Using Pressure Field Extension To Track Down Radon Entry Points - American Radon Mitigation

Using Pressure Field Extension To Track Down Radon Entry Points

Using Pressure Field Extension (PFE) To Track Down Radon Entry Points

In this article, we will discuss how we used pressure field extension testing to track down hard-to-find radon entry points. We initially installed this radon system in September, and we had weak pressure field extension in some of our test holes, but the radon levels were low. We talked to the homeowner and presented their options. In this case, they chose to wait on further mitigation steps to see how the radon test results came back. 

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Initial Radon Results

Six months later, they completed two radon tests. The basement test came back at 3.8 pCi/L, and the room above the garage came back at 2.8 pCi/L.

Home with Tuck Under Garage

For this home, we originally added one suction point. When we returned, we added two additional suction points. We came back the next day to find the radon levels had not dropped as much as we had hoped. In our experience, homes with a tuck-under garage, like this one, can require pressure field extension into the garage to lower the radon levels. Let’s find out if we needed to mitigate the garage and what steps we took to locate the radon entry points.

Original Suction Point and Fan

The original suction pit was an 18-gallon pit of fine sand. It was next to plumbing, which gave us the best results for pressure field extension. The radon pipe went from the pit up towards the center of the house, through a chase, and to the radon fan in the attic. We used a Rn2 radon fan running 1.7 inches and moving 12 CFM.

Pressure Field Extension

In this home, we had pressure field extension in all of our test holes except two.

The first was the test hole in the front right corner of the garage, which was positive.

The second was in the bathroom, which was also positive. In the bathroom was a sump with no drain tile, just a sump basket with holes drilled into it to allow water to weep in. 


When we returned to this home, we figured it would be simple: We would just need to make the front right garage test hole and the sump test hole in the bathroom negative. But it was not that simple.

Second Suction Point

Sump Radon Suction Point

We started by adding a second suction point on the sump and created a small pit there. The suction pit was about 3 gallons.

Third Suction Point

Radon Suction Point

We added a third suction point under the entryway. This suction point had 13 gallons of fine sand. It also had block on both sides of the pit where you would normally expect to find footings. The footings were very deep here because the front step was so close to grade.

Tying It All Together

PVC T to tie radon suction points together

We connected suction points 2 and 3 to the original radon system in the mechanical room using a T.


Sealing bed joints

When we originally mitigated this home, the mechanical room had sheetrock covering most of the foundation walls. When we returned, we found out the homeowner had identified foundation issues that had to be corrected. Since the sheetrock was removed we were able to access and seal the bed joints that had opened.

We also found the tops of the blocks were open, and when suction was applied to the radon system, the top of the block leaked, so we sealed that as well.

Day 2 Results

After adding the two additional suction points and sealing, we thought we would come back the next day to lower radon levels and be able to clean up and be done. However, the EcoTrackers we set up overnight showed the radon was not as low as we hoped the next morning. They were actually higher than we thought.

The EcoTrackers measured 5.1 pCi/L under the front step by suction point 3. The bathroom and front corner of the house were 2.8 and 3.0 pCi/L. The garage was 1.5 pCi/L.

Fourth Suction Point

Since the area under the entryway was still the highest at 5.1 pCi/L we decided to add a suction point to mitigate the front step. When we drilled that suction point, we placed the EcoTracker in the hole under the front step, and it quickly rose to 12 pCi/L.

Mitigating The Front Step

To treat under the front step, we first used a template to trace an area on the foam board insulation. Next, we used a Sawzall to cut and remove the foam board.

Once we had access to the block behind, we measured to ensure that the 5” hole landed on the core rather than going through the block’s web.

Drilling radon suction point in block wall

Next, we drilled a small hole that would receive the pilot bit for the 5” core drill.

Now that we had the hole cored, we excavated the suction point.

Smoke Test on Radon Suction Point

We placed an EcoTracker inside the pit to see what the radon levels were under the front step. We also puffed smoke using a TEC Fog Puffer into the front step, and the smoke came back towards us. This was a good indicator of what was happening to the radon trapped under the front step, which was being drawn into the house. This was likely why this area was tested at 5.1 pCi/L.

Now, it is time to run the pipe. We start by cutting a 13” piece of four-inch PVC pipe and gluing it to a two-to-four reducer. We wanted to be careful to seal that pipe in the wall so that it drew from the suction point rather than the block wall cavity. To seal, we used Great Stuff foam to seal inside the block and radon sealant to seal the outside.

Then, it was time to put the foam insulation back in place. We cut a 5” hole through it that allowed the pipe penetration to pass through once it was back in place. We used aluminum foil tape to tape it back in place.

EcoTracker for Radon Mitigation

While we worked on the piping, we kept the EcoTracker in front of the pipe opening. The radon levels were about 12 pCi/L, which shows that the front step was definitely contributing to the elevated radon in this home.

Finally, we glued everything together and tied it into the rest of the system. We used a valve to balance the system and control how much air we pulled from the front step area.


Once we applied suction to the front step, we noticed the radon levels started to drop to 2 pCi/L or less pretty quickly. The post-mitigation radon result for this home was 0.5 pCi/L.

If you are a mitigator or homeowner with a radon system that is not working as well as you would like, we offer consulting services. Learn more about our consulting services, and contact us to set up a virtual call.