Although kitchen chimneys differ from model to model, they operate on similar principles. A chimney is used in conjunction with a stovetop to vent steam, grease and food odours to the outside of the home or through filters back into the kitchen. The air is circulated through the chimney by a fan motor which is energized by voltage sent to the motor when the fan switch is actuated. Some models will have one or more motor speeds to achieve optimal venting. A standard grease filter is used when the steam is being vented to the outside of the home. A charcoal filter is required if the steam is being recirculated back into the kitchen.