Contunuous Radon Monitors v/s Charcoal Canisters

Home Inspector with Complete Home Inspections, Inc. TN Lic#050

The middle Tennessee area is considered a high radon belt according to the EPA. There are several different types of radon monitoring equipment in the marketplace approved for real estate transactions. The most common are the charcoal canisters and the continuous monitoring equipment. Some home inspectors like to use the charcoal canisters for doing their radon testing. These are inexpensive costing about $10 each as compared to $1500-$4000 for a good grade of continuous monitoring equipment. I prefer to use the continuous monitoring equipment and here’s why:

  1. One cannot get instantaneous readings from the charcoal canisters. The charcoal canisters must be sent off to a laboratory to get the final results and generally, this can take from three to five days. In this fast paced real estate market waiting for the results of a radon test and sometimes but the home inspection contingency over the time limit.
  2. Another reason that I prefer to use the continuous monitor system is rain. Rain can drive radon out of the ground and depending upon the location of the property and how many inches of rain has been delivered by the storm, radon levels can get skewed. With a visual representation of elevated readings, a competent home inspector can determine if the rainfall has adversely affected the radon test. At that point the decision can be made to either retest the property or back the elevated readings out and recalculate the average for the property. You cannot do that with charcoal canisters.
  3. Another reason that I prefer the continuous monitor system is tampering. Sometimes the homeowner will take the radon monitor out of the house place it on the back porch and then put it back in the House today that the inspectors to return and retrieve the device. The devices that I use have anti-tampering that record time and temperature as well. If I notice any sudden temperature changes in the output of strongly suspect tampering and note that in my report. Once again, tempering cannot be detected with the charcoal canister system.

A good example of how rain will adversely affect a radon test will start with the red arrow and end with the blue arrow. During this time period, a cold front and rain had moved into the area causing the radon levels to rise in the property. This is quite normal to see. I have seen some storms drive the radon levels up past 100 pico-Curies per liter. However in this test the radon levels remained relatively low and really did not adversely affect the total outcome for this particular property.

I hope that this information is been helpful to the real estate community and shed little light on radon monitoring systems.

This posting and the contents written here are the intellectual property of Michael Thornton of Complete Home Inspections, Inc. providing home inspections for Brentwood, Nashville, Davidson and Williamson Counties of Middle Tennessee. The views and opinions expressed are just that - views and opinions of Michael Thornton and those who comment. This post is a contribution to the ActiveRain Real Estate Network.

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Complete Home Inspections, Brentwood TN 615.661.0297


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Charles McDonald
Charlottesville Real Estate Solutions - Charlottesville, VA
REALTOR®, Blogger, Principal Broker®, Owner

Excellent point, I am having 2 inspections done this week with radon testing too... We never use charcoal.

Your Friend in Charlottesville Virginia!

Apr 14, 2008 12:11 AM #1
Larry Brewer - Benchmark Realty llc
Benchmark Realty LLc - Nashville, TN
Michael - Not wanting to sound like an ignorant realtor, but what would be a safe reading and a bad one. I doubt if many of us know what we are looking at here.
Apr 14, 2008 12:12 AM #2
TeamCHI - Complete Home Inspections, Inc.
Complete Home Inspections, Inc. - Brentwood, TN
Home Inspectons - Nashville, TN area - 615.661.029
Larry, Anything above 4.0 pCi/l is considered high.
Apr 14, 2008 12:18 AM #3
Sean Allen
International Financing Solutions - Fort Myers, FL
International Financing Solutions

Hey Michael,

That is some interesting stuff about Radon gas. I don't recall hearing much about this when I was in Kentucky.

Sean Allen

Apr 14, 2008 02:35 AM #4
Rob Kleinschmidt
Pillar To Post Professional Home Inspections - Lake Geneva, WI
Continuous monitors are definitely an advantage.  Faster turnaround times on results, hourly readings and printouts on most, and anti-tamper devices are only a few advantages.  We always use continuous monitors.
Apr 14, 2008 04:08 PM #5
Harold "Hal" Place
A1 Connection Realty, Inc. - Sun City Center, FL

Morning Michael,

Thanks for another informative post. We have very little experience with radon testing here. Thanks to your post I will be better informed when a buyer inquires as to the best testing method.

Have a great day!


Apr 14, 2008 09:59 PM #6
Susie Blackmon
Ocala, FL
Ocala, Horses, Western Wear, Horse Farms, Marketing

This is a great post Michael, especially for those of us who deal with radon issues!  The continuous monitors, in my humble opinion, are what I want - - FAIR!

Apr 14, 2008 10:18 PM #7
James Quarello
JRV Home Inspection Services, LLC - Wallingford, CT
Connecticut Home Inspector


I always use continuous monitors for radon testing. In my opinion it should be the only method for a real estate transaction.

I would however somewhat disagree with your explanation of rain and radon.

Rain does not drive radon from the ground, it creates a barrier thus forcing the gas to take the path of least resistance. Other weather related events can also affect radon levels such as high winds, barometric pressure changes and cold weather. The time of year and even the time of day have been documented to cause fluctuations in levels.

I would not invalidate a test because it rained during the test period. This is a representation of what would occur under normal conditions in the home. If levels elevate 100 pCi/L during a rain storm that is relevant information. If it occurs then it will occur during all types of weather events as I described.

This is where using monitors sometimes can be "too much" information. In CT where I work testers who use monitors are required to be NRSB or NEHA certified. The reasoning is you must be able to interpret the readings where other devices do not require such interpretation.

Apr 15, 2008 01:15 AM #8
Paul Gapski
Berkshire Hathaway / Prudential Ca Realty - El Cajon, CA
619-504-8999,#1 Resource SD Relo

thank you very much for the informative and interesting post. I get so much out of the active rain network.

Mar 13, 2012 01:38 AM #9
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