Colorado Now Regulates the Installation of Radon Measuring Devices

By now, most home sellers and buyers should be aware that radon, a naturally occurring carcinogenic gas, is prevalent in Colorado. Every buyer’s agent should be advising their client to hire an inspector who, in addition to inspecting the home for hidden defects, can perform a radon test.

Radon, at any level, can cause lung cancer, and the EPA has established an “action level” of 4 picocuries per liter (4 pCi/l) above which mitigation is recommended. According to, the EPA estimates that radon gas is responsible for 21,000 lung cancer deaths per year, about one-sixth of the annual lung cancer deaths ( However, if the radon level is above 4.0 pCi/l using any testing device other than a CRM (Continuous Radon Monitor), such as charcoal or E-perms, a second test is required immediately after, and those results are averaged with the first set of results to determine if mitigation is recommended.

Radon is an odorless, colorless and tasteless gas which is a decay product from Uranium U235. It further decays into polonium, which is what’s harmful to your health. The final decay product is lead.

Home inspectors are still not licensed or regulated in Colorado (something I have argued for), but as of July 1, 2022, only a licensed radon professional can install an approved radon testing device as part of a home inspection, and must follow explicit and detailed instructions for doing so.

Fortunately, my go-to home inspector, Jim Camp of Metropolitan Home Inspections, obtained his radon license and gave us a PowerPoint presentation on the subject at a recent office meeting. Here’s a link to his presentation.

Prior to licensing, any inspector could install the 48-hour testing equipment in a home and leave behind a flyer requesting “closed house conditions.” The device makes hourly measurements, so any violation of those rules would be obvious from looking at hourly variations in the measurements. Only the CRM has hourly results of the concentration levels along with temperature, barometric pressure and relative humidity reading.

But now there are several specific procedures that must be followed, including getting signed approval from the client to conduct the test, and providing advance notice of the test to the owner or occupant. The latter form states that closed house conditions must be initiated at least 12 hours prior to testing, not just throughout the 48-hour testing period.

Another rule is that if the basement footprint exceeds 2,000 square feet, two radon measuring devices must be installed. There are detailed instructions about where a testing device can and cannot be positioned.

Any air exchange systems, such as whole house fans, moisture mitigation systems for homes with structural wood or concrete floors, window air conditioners and box fans must be turned off. In addition, the garage overhead door must remain closed along with the windows and exterior doors including the passage door to an attached garage. An existing radon mitigation system can remain on during the test.

January Is National Radon Action Month. Here’s What You Need to Know:

Here in Colorado, about half our homes have elevated levels of radon, a naturally occurring gas created by the decay of radioactive radium in our soils. It is the leading cause of lung cancer in non-smokers. Here’s a link for an excellent YouTube video explaining radon and how it’s mitigated.

Most real estate professionals, including the agents at Golden Real Estate, are well aware of this issue and will always advise the buyers we represent to have the home they are buying tested for the level of radon gas as part of the home inspection process.

Notice that I didn’t say to test for the presence of radon gas, but rather the level of radon gas.  That’s because radon gas is present even in “fresh” air. But it can concentrate when it seeps into your basement, crawl space and even your above-grade living areas.

Since a high level of this gas is considered a “health and safety” issue, a seller is essentially obligated to accept responsibility for having the radon level mitigated or to compensate the buyer for doing it after closing. 

At Golden Real Estate, we have a hand-held device smaller than a TV remote which we can lend to sellers prior to listing their home so they’ll know in advance what level of radon a buyer’s inspector is likely to discover. Ace Hardware has this same device for sale for $199.

There are less expensive mail-in radon tests that you can purchase at Home Depot or Lowe’s, but they’re also free at multiple locations — including from our office at 17695 S. Golden Road in Golden. These DIY kits should not be considered adequate for use in a real estate transaction.

During the home sale, it’s best to have a certified radon measurement contactor do the official test. You can find a list at The test utilizes an electronic device which samples the air every hour over a 48-hour period. It can detect whether the device has been disturbed and whether there have been changes in atmospheric conditions which might suggest that windows or doors have been opened to allow fresh air into the house. Inspectors charge between $100 and $150 for this test, but it’s well worth the expense, especially if the results of the test show that the level of radon gas exceeds the EPA action level of of 4 picocuries per liter of air. If the test shows a level greater than that, the buyer can demand that the seller have radon mitigated. That typically costs about $1,000, so the testing is well worth the additional inspection cost.

Below is a diagram showing how radon is mitigated use sub-slab depressurization:

(from Wikipedia)