Radon system causing slight backdraft

cwilliams2000

I recently installed a radon system. The radon was fairly low 4.6 at the test and my house has a french drain feeding into my sump pit. I fabricated a lexan cover with a gasket sealing it to the sump and the vent pipe draws from the sump. It seemed to work very well and I had planned to test in a few weeks to confirm it has helped.



But...



This morning I noticed that I could smell the faint smell of exhaust in the room. When the system is running there seems to be no issue.



However when it sits for several hours and almost cools down completely there is a slight backdraft, so what I am smelling is the scent of the pipe.



I am looking into reducing the radon fan speed to help since I don't think I need that much output and I checked all the seals on the system and none are actively pulling in room air, but I did see that in the boiler room the gap between the floors and walls is pulling air slightly. So I will be calulking those gaps tonight hoping that it may help.



It does appear that it is only slightly pulling air through a cold chimeny but I would obviously like to avoid it and it would probably get worse during the einter as the house is closed all the time.



Have you run into this issue before or have any thoughts?