The diagram below illustrates how heat is lost and energy wasted in a house because of air getting into and out of the house.
Overall, heat is mainly lost escapes through the upper areas of the house, while cold air enters from lower areas. As a result, energy is wasted due to air movement.
In the upper areas, warm air escapes through the attic hatch and recessed lights. Heat is also lost through the bathroom and kitchen fan vent. In addition, air leaks out through small gaps around electrical outlets and the plumbing stack vent. These openings make it easier for warm air to rise and escape from the house.
In contrast, cold air enters the house through the crawl space and around the outdoor faucet. As warm air escapes the house, cold air is drawn inside from these lower areas. Therefore, energy is wasted because of continous air leakage.