Extraction mode cooker hoods draw the cooking vapours in and remove grease particles with the help of the grease filter. The filtered air is then transported out of the kitchen via vent ducting. Along with the filtered air, any excess moisture and odours are removed from the kitchen. In order to channel the extracted air outside, extraction mode cooker hoods need ducting and a wall or roof vent. At the same time, a flow of fresh air must be provided, for example, through an open window. Extraction cooker hoods are particularly recommended above gas hobs as well as for frequent deep-fat frying, grilling or use of the wok. This type of cooking generates a lot of heat, grease and steam which these cooker hoods remove most efficiently. At the same time gas hobs are provided with an adequate supply of fresh air for combustion.