Faganel Builders uses power vented water heaters in all our homes.  The primary purpose is safety, by eliminating any chance of dangerous backdrafting that can occur in tightly-built homes.  Most conventional water heaters have a "natural-draft" type of vent, where the hot gases rise through an open draft diverter and into metal pipes, which eventually lead to the outdoors.

In contrast, a power-vented type uses a fan to blow the exhaust gases out.  Since this method doesn't rely on the natual buoyancy of hot air, the vent pipes don't have to go upward.

Further, the fan dilutes the exhaust with cooler air so the vents are run with PVC pipe.  Power venting is an especially good solution for more energy efficient, tightly built Faganel Builers Millennium III® Green homes, where a natural draft is difficult to establish.