Assume there are two systems with the same mass and specific heat. System A has an average temperature of 500 kelvins and system B has an average temperature of 400 kelvins. If thirty seconds after the systems are put in contact they both reach 450 K, then the average rate of heat flow is:
50 J/30 s, or rather 1.6 W.
(note: specific heat and masses = 1)