You guys nailed it. I hooked up my leaf blower and produced no results. So then I ran my dryer vent brush up the vent. About 20 feet up the brushed stopped. I pulled the brush out and a huge nest came out with it. I ran the brush up a few more times. When it popped out the top of the chimney, I knew I got it all.
What gets me is the company that wanted to replace his 6 year old water heater because of a vent problem. He finally got them to admit that it was probably just a bird nest. Supposedly they're a top rated company on Angies List, too.
Thanks a lot for the help.