Yes, but with modern fan technology it’s almost always unnecessary.
What does radon fan stacking do?
Many DIYers think that more power is always the solution to their radon problem. It rarely is. Proper system design and pre-diagnostic testing is the key to a properly functioning radon system.
Radon fan stacking, when done correctly, should increase the vacuum-pressure
on your radon system. Imagine you’re in a tug of war and at a stalemate. This tug of war is with the ground and it just won’t give up that soil air. When you add another radon fan–properly–it’s like doubling the size of your tug team and you hopefully win that battle.
Stacked fans cannot increase the total maximum airflow of a fan. So if your manometer reading on your system is below max working pressure for that particular fan (see the fan curve image to the right), then stacking will do nothing but increase your noise level and utility bill. Read this article to understand fan curves. Fans pull as much air as the system resistance allows.
Which fans can I stack?
You can only stack “like” fans, as in: the exact same fan make and model. Don’t go buying cheap stuff off eBay or using an old fan from a neighbor. When you stack two different model fans the different air flow rates cause turbulence and create dissonance. Oftentimes, all you add to the system is noise. You will almost never improve the system functionality. If you see two fans stacked that are two different makes/models, then you know someone is just throwing you-know-what at the wall to see what sticks.
Why stacking is no longer used
Since radon fan stacking only increases your vacuum pressure, it’s not normally a good solution. Modern fans like the GX5 Pro or the extremely popular Rn4-4EC by Fantech have very high maximum working pressures. So high–in fact–that these fans have been known to suck the oil out of manometers!!
Pre-2017 the average inline fan would max out around 2″ of water column pressure. That made clay soils are other tight soil jobs difficult. Fans that could routinely get over 2″ of suction were specialty fans that either: didn’t last very long or made a tremendous amount of noise*. Fans like this still exist but you won’t find them on our site. We only want to sell the best performance and not saddle you with warranty issues down the road.
In 2017 Fantech debuted the Rn4EC fan which routinely got over 4″ of suction (4.3″ max). This blew the top off the industry. At that year’s international radon symposium, you would’ve thought they won the Superbowl with the amount of hi-fives and “atta-boys” their team got. Since then, other major fan manufacturers have raced to catch up and at times even exceed the max pressure of that fan. However, in my talks with pros, the Rn4 still holds the torch for best performance, energy draw, and sound considerations. If you need more than 4″ of suction then—in most circumstances—you need to go back to the drawing board and rethink your system design.
*Not all pre-2017 high suction fans are “bad buys” and not all modern fans are “good buys”, this is simply a generalization of where the market was at and what most contractors at the time thought. At PDS, we’re proud of our fan offerings and stand behind everything we recommend.
System Design Considerations: when do I need high suction
The most common reason someone is thinking of stacking a fan is because they didn’t put in the legwork to design a great system. Suction pit systems, the most common systems people try to stack fans on, require a minimum of 10 gallons of dirt/debris removed from the pit. 15+ gallons is ideal. I’ve seen folks get upwards of 30 gallons or six home depot buckets out of them and they performed incredibly well. The more debris that is removed, the better your pressure field will be, the lower your suction, the higher your airflow, and the lower your noise. Sweat equity pays off. Watch our tutorial video here and make sure your radon professional is not skipping out on the hard work.
Radon suction pit extraction point location is a huge consideration as well. Untrained pros will put suction pits in the center of the slab. This may seem like a good idea but it’s just the opposite. Center slab has the most compacted (i.e. tight soil) which has the least airflow. Corner and edge placements let you tie in to a natural air pocket that continues around the entire slab (see our video above for sub-slab footage).
PVC size can dictate your airflow. Read my article on why 4″ should be in your design.
How do I stack fans?
If you’ve gotten this far and you truly need to stack, please consult with a pro. If you are a pro, here’s how:
Again, the fans must be the exact same make and model. Rn4ECs at this point, I recommend.
It’s recommended that you secure the PVC very well on both sides of the system. You’ll need a 6″ x 6″ coupler for the center stack between fans. If fan weight is an issue and you cannot secure the PVC weight well, then you may need to remove the LDVIs and switch to hard reducer boots. Stacking fans already increases noise and removing the LDVIs will do so as well. Prepare the homeowner for this inevitability.
Run both fans at maximum speed at all times. Any change in speed will cause dissonance issues and negate the benefits.
Do not put fans away from each other inline, or tie in fans to the same suction point but with multiple PVC runs. Fans do not work to boost each other if you put one at the top and one at the bottom. There is no evidence that additional fans on the same system will do anything to improve system functionality. Only rarely does a one-on-one fan stack improve the system flow, and in that instance it must be executed exactly as described above.
Conclusion
Is your fan at max pressure? If not, stacking will not help.
Is your suction pit big enough? 15+ gallons. Tools and techniques matter. Watch our video above. Use the suction pit pro. Use an auger. Get dirty and work hard.
Do you not have a suction pit? I’ve almost never heard of a need to stack fans on an RRNC system, sump system, crawlspace system or other traditional system type.
Is your water table effecting your suction? What else could be inhibiting airflow? Intermediate footers, floor drains? Look for the problem first, don’t just throw more power at the situation.
The true radon problem will reveal the actual solution.
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