During a short-term radon test, keep windows closed throughout the home and use exterior doors only for normal entry and exit. Long-term testing is different: it generally measures the home under normal living conditions, including ordinary window use. Check the instructions for your particular test before changing ventilation.
If a window was left open, record what happened and contact the laboratory or tester. They need that information to determine the next step.
First, identify the test you are taking
Find the device name, required test duration and instructions supplied by the laboratory or measurement professional. Also check whether the test is for a home sale, which can involve additional state or testing requirements. The Minnesota Department of Health’s testing guide, for example, distinguishes typical short-term screening from longer measurements and recommends a licensed professional when an independent real-estate test is needed.
Use the specified start and finish times. A device’s appearance does not tell you which procedure applies. For example, AccuStar’s liquid-scintillation instructions specify 48–96 hours, with a shorter maximum where high humidity is unavoidable, while its alpha-track instructions specify 91–365 days. Those are examples for those products, not interchangeable schedules.
For a broader look at choosing a test for a particular concern, see our guide to targeted indoor air testing.
What closed-house conditions mean
For a short-term test, keep windows closed throughout the house, including rooms away from the detector. Exterior doors can open briefly as people enter or leave; avoid propping them open to ventilate. You can continue living in the home.
AccuStar’s test instructions FAQ specifically includes attic and basement windows. Closing only the room containing the detector does not meet those instructions.
Prepare before the measurement starts. The EPA Home Buyer’s and Seller’s Guide to Radon, printed page 20, calls for at least 12 hours of closed-house conditions before a 2–4-day test and throughout the test. Follow your laboratory’s preparation period and applicable protocol rather than treating either 12 or 24 hours as a rule for every kind of air test.
Can heating, air conditioning and fans stay on?
Do not assume every system that moves air has the same testing instructions. Heating or cooling that recirculates indoor air differs from equipment that exchanges air with outdoors.
For example, AccuStar’s liquid-scintillation procedure specifies HVAC on Auto, window air conditioners set to recirculate, and no whole-house exhaust-fan operation. It permits dehumidifiers and says to keep the radon mitigation system operating.
Kitchen and bathroom exhaust fans need a specific answer from your tester. EPA’s checklist permits small exhaust fans for brief periods, but Michigan EGLE’s short-term testing guidance says kitchen and bathroom fans should be off. Ask which instructions apply to your test before it begins.
If your home has an HRV, ERV, outdoor-air intake, continuously operating exhaust system or unfamiliar controls, tell the tester what is installed. Ask for written operating instructions instead of guessing which switch to change. Do not disconnect equipment or block vents on your own to create testing conditions.
A radon mitigation fan has a different job from a whole-house ventilation fan. EPA’s checklist, printed page 21, says an existing active radon-reduction system should be working properly and remain operating during the test.
Can you open windows during a long-term radon test?
Generally, yes, as part of the way you normally use the home. Michigan EGLE describes year-long alpha-track testing under normal living conditions, including ordinary use of windows, doors and mechanical ventilation.
The aim is to measure the home as you live in it across changing conditions. Do not deliberately air out the house to influence the result. Follow the device’s placement and duration instructions, and ask the lab about unusual changes such as construction or an extended vacancy.
Do not convert a short-term test into a long-term test simply by leaving it out longer. Devices have their own permitted exposure periods.
What if someone opened a window during the test?
For a test requiring closed-house conditions, close the window if it is safe to do so and make a factual record:
- Which window or exterior door was open and where it is in the house.
- When it opened and closed, or your best estimate if you are unsure.
- Any change in ventilation equipment, power, or detector location.
- The device identification and the test’s scheduled start and finish times.
Contact the laboratory or tester promptly. Ask whether to continue as scheduled, restart with a new device, or arrange another measurement. Leave the detector undisturbed and follow their instructions about ending and returning it.
Do not declare the result valid or invalid from the window opening alone, subtract selected hours, apply a correction factor, or extend the exposure yourself. EPA warns that interference with testing conditions can affect results and may require another test. The appropriate response depends on the device and protocol.
For a real-estate test, report the deviation to the measurement professional so it can be documented in the testing record. EPA’s real-estate checklist advises another test if the seller or qualified tester cannot confirm that all checklist requirements were met.
A short checklist before you begin
- Confirm: Device, test purpose, preparation period, exposure duration and the applicable household instructions.
- Plan: Tell everyone in the home when the test starts and finishes, and clarify window, door and equipment use.
- Record: Keep the device number, instructions, start and finish times, and any departures from the plan.
- Finish: End and return the test exactly as instructed. Keep the report and follow its recommended next steps.
These are practical planning prompts, not a substitute for your test protocol. If you cannot maintain the required conditions safely, contact the tester about another testing plan.
