Factors that affect the accuracy of a Radon Test
Bottom Line: Air Pressure and the duration of the Radon test.
A radon test is meant to provide an average of radon concentration over a period of time. The radon concentrations will fluctuate daily and seasonally, but a radon test is meant to give the occupant an idea of what radon levels they are exposed to over the course of a year.
Air Pressure. Since radon is coming from the bedrock, crawlspace, foundation of your home then any thing that would cause more air to come into your home from below due to pressure differentials could impact the accuracy of your Radon test.
How might changes in air pressure occur? Air Pressure in a home can fluctuate based off of natural events like major weather systems and high winds. Air Pressure will also fluctuate from “man-made” factors like the type of HVAC systems within your home or if your doors/windows are open for extended periods of time. Think about when you open a window on one side of the house and an open door on the other side of the house slams shit. That’s a change in air pressure! All of these things affect the air pressure systems in and below your home and can affect the radon concentrations that are measured during a radon test.
Test Duration: Depending on the duration of the test, if one of these variables is present and spikes/lowers the amount of radon in the home at a given moment during the test it can greatly impact the accuracy of the radon test especially if it’s a short test, like 48 hours.
Using your typical Real Estate Transaction Radon Test as an example:
A Continuous Radon Monitor (CRM) samples the air every hour for ~48 hours to provide an average radon level for a house. If the windows and doors are left open during a portion of the radon test, this could seriously impact the report because the testing window is so small that the high radon levels caused by the pressure differential of open doors/windows would greatly report the reported levels. These fluctuations would not have as much an impact on the readings if the test occurred over a 90 day period.
*This example is important because a radon inspection during the real estate inspection period is meant to help inform the potential buyer of the property if radon is or is not an issue they need to be concerned with if they were to live in that home.
How do Radon Professionals account for these variables? A common practice in the Radon space is something called “Closed Home Conditions”. This effectively means that 12 hour before a short-term test begins all exterior doors and windows need to be closed. This will allow air pressure between the inside of the home and outside to normalize. These exterior doors and window must remained closed (except for normal entry/exit) during the testing period to allow for more accurate results. Your radon professional should be advising the occupants of the residence to abide by Closed Home Conditions at least 12 hours before the test and should conduct a visual inspection upon arrival at the site to confirm that these conditions have been met.
Hopefully this helps you understand more about what can affect the accuracy of your radon test. Do not hesitate to contact a Lung Radon professional if you have any questions.