A method and apparatus for humidifying air in which the first side of a permselective water transport membrane is contacted with water vapor laden flue gas from a combustion process having a first water vapor partial pressure and a first temperature and at least a portion of the water vapor is condensed, producing condensed water. The condensed water is transported through the membrane to the opposite side of the membrane, which is contacted with an air stream having a second water vapor partial pressure, which second water vapor partial pressure is less than the first water vapor partial pressure, and having a second temperature, which second temperature is less than the first temperature. Upon contact with the air stream, the condensed water evaporates into the air stream, resulting in a humidified air stream.