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When we get this call by phone, most DIYers think that they need “higher” pressure. They say their radon system “doesn’t have enough vacuum”. I’m not sure where this need for vacuum came from, but in my experience, the opposite is true. You need airflow. If you’ve read my articles on fan sizing and fan curves, you know that vacuum and airflow have an inverse relationship. So the higher your vacuum, the lower your airflow.
That’s not to say higher vacuum is always bad. Sometimes you need a high suction fan to extend your pressure field (PFE) across the entire home.
As always, the best solution is to have a licensed radon mitigator perform proper fan sizing and PFE testing. Make sure you ask for this service on your inquiry call, as it’s not a standard service all NRPP pros provide. It may cost a little more, but in the long run, the energy savings will often outweigh the upfront costs.
So, Brent, what is a good vacuum pressure for my radon system?
Well, more than zero. That’s all I can say with certainty. More than zero and less than the functional maximum listed by the fan manufacturer (see fan curves).
What happens if I have no pressure?
No pressure could mean a few things: your fan is off or has no power; your system has a substantial leak (loose pipe, ripped barrier, etc.); or lastly your manometer is malfunctioning or disconnected. These are typically easy fixes that any system inspection will reveal quickly.
What if I have pressure, but my radon levels are still high?
This is very common. This means that you don’t have PFE, so your system is not covering the entire living space. On suction pit systems, usually you need a bigger pit (see here) or larger pipe (4” rec.). On crawl space systems, it needs to have a perf pipe or gas mat loop below the barrier to get PFE. Is everything sealed? Are there pony walls or multiple crawls? Are these connected? Lastly, and least common, is your fan just too small? Did the contractor put on a cheap imitation fan or a low volume fan to save money? Was any fan sizing or PFE testing performed or did they “poke and hope”?
If this article hasn’t given you a direction to work with, then it’s time to call an NRPP licensed pro. Remember, most states have no licensing or training requirements, so just by making it down to this sentence, you may have more knowledge than the radon “pro” you found online. Be safe; ask for credentials; and test for radon every five years no matter what!
