It your home has already been fitted with an extractor fan, and it has proved to be less than satisfactory, the chances are that it has been sited in the wrong place.
The most common sign of that is poor ventilation – the result of the short circuiting of air movements between the fan and the air inlet. The extractor fan should be sited as far away from and, if possible, opposite the main source of air replacement.
In a kitchen, fans should always be fitted as high up as possible on a wall or window, but it is advisable not to install one immediately above a cooker or grill where temperatures are likely to exceed 40°C. So, the best place for it to be located would be on the wall or window adjacent to the cooker and opposite the door or main air inlet.