Windows were opened during the test
“It was warm, and the windows were open on and off for a couple of days.”
Closed-building conditions are the single most-cited requirement in radon testing, and open windows are the single most common departure from them. In an occupied house being lived in normally, it happens.
The effect is dilution, so the reading is likely to understate the house. That direction is the useful part.
Why this matters
What it changes about the decision in front of you.
- Ventilation exchanges indoor air with outdoor air, and outdoor concentrations are low, so the measured figure drops.
- The other side of a transaction will ask about this, and "we are not sure" is a materially weaker answer than "closed throughout".
What it could influence
Where the effect is likely to show, and in which direction where that is knowable.
- A result under a threshold might sit above it under closed conditions; that is the case where this matters most.
- The effect scales with how long and how widely the house was open, neither of which is usually recorded.
What this does not settle
What still stands. Noticing a problem is not the same as losing the evidence.
- A high reading in a ventilated house is a strong indication rather than a suspect one.
- The measurement happened and the device worked. Conditions are a describable, repeatable variable.
- It does not mean the household did something wrong — the requirement is genuinely inconvenient and is frequently not communicated well.
What a professional is likely to ask
Worth having answers ready. None of these is a test you can fail.
- Roughly how many of the test days involved open windows, and which parts of the house.
- Whether the household could realistically hold closed conditions for a repeat, and in what season.
- Whether a longer-duration device would suit the household better than repeating a short test.
What you can check yourself
Things you can establish today, without anyone visiting.
- Which windows were opened and roughly when, which most households can reconstruct.
- Whether the season makes closed conditions practical soon.
What genuinely needs somebody on site
Where this platform stops. These are not questions a website can answer about your house.
- How much the building actually exchanges air when open, which depends on layout and orientation.
Categories a next step could fall into
Unordered, and none of them is a recommendation. Which applies depends on things this page does not know about your situation.
Related reading
- How testing works — Devices, placement, closed-building conditions, and what invalidates a result.
- False positives — Most disputed results are not false — they are invalid, mismeasured, or comparing two different things.
Sources
- U.S. EPA — A Citizen’s Guide to Radon
When you are ready to talk to somebody
Tell us about your home and what you are trying to work out. We will tell you honestly whether we can route it to a provider in your area today.