The bypass valves are there to guarantee flow, we are specializing in boiler change outs and sometimes the existing plumbing will not allow the flow we want to see on them, by installing the bypass we have the flow we need and the customer doesn't have to change his system.
Yes I started using it as a flexible connector because if the frost pushes the pad up and the pipe is below the frost lines, it can pull the fittings off the pipe, automotive heater hose seems to be the perfect inexpensive fix.
Heat from the doors, I'm not sure about that because typically when I get called in to service one of the other units, it isn't running. The dry stainless curtain inside the G series definitely makes for a much hotter fire inside the primary chamber as opposed to a completely wet firebox, perhaps the extra heat generated is what you are seeing, we all basically use the same insolation in the doors.