My gas hot water heater's flue/vent is very hot to the touch. Is that normal? How hot should it get?
As you just noted gas exhaust flues get "pretty hot". Which is the reason they should not be in contact with combustible material. Also they need to be 'double walled' if they are passing through an enclosed surface. Also be sure the vents terminate to the outside, but not in close proximity to any windows or return air registers.