Proper means to "plug" flue pipes after testing gas appliances.

I have seen metal "plugs" (and this may not be the correct term) used for the holes that are drilled in vent pipes, in order to test combustion appliances.


I'm referring to the type 1 vent pipe that is standard for atmospherically-vented gas appliances.


These plugs appear to be superior to HVAC foil tape. Any thoughts on this?


Also, does anybody know how to get their hands on these metal plugs? I use a 5/16" bit to drill probe holes.


Thanks in advance!

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Thanks David.


The issue for me still remains whether a quality plug for metal and high heat applications exists. The plug referenced in the discussion from a few months ago was a plastic plug, and therefore it would not hold up under flue gas temperatures that average 300 - 400 degrees.


The search goes on...

I know that we don't want to raise any questions from our customers about holes in their flues, but if there is a negative pressure inside the flue, do we HAVE to seal it?  As an example, a conventional gas water heater has 15-20 in2 of opening at the draft hood, and we are just a few inches away from there with our 5/16" diameter hole with less than an additional .1 in2 (one tenth of a square inch).  We use 181 tape and won't feel bad if it falls off - we have never gotten a complaint about this happening.  If you feel you must plug this hole, screw a short stainless slotted head machine screw into the hole, adjusting the drill size to make this easy.  YMMV.

Ed Minch

Thanks Ed!


I hear where you're coming from, and I can't think of anything against the point(s) you have raised.

I use the snap in metal plugs. In a previous life, my work in service & installation management-in particular when it came to NFPA situations and the like-  taught me that if you make some sort of modification to a product, you must make a suitable good faith effort to keep the product within the standards intended by the manufacturer. In this situation, I interpret that to mean when drilling a hole in metal for a test, it should be plugged with metal. 

There may be some legal line of reasoning behind this as well. An inexpensive metal plug that is sized properly will leave the homeowner with the impression of the mark of a well-equipped professional and may also avoid a potential liability claim. I have met some homeowners who look for the smallest reason to stir up trouble.  

Thanks a lot Bruce. That's good perspective to have.


Here's a link to the metal plugs I use for single wall metal flues. Recommended by my BPI training provider. They have worked well for me. Sorry, there's no picture of the product on their site.

Downside is that the price doubles with shipping charges when you order a single 20 pc bag. 

  a-386, 5/16" hole plug


Hope that helps!

Thanks a lot Jeffrey! I think you hit the nail on the head.



No problem.

Forgot to mention, but it helps to have a flat file with you to clean up the hole from the drilling when necessary.

Be careful with HVAC metal tape may are not rated for the heat a flue produces.

I realize you are looking for a manufactured plug, but good old fashioned hi-temp. silicone always does the job. If Josh Lloyd sees this, perhaps he can chime in on pre made hi-temp. silicone plugs which are used by the program he works with.


Remember that ALL silicone is hi-temp.  If memory serves, the clear is 580 degrees for some amount of time, and the colored stuff is 20-30 degrees better - red and black being the best.  Just make sure to use pure silicone, not something like acrylic latex with only some silicone.

Ed Minch



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