In a coal-fired power plant wherein pulverized coal is entrained with a temperature-controlled hot air stream to feed a combustor where combustion occurs, such hot air stream being created by tempering relatively hotter air with relatively colder air by mixing streams of such relatively hotter and colder air, the improvement which comprises an air mixer comprising a first inlet at which the stream of relatively hotter air enters the air mixer, a second inlet at which the stream of relatively colder air enters the air mixer, and an outlet from which the relatively hotter and colder air streams exit the air mixer to form the hot air stream, said air mixer comprising a series of parallel rectangular walls that are arranged in side-by-side, spaced apart relationship to each other to form a series of rectangular spaces each lying between consecutive ones of said walls and having a perimeter composed of four sides, means closing alternate ones of said spaces along the same first one of said four sides while leaving the remaining ones of said spaces open along said first of said four sides, said remaining ones of said spaces forming a first group of said spaces and said alternate ones of said spaces forming a second group of said spaces, means closing the spaces of said first group of said spaces along the same second one of said four sides while leaving the spaces of said second group of said spaces open along said second of said four sides, and means closing the spaces of both of said groups of said spaces along the same third one of said four sides, means for communicating said relatively hotter air stream to said first of said four sides of said spaces to cause said first inlet to be said first side of said spaces of said first group of said spaces, means for communicating said relatively colder air stream to said second of said four sides of said spaces to cause said second inlet to be said second side of said spaces of said second group of said spaces, means leaving the spaces of both of said groups of said spaces open along the same fourth one of said four sides to cause said outlet to be said fourth side of said spaces of both of said groups of said spaces, and air turning vanes in at least one of said groups of said spaces for turning a portion of the particular one of the relatively hotter and colder air streams passing through it.