The draft diverter is a steel cap that sits on top of a standard Atmospheric gas water heater. The draft diverter is designed to capture all of the carbon monoxide from that gas burning appliance. The flue pipe or vent that terminates through the roof is directly attached to the draft diverter.
It’s very important that the draft diverter is attached to the water heater properly. If the draft diverter is not fitted properly carbon monoxide can seep into the home. It’s also recommended that you do not connect a 90 directly to the draft diverter.