Can I add another connection to my chimney?

A lot of the new hot water tanks can just be vented with a pipe(plastic) to the outside of the house. Check and see........also Yes, you can put a "Y" in the line and vent into an existing thimble if needed. Grab some directions before buying and you may fine one that is easier than you think. Good luck........hope this helps and have a merry xmas. By the way, does the chimney have a flue liner in it?? That is always my concern? It would be a lot safer if it does.