How do I vent a gas hot water heater?

I am looking to find out what materials I will need. It is going through and exterior wall, not a chimney. If you could also supply a diagram, that would be very helpful.

This is one of those things that if you have to ask you probably shouldn't attempt it. There are several safety items like venting sizeing , length, and number of turns. each would affect the other. ther is also making sure you have a neutral or positive pressure situation. To much to consiter for a forum such as this.

If this is not a power vented water heater then it is not legal to just vent through the wall.The vent termination should be above the roof.This can be done on the outside wall of the house with B-vent pipe.There are too many code requirements to list here.These requirements are covered in the National Fire Protection Agency's publication #54 {usually referred to as NFPA 54}

I would use insulated stove pipe (double wall). You will probably use measured lenghts of pipe,2 elbows,and a weather cap for outside. I think It's wise to insulate pipe from touching any flammable surface even though the pipe is double and insulated. There are other factors and if you never have done this before and obviously you haven't , I would enlist the help of an experienced professional. Improper installations can cause fires.

Double pipe is what you need, only do this yourself if it is a simple through the wall and out installation. If it has bends, is longer than a couple of feet, or passes near to combustibles like insulation , then you need professional help. This installation doe wrong is a fire that will happen, if not tomorrow, then in five or ten years. You need to have some engineering wrapped around this project!