250 cfm differential with radon fan: Why?
Hi. I am working on a continuing problem, and hope to get the advice from the smart minds on here to figure out why we have are having both indoor humidity fluctuations and elevated radon ( GBA links to both topics attached below). Trying to solve both humidity fluctuations and elevated radon ( 9.3 pCi/L) with radon fan running. I did close up the 3 small HVAC supply damper vents as suggested in the previous post ( see link below)… thanks! However, we are still having pressure/cfm differential with the radon fan running, based on blower door test done yet again. The consensus on here has been to look at sealing-at that MUST be the issue. I agree, since the radon system is supposed to be separate from the home and crawl space-located beneath the vapor barrier and terminating above the roof line. I noticed one of the advisors on here mentioned the vapor barrier-which I never considered before. When I looked closer at it (12 mil. guardian liner), I noticed it has multiple pin pricks/tiny holes throughout out the crawl space ( 3400 square feet), damaged from the sharp , uneven gravel beneath. Could this be the possible answer to all our problems with pressure/radon and humidity????
Just to recap, we have an encapsulated crawl space (house built in 2008) with closed cell foam on foundation walls ( open cell on rim band), 12 mil vapor barrier, ducted Ultra Air Dehumidifier with radon piping installed beneath vapor barrier as a precaution. Home tested 1.0 pCi/L before encapsulation. After crawl space was encapsulated radon test came back at 10+pCi/L. We then added a Radon mitigation system ( fan) to the existing radon piping installed beneath the vapor barrier. Immediately after the radon system was operating we noticed a significant increase in indoor humidity. In addition, the dehumidifier in the crawl space was now working/operating 24-7. We realized that if we turned off the radon fan, the home and crawl space humidity were immediately impacted (see 2nd link below on humidity and radon fan). After determining the radon fan was directly affecting humidity, we had a blower door done with both the radon on vs off. Just as we thought, the radon fan was affected the pressure-cfm was 250 less with radon fan on. Additional sealing was done on the vapor barrier seams ( which were gaping and open in multiple areas) with mastic. We had hopes this would solve the problem.
Two months later, we did another follow up radon test, and we were at 9.3 pCi/L with the radon mitigation system running. We then had diagnostic testing done to help determine what and where the problem might be. A blower door test was done again and the results were:
2554 cfm with the radon fan on
2789 cfm with the radon fan off
In addition, pressure testing was done on the radon piping which is beneath 12 mil Guardian Liner ( vapor barrier). Pressure test revealed pressure was good at pipes nearest to start of system (fan located outside), and decreases significantly to only provide suction to the first third of radon piping.
I am at my whits end… have been told they have sealed all they can, and don’t know what else to do. I am left with both a radon and humidity problem-which I think are both related, especially considering the cfm differential. The advice on here mentioned to look at the vapor barrier and sealing. The contractor seems to think the pin pricks located throughout the vapor barrier ( which is on top of sharp gravel ) is not an issue.
Apologies for the long sordid story…appreciate any thoughts/ideas??????
Thanks to all!