A Passive House takes advantage of the largest free source of energy on the planet, the sun. By orienting the main windows in the building to face north, there is a significant amount of energy gain within the space. Along with the heat given off from the occupants and appliances, this is often all that is required to keep the home comfortable year round. A ventilation system is still required to provide fresh air throughout the home. The ventilation system transfers fresh air into the home from the exterior while a heat exchanger extracts the wasted heat from the air that is exhausted to the exterior. The excess heat is then recycled within the heat exchanger unit to heat the fresh air coming into the home. Cooling a Passive House Building relies on its super insulated shell and the airtight building envelope which prevent the sun from heating up the space. Designing the roof to have large overhangs, operable shutters on the windows and even light cladding colours are all basic strategies that when coupled with effective natural ventilation ensure that a Passive House Building is cool throughout the hot summer months.