I haven't quite made it to the attic with it yet, as it stands now it comes out of the cubby it's in and runs about 6 feet away along the ceiling. Far enough away from the unit so as not to mix the cold exhaust into the intake. I don't have any solid numbers about the effect, but it has got to be slightly better since it gets the hottest air in the garage all the time and doesn't mix with the cold. One day I'll finish getting it up to the attic, that project is just a little further down my list.Did the attic duct help?
I'd think that pulling hot air into the unit would be beneficial.
I have a 1st gen AO Smith hybrid water heater, going on 11 years old now. I'm still quite happy with it. As I mentioned, it cools my garage, and this is really nice when living in South FL. But getting into the truck when the garage is cool really helps, as both my wife and I are heat intolerant now.