Drilling through a flue pipe of a power-vented combustion appliance

Here is a dilemma for a BPI-certified building auditor - should I or shouldn't I drill through a flue pipe of a power-vented combustion appliance? At first it seems obvious - don't. The BPI standards state that clearly. However, in the industry I see a number of people do that anyway. And even one of the best demo videos of combustion safety test performed by a BPI certified guy you can find online shows him drill through it in TWO places, without even a sign of doubt or concern on his face. Also, some government financing programs require you to gather that data that you can't get otherwise (sticking the probe from the outside into the chimney is not an option). 

Another question I see coming up is - since there is fan pushing those combustion gases out, wouldn't the pressure in the flue pipe be greater than the CAZ pressure? 

Would appreciate your experience on the matter.

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Eric, I am BA, Envelope and Heating BPI Certified. I have quite a bit of experience in HVAC. Some of the adjustments I could make, or I would either refer the homeowner to a HVAC tech or provide a service tech for them if it was a unit that I did not feel competent to repair. In NY where we have a very active Home Performance programs running, this has not been an issue or should it be. There is a great difference between placing a probe in a flue gas stream to measure vs. making repairs and/or adjustments.

To get back to the topic, BPI appears to be against the idea of drilling power vented (CAT IV, PVC vent). The reasons to not drill are the same as why the radon fan is outside the house and the pressurized part of the system is not allowed to go through living space.

I agree with you about the confidence and training.  I'm unclear on what level of combustion testing you would advocate for the BPI BA or Shell/Envelope person and if the current standards are allowing too much.  The scenario you gave (assuming compliance with the current BPI standards) about the testing results is addressed in the BPI standards  Adjustments, if required to be part of the work-scope, are required to be performed by a Heating, AC/Heat Pump, or other applicable BPI-certified person or, if performed by a non-BPI-certified applicable specialist, it must be approved by the appropriate BPI-certified specialist.  In other words, the BA and Shell guys are required to enlist the services of a more qualified professional.


I think the theme here is what should and what shouldn't the bazillion auditors out there be testing.  Everybody is trying to get on the same page about even the requirements of the existing standards.  As new standards come out and existing ones (hopefully) evolve, we need as much consensus on the do's and don'ts.  Surely we can come up with acceptable boundaries that will be safe and beneficial for all concerned.


As a BA and Shell/Envelope certified person, I don't drill PVC, B-vent, stainless steel or any positive pressure venting system.  I am still concerned about potential results of missed testing opportunities and wish there was an approved procedure that would allow the testing.  The limitations of many scenarios prohibit some folks from accessing the exterior vent openings; ladder or roof work may be necessary and not possible due to weather or other liability concerns.


I find it hard to believe that resealable test ports are not a requirement for all installations.  Wouldn't this be better for everyone?

As far as I can tell, the intent of the BPI standard is to determine whether or not there is negative CAZ pressure, and whether or not atmospheric draft appliances are burning cleanly. Checking out typical 80% equipment is quite easy and I don't think it creates any issues. If TWO things go wrong--a vent that's being backdrafted, AND a burner that's emitting a high level of CO, you have a possible disaster. With newer sealed combustion equipment the likelihood is very low, but there can still be issues. 



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