Short-term tests are usually 2 to 7 days long and are done under "closed-house" conditions. Closed house conditions mean that the house is closed up for at least 12 hours before the test and for the duration of the test.
- Exterior windows and doors are kept shut, except for normal entrance and exit.
- Fans and blowers which move air from the outside of the house to the inside, or exhaust inside air to the outside, are turned off, including swamp coolers.
- Whole house fans should be off.
- Air conditioners should be put on “recycle" or "max.-cool," but not on the "fresh air" setting.
- Combustion or makeup air to gas fired appliances are NOT to be closed.
The house can be occupied during testing, provided the "closed house" conditions described above are maintained.
If testing during warm weather, keep the air-conditioning on and set the fan to recycle indoor air. Do not use the "fresh air" setting. Evaporative coolers, sometimes called "swamp coolers" should be turned off during the test to avoid bringing outdoor air into the house.
Short-term "closed house" radon tests should not be conducted during rainy weather, especially when the rain is accompanied by persistent winds. Changes in barometric pressure and other forces can cause indoor radon levels to rise during a rainstorm and skew the test results higher than found under otherwise normal conditions.
Note: Placing the test device in a closed room or leaving doors and windows open during the test is improper and can invalidate a test.