Abstract: An inlet device for the wall of a building for example an animal barn comprises a simple moulded rectangular body through which the air can pass having an open mouth at one end and an inlet surface in a lower downwardly facing surface on the outer side of the wall. A door on a front face of the housing is hinged along a flange on the lower side of the housing as to hang down in the open condition. The door includes a foamed projection which can seal with a recess surrounding the open mouth of the housing. Inside the housing is provided a foamed plate-like shutter which is spring biassed into a closed position against flanges along the sides of the housing. The base of the shutter is freely mounted in a v-shaped area defined at a step above the lower surface of the housing to prevent freezing.