Continuous Radon Monitors (CRM) are testing devices favored by many home inspectors. CRM's offer some distinct advantages over passive testing devices like charcoal canisters. A trained operator can often tell if someone had opened windows during the test, if the device was moved, or if things like furnace & laundry operation are impacting indoor radon concentrations.
For all the tangible benefits CRM's offer, there are some things to beware of when these devices are deployed for screening measurements in real estate transactions . Probably most importantly; misinterpretation of results. The graph below is a test result of a recently deployed Continuous Radon Monitor in a home that is on the market. If you look closely, the overall average radon concentration for the testing period was 7.6 pCi/l. The buyer of this property was "alarmed" because the graph showed spikes in radon levels as high as 12.5 pCi/l, & dips as low as 2.7 pCi/l. The buyer was convinced that something was wrong.
As is evidenced by the graph, radon levels do fluctuate. Since it is heavier than air, radon entry into a home is predicated on pressure differentials...it is; "pressure Driven". Pressure differentials within a structure fluctuate continuously based on several climatic factors such as; rain, wind, snow, & temperature extremes. The presence or lack of any of these conditions will impact what happens to radon entry & therefore; radon concentrations within a structure. Peaks & valleys in a continuous radon monitor report should not automatically be interpreted as a sign of foul play or device error. Most often, they represent the true nature of radon entry.
Any type of "active" monitoring device should be calibrated at least annually. Don't be afraid to request a copy of the device's most recent calibration report. Big testing fees & elaborate reports are worthless if generated from an uncalibrated testing device.
If a constant "trend" in radon concentrations is recorded but highlighted with a brief (or extended) period of dramatically different results, ask the operator to investigate the source of the change. Was it a weather related anomaly?...The temporary use of a pressure altering device such as a wood stove or whole house attic fan?...or did someone open all the windows all of a sudden in hopes of influencing a lower result?
Continuous Radon Monitors can be a useful tool when trying to decipher whether or not a home has...or has the potential to have a radon problem. Realtors can be more confident of a CRM result when they are utilized in "questionable" locations.
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