What does it mean to weatherize a house?

The idea of weatherization is to control the factors that cause the heating and cooling system from coming on during the winter and summer. Typical energy saving weatherization modifications include insulating walls, ceilings, and floors; sealing the air leaks throughout the home; maximizing window and door efficiency; and tuning or upgrading the heating/cooling system.
Weatherizing also refers to a systematic process of assessing the home’s thermal condition and tightness and its heating/cooling system to determine the most cost effective energy saving modifications. To ensure that the most energy efficient and cost efficient weatherization strategies and materials are applied to the house, the first step should be a comprehensive assessment of the structure.