Water vapor contributes a maximum of 1°C/day to the middle atmospheric thermal infrared (IR) cooling. The accuracy and efficiency of two IR parameterizations are examined in this study. One is the correlated-k distribution method, and the other is the table look-up using precomputed transmission functions. Both methods can accurately compute the cooling rate from the earth's surface to 0.01 mb with an error of only a few percent. The method of table look-up is much faster than the correlated-k distribution method for computing the water vapor cooling profile involving both the middle and lower atmospheres.