Extraction mode rangehoods 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 rangehoods need ducting and a wall or roof vent. At the same time, a flow of fresh air must be provided, for instance through an open window. Extraction rangehoods are particularly recommended above gas cooktops 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 rangehoods remove most efficiently. At the same time gas cooktops are provided with an adequate supply of fresh air for combustion.