?
EPA's closed-house definition permits normal entry and exit. It does not support leaving exterior doors open for ventilation.
Can the air conditioner run?
EPA's transaction guide says normal heating and cooling may operate; for tests under one week, air-conditioning should recirculate indoor air rather than bring in outside air.
What if a window was opened?
Record what happened and for how long, then check the device or laboratory instructions. For a transaction test, the protocol may need professional review or another test.
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