Nail said:We know the wall causes [Fire] damage to creatures that pass through it, or come within a certain distance of one side of the Wall. So it's definitely hot.
That's not the point I was trying to make. The point: Deciding if an arrow takes [Fire] damage does not depend on our Real World knowledge of fire. In fact, a real world fire would do few of the things the Wall of Fire does. What we should base our decisions on is rules text....the rest is just idle (and demonstratively wrong) speculation.
Yes. And the rules text states that non-instantaneous magical fire can cause equipment to catch on fire.
Whether that actually damages an arrow when it goes through the 20 feet of heat and the wall of fire is dependent on how literal or liberal one wants to be with various object and fire/heat rules.