I have a Carrier weathermaker gas furnace which is about 12 years old and works well. The exhaust piping goes up (4" pipe) then connects to a 6" pipe and then connects with elbow to an horizontal pipe (about 5' long) than connects upward to chimney. The horizontal pipe is angled slighlty downwards (about 11/2inches over the 5' lenght). Is there a safety issue with the horizontal piping sloping slightly downwards ?

