reasons for mounting the fan and exhaust piping outside building envelope in US Indeed, this has been an interesting discussion and one that has come up every two years going back to the beginning of Bill Field’s Listserve. Allow me to pontificate as I have been involved with this all the way back to the original mitigation standards.
The purpose of having fans outside or in the attic is to prescriptively reduce the potential for the leakage of radon laden air into the occupied space for two reasons: 1.) Leakage from the fan housing and 2.) Leakage from poorly connected vent pipes on the discharge side of the fan. During the late 1980s and early 90’s fan housings and passage ways to the electrical handi-box could and did leak. Also, people were using sheet metal rather than PVC piping, or if it was PVC, some were using thin wall pipe that even a moderately 5 year old with an attitude could break.
If we fast forward to present times, fans that are considered to be “Radon” fans have definitely improved since 1991. Also current standards cite the use of schedule 40 PVC or ABS as Mr. Wood has pointed out for years as being the appropriate thickness.
Yet, we still occasionally run across installations with non-compliant piping and hear anecdotal stories about installers not gluing their pipe. So the question comes down to: Do we have standards that guard against non-compliance and poor workmanship, or do we recognize advances in the fan industry and assume compliance with minimum standards?
One recommendation might be that a standard be developed by the fan manufacturers that specify what a radon fan is. This certainly would address several elements such as moisture resistance, UV resistance, electrical, etc., as well as leakage. Without a prescriptive fan standard I would assume that fan manufacturers would be reluctant to guarantee 100% leak proof, but rather meet and verify a maximum leakage rate that would not present a significant increase above background (0.4 pCi/L).
The second aspect would be verification. Going back in time again to the early years, tests were often deployed on multiple levels of a home rather than in just the basement. This more thorough testing identified re-entry problems that led to the current prescriptive approaches. However, today’s approaches only test the lower level and hence do not pick up higher measurements upstairs that could result from disjointed pipes or improperly located discharge points.
Fast forward to today, we have relatively inexpensive consumer testing devices that although not necessarily approved for certified tests do a pretty good job of identifying problems.
So, consideration could be given for alternate approaches if additional testing and surveillance measures are employed.
As far as discharge points, I look forward to additional data from Mr. Lewis and Mr. Turk, assuming they are continuing with the study in New York, but preliminary results appear to agree with what our Canadian friends have observed.
Doug Kladder