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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Jack wrote:   "one of the best demo videos of combustion safety test performed by a BPI certified guy you can find online"

The best you can find online?  How good does that have to be?  I'll grant that the production values are very good.

As for your concluding question, even an induced draft must be proven superior to the worst case conditions.

I'll come back after reviewing the video I paid for.

More precisely, in order to conform to the appliance in the video you referenced, fan-assisted draft, power burner type (fan located at inlet).  According to Krigger & Dorsi,

"Most fan-assisted heaters are vented into vertical chimneys and their draft fans have little or no effect on the atmospheric chimney draft. When a fan-assisted 80+ AFUE furnace or boiler is vented horizontally, the draft in the stainless-steel vent is positive.  The positive-draft vent must be substantially airtight."

I still haven't gotten to my video, but I've noticed that BPI allows drilling holes in such (Category I) vent designs.  Category IV, direct vent and power vented designs must be hole(s) free.

http://www.youtube.com/watch?v=7A7sExbFO8w

 

In this one he drills and tests a PVC flue. 

 

I've read a number of debates about this topic and rarely come across anything I'd hang my hat on. The vent pipe manufacturers will apparently all tell you not to drill their product. I've heard a few descriptions from seasoned techs about how to plug drilled holes in various types of pipe. Some states have licensing for HVAC contractors that doesn't allow a non-licensed person to touch a furnace or water heater. It's a can of worms...

The appliance in the video is not " power vented " , but is " induced draft " ,or " fan assisted " meaning Category I according to NFPA 54

(Cat I = negative pressure in the vent pipe , non-condensing ) This should not be a problem when drilling a test port properly.

Cat III or IV vented appliances are under positive pressure and the integrity of the vent pipe should not be breached unless you are prepared to replace the section or fittings that were opened and then re-test the ambient ..

Great question.

 

BF

Blaine, you beat me to it. There is a huge difference between a positive pressure Cat IV and a negative pressure Cat I vent system. With the Cat IV (positive pressure, PVC vent) there is condensation and some of the condensation is corrosive due to the other gases condensing as well as water vapor. If a test hole is drilled, and the seal is compromised in any way the flue gas will leak into the CAZ which is usually in the basement and the stack pressure will carry the flue gas through the house.

The best way to resolve this would be working with the manufacturers to install a test port in the furnace cabinet that we can utilize for testing.

Thank you very much, guys, your answers are very helpful.

It looks like we've figured out the CAT I versus III&IV concern --good feedback. 

 

I had to go watch the youtube link (pt 1&2) in Jack's question and, while it was clear and informative, it was incorrect on more than a few things.  For example, at 3:04 he incorrectly states that an induced draft furnace does not need to be checked for spillage. Per BPI Building Analyst standards p. 10, "Induced draft heating systems shall be checked for spillage at the base of the chimney liner or flue.  If a chimney is shared between and induced draft heating system and a natural draft water heater, spillage shall be checked at the water heater draft diverter." (emphasis added)

At 4:40 he just "calls it" for the CO levels versus checking to see if CO levels have leveled off or are still rising.  He must check to see if CO levels will continue to rise; if they exceed 100 ppm, then he must amend his workscope per BA standards p.14

 

I think both draft and CO of the furnace could have been checked from one port (his draft port); it would still be undiluted flue gas.  I could go on but it sort of feels like work.  If they post my comments to youtube maybe I'll continue.

I have to disagree with you on using those plugs. Cat IV PVC flues are pressurized and need to be sealed. How do those plugs seal into the hole? Are they glued in? is there a problem with the fact that they are a lighter, thinner material than the PVC? What kind of life span do they have in a moist, acidic, pressurized pipe?

 

This isn't hard, when there is PVC exhaust vent, you simply go outside to the vent termination and test the appliance. Simple, straight forward and reliable and you avoid any issue with drilling PVC vents.

I hadn't seen those before, but they look like they're intended for plugging holes in metal ductwork after taking pressures.

I guess I can't see why one cannot go outside and test at the vent terminal. Then there is no question about drilling PVC vents. I'll sleep better that night knowing that I didn't drill a hole and leave a compromised vent which could have the potential to fail and cause an indoor air quality issue at some point in the future.

Blaine & Chris have noted what should have been obvious to anyone considering testing mechanical equipment.  Although many states may not require licensing for this procedure one should not attempt without the highest confidence and training.  If you are not sure how to go about testing, what are you going to do with the results when they show that adjustments to the burner, gas valve or venting need to be done? I suggest hiring a competent service tech, leave it to the appliance professional.

 

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