tmurf.1 wrote:

The radon should be well below 4 pc/l...

So you might buy a few test kits and turn off the fan, then run it 12 hours
per day if it's more than 4, then 6 if it's less than 4 or 18 if more, and
so on. With noise as the issue, you might replace the fan with a long-life
light bulb at the bottom of a tall chimney.

The EPA says a non-smoker continuously exposed to 4 pCi/l has a lifetime risk
of dying of lung cancer of 73 in 10,000, ie odds of 139 to 1. At 1.25 (close
to the 1.3 average indoor level) it's down to 23/10K, ie 435:1. At 0.4 (the
average outdoor level), it's 23/100K, ie 4,348:1. So why stop at 4? Will an
electronic air filter help? The EPA plans to do more research on that.

The NSC gives 2:1 (men) and 3:1 (women) odds for contracting heart disease,
3:1 for contracting diabetes, 228:1 for death as a car occupant, 1,310:1
for death by medical complications, 4,857:1 for death as a bicyle rider,
12,417:1 for legal intervention involving firearm discharge, 55,597:1 for
death by legal execution, 56,439:1 for death by lightning, 286,537:1 for
ignition or melting of nightwear, 372,498:1 for death by contact with
venemous spiders, 413,887:1 for death by flood, and 1,241,661:1 for death
by contact with venemous snakes or lizards.

Nick