The Effect of gap size to counter current flow limitation (CCFL) in vertical rectangular channel was studied in this paper. Experiment was conducted by using two vertical plate with 1 mm, 2 mm, and 3 mm narrow gap. The initial temperature of plate was decided at 600°C. Flow rate and temperature of cooling water were controlled about 0.09 L/s and 90°C respectively. Non-dimensional superficial velocity for water is 0.05-0.09 and non-dimensional superficial velocity for vapor is 3.20-3.2. The result shows that the existence of CCFL in the vertical rectangular narrow channels. A new correlation for CCFL base on Wallis has been proposed.