WH draft hood to Class B vent pipe: C to B connector required?

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WH draft hood to Class B vent pipe: C to B connector required?
Author: Plumb Crazy (CA) If wanting to use double wall Class B vent pipe for natural gas 50 gallon water heater, is a single wall to double wall C to B type connector necessary? Or is it fine to just fit the B Pipe directly over the included draft hood of the water heater, screwing that connection only, while the rest of the B Pipe stack is twist locked?
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Re: WH draft hood to Class B vent pipe: C to B connector required?
Author: hj (AZ) either way is fine.
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Re: WH draft hood to Class B vent pipe: C to B connector required?

Author: Plumb Crazy (CA)

I ended up using a C to B appliance connector, as I found a technical service bulletin from the water heater manufacturer (AO Smith) advising this requirement, with no explanation as to why they require it. I always follow the manufacturers recommendations, but still, it would be nice to understand what benefit the C to B appliance connector adds to the installation.

The issues that come to mind are that the single wall portion can be more easily screwed to the draft hood, whereas screwing through B pipe can lead to pipe wall deformation and distortion, causing exhaust gas leaks, and making for a sloppy install.

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Re: WH draft hood to Class B vent pipe: C to B connector required?
Author: hj (AZ) Absolutely NO benefit.
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