Air flow is the primary component of ventilation and air flow can be achieved by a number of strategies. These strategies are as follows: The first one is convection and this occurs when the heated air rises to the top naturally, creating a current of warmer air that displaces cooler air. The second strategy is diffusion and it occurs when hot or cold air molecules move about. The third strategy is natural ventilation which happens through windows, doors, cracks and crevices even without human intervention. Lastly, mechanical ventilation involves the transfer of heat into the surrounding by using fans or pipes.