Help with the venting on my water heater

[Tollerplumbing]

I bought a 6 year old house with a State Select PR650XCVIT with a 2" vent, and have a few questions about the installation.

1) It say the termination must be a 2" T or a 3" 45 elbow. Mine comes out the wall, has a 45 elbow and a foot of 2" pipe. So it is not right, but it is hard to see why it matters. Does it?
2) It says to be a minimum of 3' from an inside corner. Mine is 4". Why does that matter?
3) I have 1' of 3" pipe, a 3" 90, a 3-2" reducer, 1 2" 90 elbow, 4 2" 45 elbows, and 20' of pipe. The maximum pipe is 35', each 2" 45 counts as 2.5', each 2" 90 counts as 5' and a 90 counts as 2.5'. So I figure it is 2.5' too long. 20+(7*2.5)
It seems to come out pretty vigorously; is it likely to be a problem?
4) Can I reduce the effective length by increasing some of the pipe from 3" to 2"? I can move the 3" to 2" reducer about 8' further down, and change a 90 and a 45 from 2" to 3". I can't change much more because it isn't very accessible.
5) On the outside there is a 2" 45 and 2' of pipe. It would be easy to put a 2-3" reducer there and change the pipe and the elbow to 3". Is that okay?
6) If #4 and/or #5 are okay, can I extend the outside pipe to get it beyond the inside corner? It says the termination must be as close to the house as possible, but can I make it longer if I insulate it?

[jadnashua]

The fan and burner of the WH are designed to provide a certain airflow. Too much restriction, and it can't move as much air which could affect the heat transfer and safety of the exhaust. PVC can only get so hot before it has structural problems...slow the airflow, and things get hotter. It may also affect the fuel/air mixture at the WH. Exhausting into a corner would also prevent the diffusion of the heat, moisture, and CO that will be in the exhaust. The manufacturer knows its product. I'm sure there's some margin for error, but you've exceeded it, maybe more than a little. I doubt anyone here in good conscience will suggest making it worse by extending your installation. If the install was inspected, one of the criteria is that it be installed per the manufacturer's instructions, plus any local and national codes. It should never have passed inspection.

[Tollerplumbing]

I understand, but that is the point of my question.
I want to get it out of the corner by extending it.
I want to reduce the restriction by changing part to 3".
Telling me it is wrong now isn't helpful; I say that in my post.

[jadnashua]

Going from 2-3-2-3" isn't going to really help - it needs to be larger (nearly) from the beginning. Step back, look at the installation instructions, find a path that will meet the installation instructions WRT max length restrictions. If you can make the entire run 3", that allows it to be longer. Whether that's then within the allowances, the installation manual will dictate. Personally, I wouldn't want a lot of pvc sticking outside in the UV, and, it would cool off the exhaust and potentially cause drainage and maybe freezeup issues. When the installers put my MODCON boiler in, they didn't follow the instructions, it ended up causing the intake/exhaust ports to ice over in a cold spell, shutting the boiler down. After confirming the incorrect install with the manufacturer, I got the installer to rework things at their cost. This is not likely an option with your install based on the time past. Do you know if it was permitted and inspected?