Without knowing the water heater type vent type location and type of termination no one can give you a more definitive response.
Can you vent a hot water heater out the wall.
Two specialized types of water heaters direct vent and mechanical vent also called power vent are exempted from this code requirement.
Installing your tankless water heater for easier venting.
The only other option is an electric water heater which requires no vent.
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.
Yes you can vent a gas fired water heater out of the wall if it is either a power vent unit.
Most tank type gas water heaters are atmospheric vent type and they are required to vent vertically and above the roof of a home.
If the unit is installed on a basement wall the vent pipe can be run up just a few feet and then vented out the side with the use of a 90 degree elbow.
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.
The difference is that a power vent water heater pulls in combustion air from the space.
Photos go a long way.
Exceptions may be made for non combustible walls such as solid masonry.
Single wall vent pipe cannot be used for water heaters located in attics and may not pass through attic spaces crawl spaces or any confined or inaccessible location.
Single wall vent pipe cannot pass through any interior wall.
Instead both systems typically expel exhaust through a pipe that runs outside through an exterior wall.
If your water heater is near an outside wall you can go with a direct vent water heater.
A blower or power vent draws combustion air in to the heater and a power vent pushes exhaust gases out through a separate or dedicated exhaust flue.
They do make two models of power vent units one is called a direct vent power vent as bob harper pointed out it draws its combustion air from outside unlike a standard power vent unit which burns its combustion air from the dwelling.
Water heaters and vents come in multiple forms including induced draft direct venting and conventional draft.
With a direct vent system air for combustion is drawn from a vent pipe that runs through an exterior wall or the roof.
This one vents out the side wall and it is perfectly fine.
Can a standard water heater be side vented.
To make venting easiest install your tankless water heater on an outside wall.