When performed by a central piece of equipment called a "forced air system," the necessary air to heat, cool, or ventilate your home has to travel through ducts that have been laid throughout the interior walls and floors and ceilings of the building.
Ventilation basically means to change or replace the air in any room or home so as to improve the indoor air quality. It is a catchall term that can refer to controlling the temperature, remove any excess moisture, odors, smoke, heat, dust, airborne bacteria, or carbon dioxide. It can also freshen the air by replenishing the oxygen supply. Ventilation is the antidote to stale, stuffy, stagnant interior air. But it can also be used to remove unpleasant smells and excessive moisture.