Welcome to the State of California 

Radon Testing

Testing is the only way to find out if you have a radon problem. Homeowners can test their homes using inexpensive and easy to use test kits, or by hiring a Certified Tester to measure the radon concentration in their home. When testing for a real estate transaction, a Certified Tester should be used.


How Radon Is Measured

Radon levels are measured in picocuries ("pee-co-cure-ees") per liter of air, often noted as pCi/L. This measurement describes how much radioactivity from radon is in one liter of the air found in a home.

  • The EPA Action Level
    EPA and the U.S. Surgeon General strongly recommend that you fix your home if you have 4 pCi/L or more of radon in your home.

    There is no known safe level of exposure to radon since lung cancer can result from low exposures to radon. Exposure to radon at the EPA Action Level of 4 pCi/L poses a significant health risk. EPA based the 4 pCi/L Action Level on four factors: the health risk involved; the effectiveness of available mitigation technologies; cost-effectiveness; and, the goal set by Congress to reduce indoor radon levels to as close to the outdoor level as possible. EPA's estimate of radon-related lung cancer deaths is based on the population of the U.S. exposed to the national average indoor radon concentration of 1.3 pCi/L over a lifetime. Existing mitigation technologies allow the radon level in most homes to be reduced to 2 pCi/L or less most of the time.

    Additional EPA recommendation: To help minimize your future risk, you should also seriously consider taking action to fix your home if your radon level is between 2 pCi/L and 4 pCi/L.


How to Buy A Test Kit

Radon test kits can be purchased at most larger hardware stores, from a Certified Radon Service Provider, or online directly from a laboratory/manufacturer.

The Radon Program's partner laboratory is offering short term test kits for $7.95 to California residents. Contact Alpha Energy Laboratories (DrHomeAir) at 1-800-324-5928 to make your purchase. Test kits can also be purchased by clicking on the link below.  To prevent any problems with the processing of the order disable all pop-up blockers on your computer prior to entering data on the order form.


When Should You Retest Your Home?

Even if your test result is below 4 pCi/L, you should consider retesting your home every two to five years.

CDPH also recommends retesting for the following reasons:

  • Living patterns change: If you begin living in a lower level of your home, such as a new den in the basement, you should retest your home on that level.
  • If you finish or renovate an unfinished area, you should test your home before starting the project and after the project is finished.
  • Earthquakes, subsidence, and other natural ground shifts: A change in the ground beneath or around your home can open passageways in the soil allowing radon gas to enter your home.
  • Foundation shifts: As a home grows older, the foundation can shift; cracks and other openings can occur, allowing radon gas to enter the home.
  • After mitigation: If your home has been mitigated for radon, you should test again to make sure the radon mitigation system works. The system should be tested 24 hours after the system has been installed. You should also retest your home (in the winter heating months) every two years after a mitigation to make sure the system is functioning properly.


Types of Tests

Short-term test: The quickest way to test is with a short-term test. Short-term tests can be deployed between two days to 90 days, depending on the type of device. Charcoal canister, electret ion chamber, continuous monitor and charcoal liquid scintillation detectors are most commonly used for short-term testing.

  • If the average of the first and second short-term test is less than 4 pCi/L, no action is needed, but if you tested during the summer months, you might consider either a year-long test or another short-term test during the heating season.
  • If the average of the first and second short-term test is equal to or greater than 4 pCi/L, we recommend fixing or mitigating your home.

In California, the best time to use a short-term test kit is in the colder months, when radon levels typically tend to be naturally higher.

Long-term tests: Because radon levels tend to vary from day to day and season to season, a long-term test will give a year-round average radon level, whereas a short-term test can only tell you what your radon level is during the 2 to 4 day period that you tested. Long-term tests are deployed from 91 days to 12 months. Alpha track and electret detectors are commonly used for this type of testing.

  • Fix your home if your long-term test result is 4 pCi/L or more.
  • If you have never tested your home, start with a short-term test kit.  This will determine whether the home has a severe radon problem. If you receive results just under 4 pCi/L, you may want to follow up with a long-term test kit to confirm your home's average radon concentration.  


What do my Test Results Mean?

This charts shows the CDPH recommendations for your test results:

Test Type

Test Result 

Recommended Action if This is Your Home's First Test

Recommended Action if this is  a Retest

 Short Term

 less than 2 pCi/L

Retest every few years or when conditions change

Retest every few years or when conditions change


2-4 pCi/L

Consider retesting now, with a long or short-term test kit

 Consider fixing your home


 4-8 pCi/L

Retest Now with a long or short-term test kit

Fix the Home


greater than 8 pCi/L

Retest Now with a short-term test kit to confirm results

 Fix the Home

 Long Term

 less than 2 pCi/L

Retest every few years or when conditions change

Retest with a short-term test every few years or when conditions change


 2-4 pCi/L

Consider fixing the home

Consider fixing the home


greater than 4 pCi/L

Fix the home

Fix the home



Last modified on: 10/28/2015 10:13 AM