Very rare for today's furnaces to need a 6" flue pipe. Should be all double wall from the furnace through the roof with that brand's flashing, storm collar & cap. What's with the dryer vent?

What BTU furnace? I'm guessing 4" is fine if done right.

I would expect, the size that comes off the burner, should follow completely through to the top.

Obviously, one or the other of the techs, or both, are incorrect. I'd go for a third opinion.

A Rheem furnace is a good example of why you have to know the btu ratings in order to properly size it. All come off the top of the furnace with a 3 inch opening and if you go to the 125,000 btu furnace it has to immediately transition to a 5 inch vent. I'm guessing that maybe this 6 inch was lined with a 4 inch (hopefully doublewall) to terminate. We use old 6 inch flashings with 4" all the time. A picture of the setup would be helpful to pass judgment.

Okay DH and I think the tech was totally wrong. First of all, he was looking at the water heater vent on the roof because this is the furnace vent:

{{!gwi}}

I measured the pipe myself and it is a 5" diameter pipe. Here is where it comes out of the furnace and terminates into the attic ceiling:
{{!gwi}}


{{!gwi}}

And this is what it says on the pipe itself:

"TYPE B GAS VENT 1 IN. MIN. CLEARANCE TO COMBUSTIBLES . . ."
{{!gwi}}

The furnace is a Plus 80V model 315AAV and on the Bryant website it says it's capacity is 66k - 154k BTUH and doesn't say anything about BTU.

So, what do you think?

I've never seen a roof termination for a furnace like that in all my years....I see you are in TX but I still can't imagine that is manufacturer approved....the vent against the wood in your second picture is against any building code. B vent needs 1" from combustibles.

Isn't that just great.

Since this is a new construction house, I'm calling the head city inspector tomorrow and ask how his office managed to pass the HVAC with this pipe strapped to a combustible.

Thanks for noticing Tinmantu!

Are you sure the first pic isn't an attic vent?....I just can't believe that someone would use that as a furnace vent. It wouldn't cut it where I live because a 6 inch snowfall would bury it. Curious to hear comments from hvac guys in the south. Never seen such a thing.

No not an attic vent, we have ridge vents for attic venting. I looked at my neighbors roofs and they all have the same setup. The last time I saw a snowfall accumulation around here was 24 years ago.

Not an expert however in my experience I always go with a 6-in or better flu pipt.

The installation for the furnace will usually in great detail describe the proper venting for the device. I have an oil boiler which does take a 6 inch flue pipe, but i have not seen a newer (aka last 10 or 15 years.) gas installation which Uses anything any where near that size even it is an atmospheric vented furnace or boiler. I guess natural gas must be pretty cheap In TX as up north in order to save on gas most gas installations are condensing or condensing/modulating systems which vent through plastic pipe through the wall. They cost more but save a lot in a properly designed system.