Exhaust gases are vented outdoors through a separate vent duct or through a separate chamber of the same pipe this requires a double wall vent duct.
Venting a gas water heater through wall.
The only other option is an electric water heater which requires no vent.
Instead both systems typically expel exhaust through a pipe that runs outside through an exterior wall.
Direct vent water boiler.
Yes you can vent a gas fired water heater out of the wall if it is either a power vent unit.
This water heater is found in different homes.
All solid liquid or gas fueled water heater whether they are tank type or tankless must vent through the roof unless they are direct vent.
Direct vent water heaters with a direct vent system air for combustion is drawn from a vent pipe that runs through an exterior wall or the roof.
Venting a hot water heater through the wall atmospheric water heater.
The difference is that a power vent water heater pulls in combustion air from the space.
The atmospheric water heater is very common.