Radon Testing Methods

Even if the house next door is radon-free, your property might have elevated levels of the gas. You may have heard that structures without basements don't have problems with radon, but that isn't true. The only way to know if radon is present in a structure is to test the air quality.

There are two basic types of radon testing devices, passive and active. Passive devices do not need power to function. These devices include charcoal canisters and similar units made from materials that absorb the gas. They are placed in the structure for a specific amount of time and then sent to a laboratory for analysis.

Active testing devices require power to function. They are meters that continuously measure and record radon in the air, making it easy to see when gas spikes and dips occur. Active devices are considered more reliable than passive testers, but since the equipment is expensive, they are used primarily by home inspectors and air-quality professionals and are not readily available to a homeowner.

Active devices sometimes have an anti-interference feature, which records when the device is moved. That can be an important factor when testing structures where you're not sure the seller will allow the device to remain in place during the testing period.

The most commonly used radon testing devices are passive units left in place for forty-eight to ninety-six hours. Long-term testing, done over a ninety-day period (or more), is usually more accurate, because time helps level out the spikes and dips in radon concentration. Investors and home-buyers don't usually have the luxury of taking ninety days to complete a test, so it's more common to see long-term tests used after a real-estate closing by an owner who wants to verify radon levels.

Tester Placement

The EPA recommends that you place the testing unit in the lowest level that can currently be used for living space. Choose a room that's used regularly but not a kitchen, bathroom, laundry room, or hallway.

Follow the EPA's recommendations for testing:

  • Close the room's windows and outside doors for at least twelve hours prior to beginning.

  • Keep windows and doors in the tested room shut, except for normal entry and exit.

  • Do not perform short-term tests during times of high humidity or high winds.

  • Place the testing unit at least twenty inches above the floor so that it is out of drafts. Do not disturb it during the testing period.

  • Follow the manufacturer's instructions to record the starting and ending times.

  • Reseal the package and return it to the lab for analysis.

Labs typically have test results ready in forty-eight hours or less.

Buyers usually want to do their own radon tests, but knowing the levels beforehand helps you price a property that might eventually require installation of a radon reduction system — something you will probably be asked to pay for.

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