Kitchen gas accident fan can not be put on the roof. Put on the roof, the disadvantage is that the noise heard full true, will affect the indoor people's conversation, if you do the muffler treatment, will occupy a large area of the kitchen, and even affect the operation in front of the stove. Advantage is that the blower outlet is close to the stove, need to connect the pipe is short, the wind stove hand rent pressure loss is small, must buy the blower pressure is small, the blower will be cheaper. Placed outside the room, the advantage is that the noise will not be directly in the ear, if there are conditions, the blower can be equipped with a sound canceling box, the noise of the entire environment are small.