Not All Radon Tests Are The Same: Continuous Radon Monitors vs Charcoal Canisters

Not All Radon Tests Are The Same:

Continuous Radon Monitors vs Charcoal Canisters 

BY Bruce adams

1st Priority Home Inspections, LLC TN Lic#1274


The EPA radon risk map shows middle Tennessee as a high radon risk area. Testing for radon can be conducted using several different types of radon monitoring equipment approved for real estate transactions. The two most common are charcoal canisters and continuous monitoring equipment. Many home inspectors use the charcoal canisters for radon testing because they are inexpensive compared to $1000-$5000 for professional continuous monitoring equipment. We use EPA verified, NEHA-NRPP listed and evaluated NRSB approved professional equipment for several reasons.

1.       Charcoal canisters do not provide immediate results. The charcoal canisters must be mailed to a laboratory to be analyzed before getting the final results. This process can take from three to five days. Waiting for the results of a radon test for this long can sometimes put the home inspection contingency over the time limit and generally leaves no room for a follow up test if levels come back elevated.

2.       Another reason to use continuous monitor systems over canisters is rain. Rain infiltrating voids and cracks in the ground can drive radon out and result in elevated readings. With the continuous monitoring system fluctuations of radon levels throughout the test can be observed and a knowledgeable inspector can determine if an elevation of levels may be the result of rainfall. Knowing this, a decision can be made to retest the property or to recalculate the average after removing the artificially high readings from the rainfall event. Charcoal canisters do not provide any of the information needed to make this type of decision or recalculation.

3.       In presale radon testing tampering is a major concern. To skew the results, a home owner can simple take the radon monitor out of the home and place it outside where radon levels will be lower, then put it back in the home prior to the inspectors retrieving the device. The continuous monitoring device that we use has anti-tampering features that will indicate if/when the monitor was moved. Tampering cannot be detected with charcoal canister systems making any results potentially suspect.

******* 4/21/2016 *******

Time Counts Flags


14:49 1.1

15:49 1.5

16:49 1.8

17:49 1.1

18:49 1.2

19:49 1.5

20:49 1.5

21:49 1.8

22:49 1.5

23:49 1.5


******* 4/22/2016 *******

Time Counts Flags


00:49 2.3

01:49 1.6

02:49 2.6

03:49 1.5

04:49 5.6

05:49 6.5

06:49 7.5

07:49 6.9

08:49 6.7

09:49 6.5

10:49 6.9

11:49 6.7

12:49 6.2

13:49 5.8

14:49 5.5

15:49 2.2

16:49 1.5

17:49 0.7

18:49 2.5

19:49 2.6

20:49 1.9

21:49 1.9

22:49 1.5

23:49 1.8


******* 4/23/2016 *******

Time Counts Flags


00:49 1.5

01:49 1.4

02:49 2.5

03:49 2.0

04:49 2.7

05:49 2.9

06:49 2.5

07:49 3.6

08:49 4.2

09:49 3.3

10:49 3.2

11:49 4.7

12:49 2.2

13:49 1.8




Overall Avg: 2.9 pCi/l

EPA Avg: 3.0 pCi/l

Above is a good example of how rain can adversely affect a radon test. During the timeframe of the readings highlighted in red, a cold front and rain moved into the area of the home being tested resulting in the radon levels rising. In this particular case the home still ended up being below the 4 pCi/l limit the EPA recommends remediation at but was still in the 2-4 pCi/l that the EPA recommends considering remediation. Because a monitoring device was used, we were able to make a reasonable assumption that under normal conditions the home is below 2 pCi/l so no further action would be recommended. If this had been a canister test we would only have received the average pCi/l and had no way to correlate the elevated results with the rain.


For further information on Radon visit our website at or call 1st Priority Home Inspections, LLC at 931-260-7829 to schedule your radon test.