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Testing for Radon: The Do’s and Don’ts<

Real estate professionals play a key role in New Jersey’s efforts to reduce radon exposure among residents. Since 1986, when radon was first discovered to be a health hazard in homes, radon testing has been integrated within most real estate transactions in New Jersey. In fact, 75-80% of the approximately 60,000 radon tests now done in New Jersey each year are done as part of real estate sales, according to the database of testing information maintained by the New Jersey Department of Environmental Protection (NJDEP) Radon Program. Although most real estate professionals are well informed about radon, questions occasionally arise about the proper conduct of tests. Following are the essential do’s and don’ts.


  1. Know about radon in general, so that information you provide to clients is accurate. Most important, be aware that only state-certified companies can test for and mitigate radon. The only relevant exemption to this legal requirement is where homeowners perform tests or mitigations of their own homes.
  2. Refer clients to experts rather than attempt to answer questions when you’re unsure of the answers. Clients can be referred to the NJDEP Radon Program (1-800-648-0394, or, or to certified radon companies.
  3. Be aware of a seller’s obligation to reveal to a prospective buyer the results of all radon testing and any mitigation. Under the law, the seller must provide the buyer, at the time the contract of sale is entered into, with a copy of the results of the radon test and evidence of any mitigation or treatment.


  1. Don’t become involved in any aspect of the testing process. Even sealing and mailing back the test kit would interfere with the process. The certified tester will inspect the test site when they pick up the test to ensure that there has been no tampering, that proper testing conditions were observed, and that the environment of the home has not changed (such as water in the basement following a rainstorm.) For either the real estate professionals or the homeowner to send back the test kit would render the test invalid (with the exception that homeowners can legally perform this task if they are paying for the test).
  2. Don’t suggest that clients could open windows to vent radon. Radon tests require "closed house" conditions, meaning that all windows and doors that could let outside air enter the home should be kept closed during the test, except for normal exit and entry. If the test is less than four days in length, closed house conditions should be maintained an additional 12 hours prior to the start of the test. If closed house conditions are not maintained – and it is possible that the tester or home buyer will drive by to check -- the test will be invalid, and the real estate professionals could be legally liable for their advice. (In addition, it is a little-known fact that opening windows in some cases actually increases radon levels, rather than decreases them.)

Radon is the most serious environmental health risk faced by the average person. The latest national review of radon risk data, sponsored by the National Academy of Sciences, not only supported earlier assessments of risk, but actually raised risk estimates. The study examined lung cancer and radon exposure among 68,000 miners of whom 2,700 have died from lung cancer. It reviewed laboratory evidence on the impact of radon on individual cells and on laboratory animals.

The review, published in 1998, concluded that between 15,000 and 22,000 Americans die each year as a result of lung cancer caused by radon. To put this risk in perspective, 45,000 deaths occur in the U.S. due to motor vehicle accidents, 4,000 deaths due to fires and 4,000 deaths due to drowning in a typical year, according to the National Center for Health Statistics.

The risk of radon for smokers is much greater than for nonsmokers. For a nonsmoker who has an average radon exposure of 4.0 pCi/L over their entire lifetime, the risk is 1 in 500 of developing lung cancer due to radon. The risk for a smoker in the same situation is 1 in 35 (in addition to the risk of lung cancer from the smoking itself). Radon Risk Comparison for Smokers and Nonsmokers (Source: USEPA Physicians Guide, 1993)

Radon Level (in pCi/L) Odds for smokers of developing lung cancer if exposed to this level over a lifetime.* Odds for nonsmokers of developing lung cancer if exposed to this level over a lifetime.
20 1 in 7 1 in 125
8 1 in 18 1 in 333
4 1 in 35 1 in 500
2 1 in 67 1 in 1000
0.04** 1 in 333 1 in several thousand

*This is in addition to the risk of lung cancer from smoking itself.
**Average outdoors radon concentration.

A common misconception about radon is that it is only a concern in a few areas of New Jersey. While radon concentrations do vary from region to region, there are high- and moderate- radon areas scattered throughout most of the state. Even in low-radon communities there may be homes with significantly elevated radon levels. For example, homes in one municipality in Ocean County have tested as high as 23.7 pCi/L, even though the average test result for that community is very low at 0.98 pCi/L.

In addition, within each municipality, radon levels vary greatly from home to home. Indoor radon concentrations depend on highly variable factors:

  1. the distribution of uranium-rich rocks and soils near the home, and the porousness of the soil;
  2. the number and size of entryways into the home, such as tiny cracks in the slab, French drains, and sump pits; and
  3. the air pressure in the lowest level of the home, which is affected by heating, cooling, and exhaust systems, as well as by the weather (the lower the air pressure in the home, compared to outside air pressure, the more quickly radon will enter the home).

As a result, it is not uncommon to have a home with very high levels next to a home with extremely low levels. For these reasons, the NJDEP recommends that all homes, thought the state, be tested for radon as a precaution.

The good news is that concentrations can be brought down to relatively low levels, through the installation of radon removal systems. According to test data collected since 1991 by the NJDEP Radon Program, radon levels have been reduced to less than 1.0 pCi/L in about half the homes in which radon remediation systems were installed -- even when the pre-remediation levels were very high. Although even low levels of radon still have risk associated – and even in the outdoors environment there is a low level of radon, averaging 0.4 pCi/L -–most remediations succeed in reducing indoor radon levels very significantly so that cumulative exposure for residents is sharply reduced.

Approximately 2400 homes are being remediated each year in New Jersey, according to the NJDEP. Since remediations typically result in more than a 90% drop in radon exposure for the residents of the home, this represents a dramatic risk reduction for about 20,000 New Jersey families during the past decade.

The NJDEP Radon Program appreciates the efforts of real estate professionals to ensure that radon testing is done properly during home sales. If real estate groups are interested in learning more, the Program can provide a speaker with a slideshow presentation, or a ten-minute videotape about radon testing. To arrange a speaker, order the videotape or other materials, or obtain other specific information about radon, contact the NJDEP Radon Program Helpline, 1-800-648-0394, or the Program’s website,

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Last Updated: January 4, 2019