Passive ventilation
In this system the process just works without incorporating any design in the building or fitting a mechanical ventilation system. You keep your windows open to allow ventilation. However in this context you should remember the two opposites windows should be kept open on the same floor or one in the top and another in the bottom floor almost facing each other to allow the air move freely between the two.
Exhaust-only mechanical ventilation
This is a low cost ventilation system that uses exhaust fans that are fitted in bathrooms, kitchens or in the utility rooms. These fans run continuously or intermittently to pull out stale air and moisture that have generated inside. This cause pressure difference and allow the fresh air outside to gush inside the house through leakage sites or through strategically placed inlets. A notable disadvantage of this system is that radon and other soil gases get in that we don’t want in houses.
Supply-only mechanical ventilation
In this type on ventilation fans are used to pull in fresh air from outside to a specific area and then it is distributed throughout the house with a ductwork. The stale air inside the house escapes through the cracks and air-leakage sites in the house. This kind of ventilation will prevent radon and other contaminates from entering the house. However it can force moisture-laden air into wall and ceiling cavities where condensation and moisture problems can occur.
Balanced ventilation
These have two separate fans. One of these is responsible for driving fresh air from outside into the rooms. The other propels stale air outside the house. The system can control where the fresh air comes from, where that fresh air is delivered, and from where exhaust air is drawn. These systems can both be ducted as well as point-source. If you have ducted system, then it can be effectively used to ventilate mostly occupied quarters like living rooms and bed rooms etc.