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Testing Conditions

Radon test results can be affected.

Let’s face it, you can’t control the weather, and don’t blame the weather for your radon level.

It is true that weather conditions may effect your radon level. It is also true that no one can tell you for certain that bad weather will increase your radon level (it may reduce your radon level). That’s because every home is different.  Two identical style homes side by side built by the same builder at the same time are still going to have different radon levels, and the weather will affect each one differently.

Why? Its difficult to explain all the possible reasons but here is one simple explanation.

Wind blowing on the side of the first home will hit the second home differently, having different effects on radon levels inside of the identical homes.


As simple as the above explanation is the wind could very well cause one home to have a higher radon level than the other, but which home? and what about all the other factors effecting radon levels like how many times you open the front door or how many showers you take or how many loads of laundry you do etc. etc.

That’s why the minimum radon test takes 48 hours, so that there is an average result. Longer is better; longer testing does not mean the radon detector will read higher.

The following is Illinois Law regarding testing procedures, with the exception of some paperwork requirements it is the same as the EPA testing requirements.  Following these procedures does not mean your radon level will be higher.  Think of it as a standardization so two different test by different companies at different times will come up with something close to the same radon levels (reproducible results).

Section 422.130 Measurement Protocol (Illinois Law)

b) Measurements

1) A short-term measurement shall range in duration from 48 hours to 90 days, depending upon the measurement device used. Unoccupied homes shall be tested with the HVAC system set and operating throughout the measurement interval in the normal range, such as 72 degrees F plus or minus 5 degrees F.

A) Short-term measurements shall be made under closed-building conditions. In measurements lasting more than seven days and less than 90 days, closed-house conditions shall be maintained as much as possible while the measurement is in progress.

B) Closed building conditions shall begin at least 12 hours prior to the beginning of the measurement period for measurements lasting less than 96 hours.

C) The following conditions shall be complied with during closed-building conditions:

i) Operation of permanently installed HVAC systems shall continue during closed-building conditions. Radon Measurement licensees shall inform the resident in writing that operation of dryers, range hoods, bathroom fans and other mechanical systems that draw air out of the building may adversely affect the measurement results.

ii) In buildings having permanently installed radon mitigation systems, the mitigation system shall be functioning during the measurement interval.

iii) Air conditioning systems that recycle interior air may be operated during closed-building conditions.

iv) All windows shall be kept closed.

v) All external doors shall be closed except for normal entry and exit. Structural openings due to disrepair or structural defects shall be repaired to correct their condition prior to initiation of closed-building conditions. All exterior windows and doors shall be inspected by a Radon Measurement Professional licensee or Radon Measurement Technician at the placement and retrieval of the detectors and the result of the inspection documented for the measurement file.

vi) Whole-house fans shall not be operated. Portable window fans shall be removed from the window or sealed in place. Window air conditioning units shall only be operated in a recirculating mode. If the building contains an air handling system, the air handling system shall not be set for continuous operation unless the air handling equipment is specifically used for radon control and is so labeled.

vii) Fireplaces or combustion appliances, except water heaters and cooking appliances, shall not be operated unless they are the primary sources of heat for the building.

viii) Ceiling fans, portable dehumidifiers, portable humidifiers, portable air filters and window air conditioners shall not be operated within 20 feet of the detector.

D) Short-term measurements of less than 96 hours shall not be conducted during severe storms or periods of sustained high winds (30 miles per hour or more). Radon Measurement licensees shall check and document local weather forecasts prior to placing short-term measurement devices when the measurement period is less than 96 hours.

AGENCY NOTE: The National Weather Service defines a severe storm as a storm that generates winds of 58 mph and/or ¾-inch diameter hail and that may produce tornadoes – not necessarily in that order.