Question

Why ventilators are located near the roof?

Answer 1

It is done to remove the harmful impure air and to replace it by the cool fresh air. The air we breath out is warm and so it is lighter. It rises upwards and can go out through the ventilator provided near the roof. The cold fresh air from outside enters the room through the doors and windows. Thus, the convection current is set up in the air.

Hope it helped

Answer 2

The hot air being lighter in weight tends to rise above and escape from the ventilators at the top. This allows the cool air to come in the room to take its place.