I just got one of these T-H3-DV.
http://www.takagi.com/index.php?prod...=133&page_id=2 Takagi USA - The tankless water heater pioneers. Experience "Endless Hot Water"[/url]
The Energy Factor of 0.95 is hard to beat and it vents with PVC.
If you shop around you can get it for about $1,000 shipped. Mine even came with free isolation valves for cleaning it.
12 year warranty heat exchanger and 5 year on parts.
This is where I got mine. They still have free isolation valves until end of Dec.
http://www.build.com/takagi-th3dv/s822340
find a coupon code and do even better.