Power vent
A power-vent water heater uses a fan to push exhaust through plastic pipe out a sidewall, instead of relying on a natural-draft chimney. It frees placement from the chimney but needs an electrical outlet and adds fan noise.
Power venting uses room air for combustion and a blower to exhaust it. That flexibility makes it the common choice when replacing a unit far from a usable chimney, or in tight modern homes where natural draft is unreliable.
When replacing a water heater, matching the existing vent type is usually the cheapest path — switching vent categories means new penetrations, pipe runs, and sometimes combustion-air provisions.