Passive vs. Active Mitigation Systems

We have received a really great question from a few buyers recently: If a mitigation system is already installed, should I still test for radon gas?

Here is our recommendation on how to approach radon testing once you have been notified that a mitigation system is already installed.

First, ask if the radon mitigation system is passive or active.

An active system has four elements:Radon-Diva-Radon-Mitigation-System

  • an electric vent fan (1)
  • a system failure warning device (may also be in the basement) (2)
  • a vent pipe running between sub-slab gravel up to above the roof or eave (3)
  • sealed and caulked cracks and joints. (4)

Keep in mind, the estimated life of a quality vent fan (operating continuously) is 5 years or more. Manufacturer warranties tend to expire after 5 years.

There are several methods a contractor can use to lower radon levels in your home. To learn more about the different types of radon mitigation systems, click here for the Environmental Protection Agency’s “Consumer’s Guide to Radon Reduction: How to fix your home.”

A passive system is typically installed at the time the house was constructed and has two elements:

  • a vent pipe extending from the sub-slab gravel up to above the roof or eave (3)
  • a physical barrier (polyethylene membrane) between the soil and house foundation. (5)

Source: ASHI (American Society of Home Inspectors) Radon Mitigation System Inspection Checklist found on the Environmental Protection Agency’s website.

In summary, the main difference between passive and active radon mitigation systems is that the passive system relies on natural pressure differentials and air currents instead of a fan (used with active radon mitigation systems) to draw radon up from below the home.

Now that you know if the system is passive or active, what’s next?

If the radon mitigation system is passive

Per the Environmental Protection Agency, “Passive subslab suction is generally not as effective in reducing high radon levels as active subslab suction.” These systems will reduce radon levels but may not reduce the levels below the 4.0 pCi/L action level. Because of this, we recommend testing the home for radon gas. If the test result is 4.0 pCi/L or above, a qualified radon mitigation contractor can easily add a vent fan to an existing passive system to further reduce the radon level in the home.

If the radon mitigation system is active

It’s always a good idea to independently test the home for radon by using a licensed radon professional.

You can also ask the sellers for a copy of the test results from a radon test performed after the mitigation system was installed. Be sure to verify that the mitigation contractor who installed the system is licensed by the state of Ohio by clicking here.

If test results cannot be supplied or they are from more than 2 years ago, retest. The Environmental Protection Agency recommends retesting the home every two years to ensure radon levels remain low.

Radon Diva is always here to answer any questions you may have. Give us a call today!


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