When do you need multiple radon systems

Pressure Field Extension

Avid blog readers will know this term.  Pressure field extension, or PFE for short, is an industry term for the area under the home where the radon fan has influence.  If you can remove 100% of the air beneath a home, then you’ve solved your radon problem*: we call this “perfect” pressure field extension.

Radon systems are soil depressurization systems.  Homes that aren’t designed with radon in mind actively pull soil air.  A radon system short-circuits this stack effect and pulls air or depressurizes the soil.  How far across a foundation or how deep into the soil you pull from is your “pressure field”.

*99% of homes the radon source is the soil.  Read about the other 1% here.

Measuring PFE

To measure PFE, you need to build out a radon system OR you need to mimic the effects of a radon system.  This is why PFE testing and proper fan sizing are not industry standard practice.  Most radon systems are needed “under-the-gun”.  There is a home sale** deadline approaching and many of the decision-makers are most concerned with time and immediate cost and less concerned with system efficiency and lifetime energy cost.  “Poke and hope” is what most mitigators do.  They “shoot from the hip”, so to speak.  Depending on their training and experience this can be an acceptable risk to take OR it can be disastrous and unethical.  This is why it’s so important to start with a certified professional.  These contractors have at least shown the aptitude to pass the exam and understand the material.  Whether or not they practice their skills in real-life is something you may be able to discern from their website photos and google reviews.

Measuring PFE involves creating a temporary radon extraction point.  For slab systems*** this may mean digging out some sort of suction pit.  It may not be the final version of what you have, but it will allow you to hook up a PFEDK or a shop-vac-version to mimic a radon fan air flow.  From there, the skilled tradesman will dig pilot holes (often 1/8″ or thereabouts) all over the foundation to see if they can effect the pressure field from this tentative extraction point.  Can they pull air (see negative pressure)?  These diagnostics tell them what they need to know about soil conditions, moisture, intermediate footers, and baseline pressure dynamics of the home.  This service takes time, skill, and money and is not standard in most radon mitigation transactions.  Often times it’s done after the fact when the original poke-and-hope system has failed.

Watch PFEDK tutorial videos here to see how involved this process can be

**Read our radon considerations for home buyers here 

***crawlspace foundations it is assumed that you can get 100% PFE on sight with proper design considerations.  As long as there are no full walls or separations between them.

Foundation types

If your home is 100% crawlspace, then you theoretically have the simplest extraction point system (other than a properly designed RRNC home).  A perforated pipe or geotextile mat loop will gather all the air you need, then you can size your fan and build out a single system.

What if your home has multiple crawlspaces?  Walls separating them?  What if it’s got a garage slab, a foundation slab, then an addition that is a crawlspace?  This is typically where multiple radon systems are necessary.

Imagine: is there anything that would inhibit my pressure field from a single extraction point?  

Common examples and considerations include:

• Multiple foundation types (slab, basement, garage, and/or crawl).
  • Especially those that are difficult to tie together with PVC above the sub-floor
  • Radon fan placement is a big consideration.  Perhaps you can tie multiple systems together, but have to place the fan near a master bedroom to do so.   Would it be better to have two smaller fans in lesser used areas of the home?
• Intermediate footers on a slab.  Footers that run the full length or width of a foundation will cut PFE.
• Homes with additions
• Improperly designed passive systems that need to be torn out or supplemented with a post-construction system
• Sump systems with failed pumps or a lack of dry drain-tile to utilize for PFE.  Radon systems cannot pull through water.  Water always short-circuits them

Conclusion

These are just a few of the considerations that a certified, ethical radon contractor must deal with every day.  The sum of their career experience is invaluable.  They know your city, your neighborhoods, and your building styles better than many general contractors.  When you’re paying for a radon system, your not just paying for pipe and fans, you’re paying for the career hiccups and knowledge-gained so that when difficulties inevitably arise, you’re taken care of.  Read more about system cost and deciding factors here.

Thank you for reading!