Direct vent
A direct-vent water heater draws combustion air from outdoors and exhausts outdoors through a sealed two-pipe or concentric arrangement — no indoor air is used, eliminating backdraft risk and depressurization problems.
Because the combustion loop is sealed from the living space, direct venting is the safest configuration for tight houses and for mechanical rooms near return-air ducts. "Power direct vent" adds a fan to the same sealed arrangement for longer vent runs.
The certified record lists each unit's vent type and vent sizes; both matter for a like-for-like replacement quote.