I am not sure if it is appropriate in this forum but I will give it a try.
I just corrected a very bad(dangerous) situation in a home in Phily. They had fireplace smoke come down the hot water exhaust, in addition to that, the down draft in the hot water heater in the basement was so bad that the exhaust gases would not make it through the chimney, instead the would disperse in the finished basement.
We installed a fresh air vent and installed a Chimney Cap Art chimney cap. (Not like anything you've ever seen. The home owner is as happy as a lark and the downdraft in the basement has COMPLETELY stopped.
Send me an Email, I will return it with pictures.
Check out www.chimneycapart.com