Changed my mind about input air
 

Today, I didn't allow enough air into the basement while running the radon fan for 4 hours. 12:00 to 16:00
Ended up with more Radon! It was pulled out of the sump holes and cracks in the floor! I created a little vacuum and got punished. No Ham radio in the basement tonight!

The radon was low at noon. But I wanted to ventilate the basement to freshen up the air. I opened the pull-down stairs to the attic, thinking cool air would flow down. But it was so hot today in the attic, there was no down-flow of attic air. It was likely a suction effect. Especially if attic vent fan turned on (auto-on at 120F).

I'm going to need some way of bringing in outside air into the basement. When it's cold outside, that will be a real problem. I don't want a lot of cold air on the basement floor while the Radon fan is running.

~~~
On another note, I need to look at the Radon after the oil burner has been running! That thing sucks too!

Cheers,
Rich

I've seen a drastic improvement after sealing all cracks in the floor. The method of construction was to pour the basement walls, then later pour the floor. That left about a quarter-inch gap around the entire perimeter. I used a radon sealing caulk (from Menards) and sealed the entire perimeter. Since doing that, my levels are rarely above 2 or so. Usually in the 1 range. I think I'm almost nearing outdoor levels for most days.

Between the fan and the sealing, I've gone from almost 30 down to 1. Pretty awesome.

Just because I was curious, when we were out of town for 10 days, I turned the radon fan off. I anticipated not much increase, but boy was I wrong. Even with the sealing, it jumped to 17. Needless to say, keeping the fan on all the time now.

The Right Stuff
 

It sounds like you're doing it right. My old basement could be sealed with a lot of work. So it's not gonna happen.

I looked at the afternoon 24 hour plot and saw a 4.6 peak at 17:30. The oil burner ran from 17:00 until 17:20. (We are trying to make this tank last until WW3 starts) ;)
It's clearly sucking up some radon and shooting some up the chimney. I'll bet most of the houses on this granite hill do the same thing.
The good news is, two of the new families on my street have installed Mini-Splits during the last month. :)
The new kids next door went with Propane heat. They are already talking about moving to Florida (from MA).
I don't blame them.

I've wondered about all those oil burners you have in that part of the world. Any affect on the air quality overall in the area?

Looking at the New Cases (of lung cancer) map, it seems okay in this area. Not too bad..
https://www.lung.org/getmedia/381ca4...0-report-final