Indirect evaporative cooler construction

A counter flow indirect evaporative heat exchanger wherein vertically adjacent counter flow wet and dry passages are, when in situ, horizontal or near to horizontal and the wet passages being wetted by wetting means and dry passages constructed to prevent being wetted by wetting means by the flow of air from the dry passages toward the wetting means, the wetting means sequentially applying which applies water elongately to the wet passages across the height of the heat exchanger,

• wherein the wetting means includes a water delivery device which travels generally vertically of the heat exchanger delivering water directly into a small plurality of the total number of passages at a time along an air delivery face of the heat exchanger.