Ventilated dry type transformers are designed for application indoors in dry locations. It will operate successfully where the humidity may be high, but under this condition it may be necessary to take precautions to keep them dry if they are shut down for appreciable periods. Adequate ventilation is essential for the proper cooling of transformers. When transformers are installed in vaults or other restricted spaces, sufficient ventilation should be provided to hold the air temperature within established limits when measured near the transformer inlets. This usually will require a minimum of 100 ft3 of air/min/kW of transformer loss. The area of ventilating openings required depends on the height of vault, the location of openings and the maximum loads to be carried by the transformers. This ventilated dry type transformers should be installed in locations free from unusual dust-producing mediums or chemical flames.