High radon after installation of whole House fan
When we bought our house (built in 2012) it had very high radon (in the 20s) so I installed a sub slab system which consistently brought the readings down to around 1. We later installed a whole House fan that we run only when many of the windows are open and our radon has spiked into the twenties again. I have sealed the basement walls and floors and caulked all visible cracks and penetrations, and installed a higher flow rate radon fan (Fantech Rn4-4EC) but the radon readings have remained stubbornly at around 10.
Other information: poured slab and foundation walls, single penetration radon system, basement has sub slab French drain system.
Do you y'all have any ideas about what else I can do about this? We would really like to continue using the whole House fan, if possible.
Thanks so much!