While the test is running
A radon test in progress needs almost nothing from you except consistency. The failures are all things that get done accidentally.
If the house is being shown or occupied by anyone who has not read the preparation checklist, this is the page to hand them.
Maintain throughout
Keep exterior windows and doors closed except for normal entry and exit — hard to reverse later
The condition applies for the whole measurement, not just the twelve hours before it.
Keep whole-house fans, attic fans, window units, and evaporative coolers off — hard to reverse later
A single overnight run can invalidate the measurement.
Leave the device exactly where it was placed — hard to reverse later
Moving it makes the result incomparable to any before-or-after measurement.
Do not cover the device, put anything on it, or move furniture against it
Restricted airflow around the device measures the obstruction rather than the room.
If the house is being shown
Brief the listing agent in writing before the first showing — hard to reverse later
Agents open windows to air out a house. It is a reasonable instinct and it will cost you the test.
Put a note beside the device asking that it not be moved
A visitor who does not know what it is will move it to look at something.
Ask that showings avoid propping exterior doors
Normal entry and exit is fine; a propped door is deliberate ventilation.
Note anything unusual
Record any breach of conditions, even a small one — hard to reverse later
A test you know was compromised is worth re-running. A test you suspect was compromised and cannot document is an argument.
Record a severe storm, high wind, or heavy rain during the test
These conditions raise readings, and noting them helps interpret an unusually high result.
Record a power failure affecting HVAC or a running mitigation fan — hard to reverse later
If a mitigation system was off during part of the test, the result does not describe the mitigated house.
At the end
Do not collect the device early — hard to reverse later
A short test ended before its stated duration is not a valid short-term measurement.
Seal and post a passive kit promptly — hard to reverse later
Delay between exposure and analysis introduces error, and kits have shelf-life limits.
Photograph the device in position before removing it
Documents the placement, which matters if the result is later disputed.
What this checklist does not cover
A checklist that pretends to be complete is worse than one that states its edges. These are the things deliberately left out, each with somewhere better to go:
- This checklist assumes the preparation checklist was followed. If conditions were not established beforehand, the measurement is already compromised.
- It does not cover interpreting the result. That is the result interpreter.
- It does not cover post-mitigation verification specifically, though the same conditions apply.
Confidence and limits of this page
Every decision resource on this platform states its own boundaries. This is not a disclaimer — it is the part of this checklist you should read before relying on it.
- What we knowClaims on this page we stand behind, each traceable to an approved source or to observable structure.
- Closed-building conditions apply throughout the measurement, not only before it. That is protocol, not our preference.
- A test ended before its stated duration is not a valid short-term measurement.
- Severe storms and high winds raise indoor readings, which is why guidance advises against testing during them.
- What we do not knowQuestions you may reasonably have that this page does not answer.
- How often transaction tests are actually invalidated, and by which specific breach. This is described as common by practitioners and is nowhere measured.
- Whether a breach you did not notice occurred. A passive kit cannot tell you; a continuous monitor’s log can.
- What research would settle itWhat it would actually take to answer the above — naming it is the difference between honesty and hedging.
- A study of transaction-test invalidation rates by cause would let this checklist rank its critical items by real frequency rather than by our judgement of severity.
- Paired passive-kit and continuous-monitor deployments in occupied, actively marketed homes would quantify how often conditions silently fail.
- What we do not claimClaims you might expect to find here and will not, with the reason.
- We do not claim a compromised test always reads low. Ventilation usually pushes readings down, but a specific breach in a specific house can do otherwise.
- We do not claim this list is exhaustive. It covers the failures we can describe, not every possible one.
- What we cannot independently verifyFacts this page relies on that we could not confirm ourselves.
- Whether conditions actually held in your house. Only a continuous monitor with a log can evidence that, which is why transactions favour them.
Sources
- U.S. EPA — Radon
- U.S. EPA — A Citizen’s Guide to Radon
- U.S. EPA — Home Buyer’s and Seller’s Guide to Radon
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