Wye in vent connector

I’m in training and saw this during a mock inspection. Is this type of assembly allowed for natural gas appliances? They both seem to be using C vent tied to the wye going into the chimney. Also, the stickers on the unit next to the vent appear to be too close for C vent. I didn’t see any signs of back drafting on the water heater. Anything else I missed? Thanks!

You may want to continue with your training more before you do any more mock inspections. I recommend the plumbing and HVAC inspectors class so that you better understand what you are inspecting. You will be glad you took these classes when you inspect full time. I don’t know what C vent is but I suspect you are talking about the flue pipe.



I know two systems using common venting can join together at the same level connected to a vertical chimney. However, the above photo they join together horizontally. IF that is a vertical flue inside the wall, I would expect to see two holes in the block, furnace flue entering low and water heater entering higher?

Brian this is the way it’s been done for decades in some parts of the country.


Sorry. Which way? Higher, lower or parallel?

Two flue pipes entering the chimney in a single penetration.


2 into 1 then into the chimney is common in my area although it’s becoming less common since nearly all of the furnaces these days are high efficiency and utilize PVC. Despite that, upward slope must be maintained and that install doesn’t appear to have that.


I agree Matt. I have a feeling a taller water heater may have been installed at some time. There should be a 6” rise on the water heater flue before the 90 elbow.

Good idea to go back over the classes. I didn’t see this particular configuration in my first run through. I definitely have a lot to learn and need more hands on experience. I guess the student forum would have been a better place to post the question. Thanks.


You’ll never stop learning.


Nope! Learn from those in the know. Not from those still learning. Your question was fine. then again, we’re all still learning. :wink:


You’re referring to the slope of the wye fitting, right?

Also, would the insulation on the A/C line and the plastic and paper stickers on the equipment be considered a combustible material that would need 6" clearance from the single wall flue pipe?

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Really, all of it. The pipe and fittings must continue to rise at a minimum of 1/4" per foot.

I consider any insulation, sheetrock, stickers, etc. to be combustible. I know it can be debated that sheetrock is used as a fire barrier so how can it be combustible. My local gas company calls it out this way when they do inspections to turn service on after a disconnect or a safety check for some other reason. So, with them to cite as a source I don’t get questioned

It would be a good idea to see how things are called in your area. As inspectors we’re often in kind of a, “no-win” situation. In one area you will be called blind and incompetent for not calling something out and in another area for same issue you’ll be called an alarmist and inaccurate.

Along those lines Martin mentioned the 6" rise in the flue above the tank. I’ve seen this argued for pages and pages on other forums and my biggest takeaway is that it’s a regional thing as well as a manufacturer’s spec thing. In my area the city inspectors don’t enforce that so it’s just not a hill I’m willing to die on.

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I would have to agree Martin. Possibly upgraded from a 40 gallon to a 50 or 60…

Speaking about the vents @amall , I would be more concerned with the unsealed connections, especially the ones that are circled. The one on the left is barely connected.

And there you have it. I was once told “You should learn something new every day, no matter what it may be. It keeps the most important organ in your body functioning.” Happy schooling! :slightly_smiling_face:


I like the way you highlighted those areas and used arrows. Is that part of your inspection software?

And yes, that joint on the left is particularly bad. I counted the screws at each connection and they all had three. Nothing felt loose, either, but that horizontal section is barely hanging on. What kind of sealant are you accustomed to seeing? I’m guessing you’re referring to high temp flue tape and/or high temp silicone?

I did notice there was no CO detector on that level, which I made sure to highlight in the mock report.

Thanks again to everyone for all the insights!

I downloaded the picture and used PhotoScape X to add the arrows. It’s a fun photo editing software to play with and fairly easy to learn.

Aluminum Tape, Silicone, and high temp mastic. The mastic is applied with a cheap paint brush.

Good catch! Always check your local regulations when looking for CO detectors too, some AHJs have very specific requirements for them.

Good luck to you!


In a natural draft (negative pressure in the flue) exhaust, the connections are only to be crimped, joined, and held by 3 screws. They are not to be wrapped by homeowner special tape or whatever. That is a mistake homeowners make. Once draft is established, the flue draft is sucking (yes, sucking) the exhaust out of the house. There is not enough negative pressure inside the flue to cause any type of ill effect by unsealed joints. The silly, and unnecessary, tape only makes it for a swearing episode while the tech disassembles the joints for servicing. PLEASE do not add any tape or sealant to those joints!



Ok, good to know. Thanks for the correction.