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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 pressure, 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.
For pressure discussions, I like to use the milk shake versus beer bong analogy. High pressure in a radon system is like drinking a Wendy’s frosty with a small straw; whereas low pressure is like chugging from a beer bong. Both can be appropriate depending on the context.
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).
*scroll down for more on max suction
What happens if I have no pressure?
It’s extremely rare that a fan is installed on a properly designed system and the system has 0″ of W.C. pressure. We call that “free air” and it means it is gobbling up all the air it can with absolutely no resistance. Usually 0″ indicates a system failure somewhere. 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 Pressure Field Extension (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. 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!
What is maximum operating pressure?
Maximum working pressure means the fan is pulling as little air as possible, usually 1-2 cfm. This is the upper limit of the fan curve. In our professional experience, we have found rare instances where a fan is “maxed out” and the radon problem is actually solved. However, usually when a fan is at max working pressure, the system is not mitigating radon efficiently (at least all 12 months of the year). Similar to having a car working at very high RPM, only this doesn’t stress out a radon fan motor like it would your car. If your fan is at max working pressure, please perform a long term test or purchase an hCRM to make sure that you are protected 24/7/365.
Can I stack my radon fans to get more pressure?
Yes, but you probably don’t need to. Read my full article on the subject here.
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