This new unit uses PVC venting and has a second heat exchanger to recover heat from the vent stack. Ninety-five percent efficiency (LP) aside, I wonder if the savings on Cat III vent will offset the higher cost of the unit? I haven't seen prices yet. Whatever the case, this is an intriguing tankless unit:

http://takagi.com/index.php?product_id=85&page_id=2