Home inspectors, you got to love them,
either way their reports can be very entertaining.
Check out this picture of this guys report.
The section under Plumbing is what I am speaking to.
The flue from the fifty gallon water tank was 3" for about a foot, then it converted to 4". The inspector demanded the entire size be 3" like that would be better.
The original flue pipe was touching the hot water outlet pipe, he writes this up as a danger. His reasoning is quite entertaining like this scenario could ever really happen.
He also did not like the line on the relief valve, it is the type sold at most plumbing supplies, it starts off with a metal nipple and converts to plastic pipe.