Water Heaters - Venting Gas Water Heater into a Chimney

I will be installing a new gas water heater in my home and would like to know how to vent it properly in a chimney. Is there an insert or sleave that needs to be installed into the chimney? If so, what is it called and how do i install it? Im a little confused as to what exactly gets inserted into the chimney. I saw thimbles being used, but they look as if they are used to go through the exterior of a wall to vent outside the home. Thanks in advance.

You need to refer to the manufacturer's installation instructions, because it depends on the heater design. Most of today's gas water heaters take more energy out of the exhaust gases than older style heaters. That means that the exhaust gases are cooler, with more moisture. A flue for an older heater may be too big for a new heater. The exhaust can cool too quickly to provide adequate draft. You may have to install a liner in the chimney, which is a flexible flue pipe that runs all the way up the chimney. It has to be sized to your heater.