In existing installations with air valves on waste pipes, it often happens that the condensation water, as a result of temperature differences between the valve and the surrounding air, settles on the valve and, at below-zero temperatures, has frozen and rendered the valve inoperative. An object of the present invention is to rectify this problem by placing a hood over the valve and thereby creating a warmed space between valve and surrounding air. Another object of the invention is to design the insulating hood in such a way that warmed air has continuous access to the warmed space.