1940's chimney with "extra connection"

[ejager]

This 1940's home had the original brick chimney with 'terra-cotta liner'. Only a furnace and water heater using the chimney now - separate issues. 

What I am curious about is this 'side-elbow'. Any thought would be appreciated.

 

 

[Jim Katen]

Does it actually connect to the chimney? 

What's under it? 

I've seen people plumb kitchen ceiling exhaust fans into chimneys, wrongheaded as that is.