The device was near a window or an exterior door
“I have realised the kit was sitting on a windowsill, or right beside the back door.”
Placement guidance keeps devices away from openings for a straightforward reason: air near a door or window is partly outdoor air, and outdoor concentrations are low. A device there is measuring a blend.
That does not mean the reading tells you nothing. It means it probably understates the room rather than overstating it, which is the direction worth knowing before you decide anything.
Why this matters
What it changes about the decision in front of you.
- Air within a few feet of an opening exchanges with outside air far more than air in the middle of a room, so it is not representative of what occupants breathe.
- A result challenged in a transaction is challenged on placement more often than on the device, and a windowsill is the easiest challenge to make.
What it could influence
Where the effect is likely to show, and in which direction where that is knowable.
- The reading is likely to sit lower than a compliant placement in the same room would have produced, though by how much nobody can say.
- If the opening was used during the test, the effect will be larger and more variable than if it stayed shut throughout.
What this does not settle
What still stands. Noticing a problem is not the same as losing the evidence.
- A result above the action level from a diluted position is still a result above the action level, and arguably a stronger signal than the same figure from mid-room.
- The measurement still establishes that measurable levels are present in that space, which is more than an untested house knows.
- It does not follow that every other reading in the house is wrong, or that the device malfunctioned.
What a professional is likely to ask
Worth having answers ready. None of these is a test you can fail.
- How far the device sat from the opening, and whether the opening was used during the test period.
- Whether the room has other placement options that would meet the distance guidance.
- Whether anyone recorded the placement at the time, or it is being reconstructed now.
What you can check yourself
Things you can establish today, without anyone visiting.
- The distance from the device position to the nearest opening, which you can measure now with a tape.
- Whether that door or window is one the household actually uses day to day.
What genuinely needs somebody on site
Where this platform stops. These are not questions a website can answer about your house.
- Whether the room has a compliant placement position at all, which depends on the layout and the furniture.
- How much air movement that opening actually produces under normal operation of the house.
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
- U.S. EPA — 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.