Activating a Passive Radon Mitigation System - American Radon Mitigation

Activating a Passive Radon Mitigation System

In June 2009, the state of Minnesota began to require that new construction homes include a passive radon mitigation system. What is a passive radon mitigation system? In short, it provides the framework for an active radon mitigation system, so if a home tests high for radon in the future, the problem can be more easily addressed. Theoretically, to activate a passive radon mitigation system, a mitigator should just need to add a fan and gauge. However, in our experience, activating a passive system is a bit more involved. We aim to create a quality system that lowers radon levels as much as possible, and passive radon mitigation systems generally need some extra work to achieve that. In this post, we’ll take you through the process of activating a passive radon mitigation system in a Minnesota home built in 2015 with a radon level of 2.9 pCi/L. This seemingly simple activation became a bit of a challenge, demonstrating that installing a fan isn’t always enough on a passive radon system. 


Before we get started, we need to know what radon is and why mitigation is so important. Radon is a radioactive gas that is released from the breakdown of uranium in rocks and soil. This toxic gas can raise from the ground and collect in your home. Radon is the leading cause of lung cancer among nonsmokers in the US. You can learn about radon testing here. The EPA recommends mitigating levels at or above 4.0 pCi/L; however, there is no safe amount of radon exposure. Our goal is to lower radon levels in your home as much as possible to keep you and your family safe. 


A passive radon mitigation system consists of a gas-permeable layer, usually four inches of clean rock underneath the concrete floor in the basement and it has a six-millimeter vapor barrier. There’s also a three-inch pipe that runs to the gas-permeable layer all the way up through an interior wall of the house, into the attic, and out through the roof.  There should be electrical next to the pipe in the attic if a radon fan needs to be installed. State code in MN at this time requires an outlet within six feet of a radon fan. 


Our first step in this project was installing the radon fan. We cut out a section of the three-inch pipe that ran from the roof down to the sub-slab material. There was already an outlet within six feet of the fan, so we didn’t have to worry about additional electrical work. (We always work with a licensed electrician.) 

Installing Radon Fan on a passive radon system

We also wanted to make sure that the pipe was pitched to allow for proper condensation drainage. The pipe was fairly level, so we adjusted it accordingly.

Ensure radon system pipe pitch allows for condensation drainage


At this point, we technically had an active radon mitigation system. Some mitigators would add a gauge and stop there. However, adding a fan doesn’t ensure that the system is working effectively or efficiently. To achieve optimal performance, we always take additional steps when activating passive systems.

We’ve found that the key to getting radon levels as low as possible is to create suction under the entire house. To measure the suction, we always conduct pressure field extension testing. To test, we drilled half-inch holes in far areas of the home where suction was likely to be the weakest. Then, we plugged a tube into each test hole and ran the tubes back to micromanometers, showing us how many pascals of pressure we achieved. Ideally, we’d like -5 Pa in the farthest, weakest test hole in a home.

Pressure Field Extension testing to measure pressure under the home


We also sealed any gaps or cracks that were open to the soil. Sealing gaps ensures that we are creating strong suction under the home and helps the system run more efficiently. These openings can also suck conditioned air out of the home, which ends up costing the homeowner more money in the long run so we want to make sure they are sealed. 

The sump pump had a huge opening to the soil, so we installed a clear Lexan cover with and access port to seal that off. 

Sealing sump pump cover to lower radon and increase energy efficiency of the radon system

Next, we moved on to large gaps and cracks. You can typically find these near the floor-to-wall joint. As the concrete floor cures, it shrinks and creates a gap where it meets the wall. There also tend to be openings under bathtubs or showers. 

We cleaned the cracks out with a wire brush followed by a shop vac. To seal them, we used a low-VOC radon sealant (As an Amazon Associate, we earn from qualifying purchases). Then, we simply ejected the radon sealant into the cracks and smoothed it out with a finger.

Sealing cracks in the floor with low-VOC radon sealant to increase radon system efficiency

In this house, we had a large gap under the sheetrock and trim on the other side of the wall from our suction point. To reach, we had to pull the carpet back. We cleaned that gap out with our brush and shop vac, and then we used a small-tipped foam gun to inject foam into the gap (As an Amazon Associate, we earn from qualifying purchases). After everything was sealed, we put the carpet back in place.

Sealing gap under sheetrock to increase radon system efficiency


Once we had completed our sealing, it was time to go back and check our pressure field extension. We found that our test holes were reading about -0.4 Pa, -1 Pa, -0.3 Pa, and -4.6 Pa. Remember, we wanted at least -5 Pa, so we still needed to make some adjustments to the system. 

Pressure Field Extension Testing of the radon system


To investigate, we took our pipe apart and put a cable camera inside to see what was happening. We discovered that a three-inch T below the slab, as pictured below, was filled with rock, preventing proper airflow. This T should have been connected directly to the drain tile or at least ten feet of perforated pipe to prevent airflow resistance. 

Three inch T connects directly to the drain tile and should be free of rock and debris

To increase airflow, we drilled two five-inch holes through the floor, one on either side of the T, and dug out about ten gallons of rock. 

Increase air flow of the radon system by ensuring drain tile is not blocked

Once we were done, we plugged the holes with styrofoam, sealed them with foam, drilled Tapcon screws in, and poured concrete over the top.

Plug cored holes with Styrofoam, Tapcon screw  and concrete

Despite our best efforts, our suction still wasn’t as strong as we wanted. So ultimately, we added an additional suction point.


Next, we installed a U-Tube manometer, a gauge that indicates whether or not your system is working. There is a small tube that inserts into the system’s pipe. If the system is working properly, it will create suction and draw the blue fluid up so that the levels are uneven, as shown below. 

If radon system is working properly it will create suction and draw the blue fluid up

If the blue liquid is level at zero, your system is not creating suction.

If liquid is level at zero, radon system is not working

We also added an alarm, which would audibly alert the customer if the system stopped working.

Radon alarm audibly notify when radon system is not working


Even after sealing and adding a suction point, we still were not quite getting the suction we wanted under the house. So we decided to try a larger fan. Initially, we installed a Fantech Rn2EC. Generally, the Rn2EC is more than powerful enough to activate a passive system, but this project had some unusual challenges. We didn’t start with the largest fan because it would have a higher operating cost. The key is getting the right fan to balance efficiency with effectiveness.

We decided to switch to the Fantech Rn4, which had more power than we needed.

Fantec RN4 radon system fan

Both the Rn2EC and the Rn4 have a dial that allows us to adjust the fan’s settings specifically for our system. We adjusted the fan until we hit -5 Pa in our weakest test hole.


Once we achieved our desired suction under the house, it was time to wrap up. We plugged our diagnostic test holes and restretched the carpet so that no one would know that we had been there.

Plug test holes, re-stretch carpet and leave home better than you found it

The final step in any mitigation is a radon test to ensure that the system is effectively lowering radon levels. We provide customers with Air Chek test kits as they’re EPA-approved, quick, and easy to set up. For example, this customer’s radon levels began at 2.9 pCi/L. Our final test results came back at 0.4 pCi/L.

Radon Test KIts

If you’re looking to get your radon levels as low as possible, contact us to learn more about radon testing or get a free estimate for radon mitigation.

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