It has been our experience that a significant issue with ice is not so much the pipe building up ice, but rather when the ice partially melts and falls into the fan housing. This will lock up the fan and cause it to get very hot and kick out on thermal overloads. The fan then cools down and tries to restart but it gets hot again since the ice chunk is still in fan housing. This cycle continues until the ice chunk melts out. This is not good for the fan and repeated high temps likely degrades the lubrication.
One approach has been to put one or two lengths of 3/8 inch stainless steel all-thread through a short length right above the fan. Use washers and nuts to secure it in place along with some caulk to seal it. If one looks through the short stub it looks like the cross-hairs of a rifle scope. So now when the ice chunk falls down, the bigger pieces get stopped before it hits the fan and it can slowly melt out.
Likely one length of all-thread is all you need for 3-inch pipe. And the presence of the all-thread does not degrade fan performance.

There are also pre-made devices with either venturi nozzles within them or a 45-degree directional change that can also preclude ice chunks.

Recognize that the air going through the pipe will be warmer than the outdoor air. 100% soil air would be at the mean annual temperature. Also, if there are slab leaks one is pulling in warmer, conditioned air. So, the air will eventually melt out the ice depending upon how cold it is outdoors.

Of course, this is not a concern in Canada as they have figured out how to install systems totally within the envelope of the house. But certainly, is a concern in North Dakota, Montana and Minnesota.

Thanks, Bruce and Bob: So, practice is exceeding code at least in larger buildings (I assume ICI is Industrial, Commercial and Institutional buildings, Correct?).

OK, we have heard from Canada. I ask the question again for our US based contractors: Is anyone aware of any jurisdiction that has adopted Appendix AF of the 2021 IRC?

Bruce:
Thanks for the input. I just looked at the City of Guelph's website and it read as though the mandatory measurement was only required when Option#1 (a Rough in System) was used but not required if Option 2 (soil gas barrier on walls and slab or Option #3 (soil gas barrier on walls and an active system)

MIchelle: The program on Sunday is a CE course and one can register for it through the AARST Symposium website. We are not able to accommodate auditors due to size of room and number of attendees so far.

I have been reading these posts and cannot agree more with the value of proper engineering, sizing of fans, area coverage as well as documentation. I also agree that changing a standard to what may be perceived as less stringent requires a cautious approach as Mr. Price has pointed out.

However, I would like to turn the conversation back to the original posting made by Mr. Weestrand regarding one particular point and that is the extension of the exhaust point from 2 feet to 4 feet above an opening in a window. This is not as trivial adjustment. It essentially invalidates previous systems that had been installed by practitioners prior to the change. It also adds one or two rungs that an installer has to climb on a ladder that can already be too high when compared to Canadian experience and studies conducted in Canada as well as those referenced and conducted by Mr. Brodhead, Turk and Lewis.

I echo Mr. Weestrand’s request for the data that the committee presented to justify raising the height of separation from an opening when the discharge is directed upwards. Presumably, there would be a preponderance of data and opinion that would cause the committee to make such a change and Mr. Weestrand’s request for that data to be shared is reasonable and in line with the transparency that characterizes this organization.

Doug Kladder

Kevin:

Kudos for taking the time to listen to the interview.

Here is a Dropbox link to the Hopke paper referenced in the Technical Bulletin that you were asking for:
Hopke Paper

I also am providing a Dropbox link to the Technical Bulletin as I have been told that the original link I posted in the Listserve is not working with all browsers.

Technical Bulletin-18


I totally agree with your assessment that air cleaning is a good Trim technique. We have worked with a number of filters and have found that a whole house air cleaning system is preferred rather than console units that treat a single room. It is quite amenable for commercial builingd with large HVAC systems and where better filters would improve other indoor air quality concerns. Also, a HEPA filter is the least desirable as it not only creates too much pressure drop for blower but also has a more dramatic effect on increasing the unattached fraction. Actually, the lower MERV 8-10 filters reduce total WL and with minimal impact on unattached fraction. This is a case where a less expensive filter is preferred. So, for those that may be considering this approach please do not consider “true HEPA filters.”

Doug Kladder

The question regarding the impact of air cleaning devices has arisen a number of times over the years. The answer to that question has also evolved as the dosimetry models have become better at allocating dose to various particle sizes.

Rather than adding a lot of verbiage into a posting I am attaching a Technical Bulletin that was prepared recently for an agency that was interested in radon decay product reduction in an occupational setting. Although the setting is occupational the substance of the article is transferable to other building types. It is also a bulletin that we had some SMEs review, some who also participate in this ListServe review. I will let them share their opinions should they choose to.

Included in the bulletin is a link to an interview we did with Dr. Hopke who has done much of the research on this topic where we discuss air cleaning as a trim technique for active soil depressurization. I paste it below for convenience.
Dr. Phil Hopke Interview: Hopke Interview

I will say this that air cleaners do not reduce radon, as has been pointed out by others, but they do reduce radon decay products. The reduction of dose is not as linear as is achieved by radon gas reduction via active soil depressurization, but nonetheless is a reduction rather than an increase in dose.

Doug Kladder
Colorado Vintage Companies

This has been an interesting discussion as it falls into the category of questioning one’s assumptions and focusing on intent rather than habit.
Coming from the chemical processing industry it was always best to measure the variable one is attempting to control rather than a surrogate. In our case we are trying to control radon/RDPs. In the early years of this industry, radon monitoring equipment was expensive and did not provide a cost-effective means for direct monitoring of the key variable-radon. Hence a surrogate measurement of pressure was used. As many have pointed out in this thread “things have changed” and direct radon measurement has become more cost-effective. Furthermore, the use of consumer monitors will likely point out subtle deterioration of system performance more readily than a U-tube will.
The last point is made based upon experience of our students who began calling when homeowners acquired consumer CRMs that were showing elevated radon levels after a system had been installed previously and validated with a short-term test. After retesting with an approved short-term test device, the houses were indeed above 4 pCi/L even though the U-tube still showed the same vacuum. The logical explanation was that the original mitigation system likely never did fully reduce the levels but post-mitigation testing was faulty due to home seller non-compliance of testing protocols or testing during low radon entry periods.
Regarding 100% outdoor systems, this situation presents itself in the Rocky Mountain West as there are many homes where the drain tile is outside of the house and there is no internal sump to connect to. This is common with hillside houses where gravity allows surface water to drain down the hill without the need for a pump. Also, the lower levels of the home are walk-out and fully finished, therefore making a floor core a rather unsightly conversation piece. Hence, many systems are installed completely outside of the house and connected to the exterior perimeter drain. This presents a problem with pressure monitoring style performance indicators due to condensation in the connecting tubes. This can be solved in at least three ways:
1. Diaphragm repeaters that preclude moisture from the gauge (more costly and not too practical)
2. Ammeter style indicator on power to fan. This technique is incorporated into the low voltage systems manufactured by PDS. The current flow is proportional to the air flow in the system and the current can be used as a surrogate provided the meter face is redesigned like a “idiot gauge” on a car. This is especially workable on the secondary leg of the transformer.
3. Measure the radon inside of the house with a consumer grade CRM as an indicator, with an elevated reading being the impetus for verified measurement.

I trust that as the standards committee evolves that it will expand the allowance of methods that address the intent of a standard such that innovation can occur from both the practitioner as well as the innovator/scientist/engineer.

Doug Kladder
Colorado Vintage Co.

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

Thanks, your experience matches others, as well as my own. The problem can occur where a passive RRNC system is to be installed. Appendix F does not require the poly to be sealed to walls. If a conscientious builder decides to go a little further and seal the poly but still stay with passive system one could have ballooning issues. If on the other hand if poly was not sealed and merely brought to edges as stated in App F then if it had to be activated it would be difficult to seal to walls without the use of extension strips, replacing poly or not bothering to seal at all.

I agree with all comments that adding the fan from the beginning solves a lot of problems, but it is almost as if one would recommend NOT sealing poly if a passive sub-membrane is to be used.

Doug