The cost of the actual radon test itself is not expensive. Some home inspectors will provide a Canister kit to test the radon for which they charge their clients $100′ish (give or take), while others bring a machine for which they charge $125′ish (give or take). The canisters have to be sent to a lab to be processed, and so it can take up to a week from when the canisters are placed until you receive the results. The machine, on the other hand, provides its results two days after the administration of the test or as soon as the machine is picked up. When my buyers ask if they should test for radon during the home inspection, in almost every case, I say yes. And I answer this way even if no one is going to be using or spending any time in the finished room in the basement…. Even if a test was done six months before and the result was 2.0 pCi/L, for example. According to the RSSI, “Radon levels vary in daily and seasonal cycles and in response to weather conditions and ventilation patterns,” and so a six-month window might present too many variations to the testing conditions…. And even if the home currently has a radon mitigation system, which “seems” to be working properly. The only time that I might advise not to conduct a radon test is if a previous test was done within the last 30 days, there weren’t any structural changes to the home or its ventilating, heating and/or cooling systems during that 30-day time period, and the test result was 2.0 pCi/L or below. In this case, given the 2.0 pCi/L level of the prior test results and the fact that the conditions are fairly consistent with those of the previous test given the short 30-day window combined with my client’s desire to waive administering the test, I would concur. But only after we had reviewed, verified and were comfortable with the prior test results.