I want to understand something once and for all about warm air and cold air.

Lets say you have 2 rooms next to each other that are complete boxes and a small opening (say a a square foot) in the wall that separates the rooms. One room is 70 degrees and the other is 45 degrees.

All other things being equal (humidity, dew point, etc), how would the air flow "feel" ? If I held a lighted match in the middle of the opening which way would the flame bend?

Toward the colder room?

Seems that when I've encountered this, I always feel the air flowing into the colder area -- bu then I read somewhere recently that wash hogwash.

I'm not an HVAC pro or anything -- just curious. THANKS.