[Xringer]

That "inline centrifugal fan" looks like the type I'm using.
One to bring air down from the attic to the basement stairway and the second fan
lifts cool air off the basement floor and pumps it out to a 'dryer' vent.
I normally don't turn on the basement fan, unless we get over 4 pCi/L on the Radon meter..

Did a test this week on my kid's new home. Basement has 22.0 pCi/L (picocuries per liter), 1 foot above the sump pump hole.
Gonna do some testing on the 1st floor starting today and retest the basement at the same time.
It takes 3 days to get a reading, after resetting the old data.

22.0 pCi/L is worrisome to say the least..