Hi. I posted a while back regarding how diagnostics allow us to use a 15 watt fan 97% of the time. For those of you who tried to connect with me I will be attending my first ever AARST conference in Bellevue in a few weeks. I'm co-presenting on Sunday a session called Gnarly Tales 2 where I have a 2.5hr slot to discuss how simple diagnostic tests can help turn a gnarly house into a nice house so you can go fishing instead of going back to put in a bigger fan. I really am looking forward to connecting with you guys and hearing about how you approach your jobs and also sharing my experience. Track me down and lets connect!

In my previous posts I was subtlety hinting that the design and documentation process we use in Canada could be adopted in some way in the US and that it might help lower your costs - smaller fan, decreased noise complaints, reduced call-backs, more referrals, added value etc. Adding the design and documentation components could be included starting tomorrow in the next mitigations that you perform and in a short while you might be able to see this added value pay you back real quick.
Frankly, discharging at the rim joist is not all that advantageous and is the less interesting aspect of the Canadian approach and is something that probably should not be considered without also taking the design and documentation and sealing approaches first.
Why? Well for one thing, having your fan outside and exhausted above the roof helps to hide the big noise footprint of using more powerful fans. When you take the "super-sucker 4000" fan and mount it inside the house you are asking for trouble. When the house is real quiet at 2am and that 100watt fan that seems not too loud during the day suddenly becomes intolerable at night - you will hear back from the customer - then what do you do? Install a smaller fan and retest? Isn't that backwards? Also, when that exhaust noise that you have been pointing up and into the stars suddenly gets pointed at the neighbor's house or in the backyard, it can also be too noisy. Mufflers help to take the edge off but they are not magic.
I'm not sure which came first the chicken or the egg - in this case but I feel that the design process that predicts the correct amount of negative pressure for each particular house goes hand in hand with the ability to install a fan indoors and the exhaust at ground level because the process helps to ensure that the smallest fan that can be shown to work is used from the start.
Along with this is also our guidance which says that we must seal "all accessible leaks". This is close to pure magic. I have fixed many homes that would require the "super sucker 400" only to allow me to use a 20 watt fan after a thorough sealing effort (which can take 30% of the time onsite). Sucking from a perfectly sealed container takes almost no fan power while sucking on a leaky container sometimes isn't even achievable with large fans.
Finally, exhausting at ground level has you competing for precious wall space. We have clearances to other openings, mechanical air intakes, corners, gas regulators, windows, and everything else that poking through the mechanical room wall. Often, we would have to first go into a garage or adjoining room to get the clearances we need and this can get real tricky. Or we're moving other ductwork that's in our way. Just poking through the wall anywhere and pointing up to the roof sounds like the easier approach in many instances.
My advice is to start with the design and documentation. Add this value which will get your profits up and reduce costs. Get used to spending a lot of effort sealing. Reduce callbacks. Start using small fans when appropriate (we are 96% 20 watt fans regardless of building size or soil material) and get the noise footprint down. When all that is second nature - go ahead and drop the exhaust to the ground - re-entrainment is almost a unicorn. But I think you will find the unintended (mainly noise) consequences of starting with ground level discharge to be not worth it if you don't do the other first.

One of the funniest friends I’ve ever had. Gone way too early. If someone you know is struggling - please reach out. I missed my chance.

Thanks Jeff - those are really thoughtful comments. I do want to clear up a few things so I don't misrepresent the "Canadian approach".
1- I did mention that there are engineer mitigators. But the vast majority of mitigators are ma and pa shops similar to the US. Why I mentioned it was that it shows that its a serious profession that attracts engineers and building scientists - which I think is awesome.
2-Since stack effect is a function of temperature - it's clear that you can develop a process where you measure the natural pressure under the slab and multiply by a correction factor to get a good estimate of the pressure under design conditions (not worst case but typical cold conditions) This is the most awesome part of our process because there is no guessing at the pressure you need to develop to fix that house. Like I mentioned, pressure change at the far holes is linear because it is laminar flow at the edges of the slab since the velocity is slow. So why move 3X the air to achieve a pressure target that the house already tells you is way too much. It's not more effective to be bigger than you need.
3-Extra paperwork - yes who likes paperwork. I mentor the majority of Canadian mitigators and this is a common complaint. But why not work smarter not harder? I use an app on my ipad that costs $20. I build forms that show all the relevant information a customer would want to see like: natural pressure - design pressure - pressure achieved fan on fan off - photos of all work like sealing etc. - piping photos - discharge photos - fan curve and system design (from pfedk screenshot)- hazard assessment - rough sketch of floorplan with test holes and suction hole - manometer photo - fan serial number etc etc. It can take as fast as 5 min to complete the form and pdf to client. Adding a huge value to the customer and taking a very small amount of time. Plus this is required in our standards. Could you take 2 hrs to complete on PC in the evening? Sure - but why not take 5 min onsite instead?
4 - question. You mention that most radon guys know how to do diagnostics. I was under the impression that you have no official design process. How do you know what your target pressure is for any particular house - I'm curious? A fixed pressure based on the height of type of house won't work.
5-I do take your point about the comparison of getting a ton of houses to at least 3.9 compared to getting fewer houses to 0.6. Its a good point that I don't know the answer to although awareness has grown by leaps and bounds here so maybe we can get the volumes up even without real estate transactions. Most mitigators I know are so busy and booking so far ahead we are already maxed out. I'm booking into May and June.
5- Ground level discharge - I don't know what to say. It seems to work. Bill Broadhead has an interesting story about this. Apparently the US would also have had ground level discharge if it wasn't for a one week delay in the results of a wind tunnel test that showed that ground level discharge without a 90 on the end eliminated re-entrainment.
6- Again happy to share the Canadian experience but as you point out your market involves so many different jurisdictions that what works here may not work everywhere without a shift in thinking.

I hope to come down to the States to see how things are done there first hand. And feel free to tag along with me if you come up here (Calgary Alberta). We can cross pollinate ideas for the betterment of both.

Hi Steven
The PFEDK breaks out the static pressure drop for both the soil as well as the piping at your design airflow and plots that on a graph so you can see which fan will overcome those pressures. The pressure drop in pipe is a squared function of velocity so the resistance really goes down to nothing at low flows and goes way up for high flows so it depends on the air flow needed. But if the design says you only need a small pressure change and that can be done with a small fan then that’s perfect. I don’t have much visibility for this but I wouldn’t be surprised if there is a tendency to overshoot the target pressure to the extent that a larger than necessary fan is being used. A US fan manufacturer once told me that he can’t figure out why they sell so many small fans in Canada and almost none in the US. Part of that might be because we have a design process. Plus, I recognize, we have all day to build a system so we can seal leaks or gopher in tight soils if needed. Our customers would not pay us for 3.9 - they want ALARA - As Low As Reasonably Achievable.
BTW you can access the PFEDK app online without buying anything and play around with it to see the impact of changing pipe length or pipe diameter on your design. PFEDK.app . Thing is, it may not make a ton of sense without having the device but I can give you some values to enter that would be similar to what you might see on a real job to get started. I also find if you email the report to yourself it makes a nice one page report that you can give to the customer in your report.
Also, I’m talking about the PFEDK because it’s easy and it works. Instead, you can download the chapter 4 I mentioned last post and do all the same calcs manually which is perfectly fine also.

Hi Jeff. In Canada we are obligated to perform extensive diagnostics on every job. Does it take a long time? No - with a fantech PFEDK it can take minutes to complete and produce a detailed report to support your design. The trick is that Canada has an official design process while the US does not. We measure the natural pressure (closed house) and multiply by a "stack effect" temperature adjustment factor to determine our target pressure which is different for every home. Takes 30 seconds. If we can demonstrate that amount of pressure change over the entire slab then the radon will be taken care of under the prevailing conditions and also in the cold months. The average post mitigation results from our last 1000 jobs is about 0.6pCi/L. It works. 97% of those are using a 15 watt fan as extensive sealing is also required. Is it worthwhile? Yes - since pressure change at the far test hole is a linear function of airflow, if the design says you need a change of 1Pa and you make a 3 Pa change, then you are moving 3X too much air and you are installing a more expensive fan than you need. Smoke doesn't tell you how much pressure you have so you don't really know if you have enough negative pressure or too much - maybe too much. Plus the cost,energy and noise penalty associated with the wrong fan. Mitigations in Canada are also more expensive - it takes one 8hr day for a job - not for the communications testing but for all of the sealing and optimizations to get super low levels and a quiet system. So a typical range across the country might be $2000 - $3500 and quite a few mitigators are engineers. The thing is that we don't have and nor do we want, a radon industry built around real estate testing where you have to be cheap and fast to survive. So while our design and sealing and documentation yields efficient, quiet systems and well-paid professionals, it may not translate down South unless you can get customers who recognize the extra value.

Even in a real-estate market where radon systems are really real-estate contingency-removal systems, the bottom line is that for the 5min it would take to use the PFEDK and our design process, you can show some extra value to the customer, eliminate call-backs, save money on the fan sometimes, make quieter systems and maybe make a bit more $$$ for 5 min worth of easy work. But everyone has to figure out how best to run their business and your market is different across the country so I'm not preaching - just offering another perspective that might help mitigators add value which means they can make more money in the right situation.

It's true though - I can't figure out why they would make you measure pressures if you don't have a process which tells you how much pressure you need. What's the point in that? Is -1Pa good, is -10Pa too much? Maybe its just baby steps but what you really need is a process that tells you what pressure you need to see for that particular house and then you can use the manometer to prove you can demonstrate that pressure. Did I mention Canada developed that process 15 years ago? Just steal our process until you can figure out your own. Download the Professional Contractors Guide and look up chapter 4 or contact me and I can send you a easier spreadsheet version. Or get a PFEDK and just use our process to determine the design pressure and the PFEDK to determine the system curve and print the report. It's super easy and adds value and removes risk.