Combustion air intake under wood-framed porch?

[Crashcup]

Just reading through the installation instructions for a wood-burning FP we're considering buying, and the instructions, in the section on Combustion Air Inlet, include this:
"As a precaution the combustion air ducting must be kept away from combustible material because a reverse air flow of hot gases may result while the unit is in certain operations such as burning with the doors open."

The closest place for us to run combustion air inlet is into the basement, along a floor joist space about 5', and out the rim joist, with the termination under our wood-framed porch.

Has anyone heard of this being a real hazard? Reversal of hot gases through the intake, resulting in burning material around the intake?

 

[webby3650]

I've never seen this in the directions for any units I've installed. It doesn't make a lot of sense considering there are no guidelines for clearances to the combustion air pipe. Often times the termination is on vinyl siding..

 

[iamlucky13]

I've seen mention of it before, but not significant clarification.

Does the stove you're installing require an outdoor air kit like this, or can you just let it draw room air and install a combustion air vent to let outside air into the room when needed.