Insulation works to make your home warmer in the winter and cooler in summer. Air is a poor conductor of heat, so the tiny pockets of air trapped in insulation minimize the amount of heat which can pass between the inside and outside of your house. This means that in winter, the heat stays inside the home and in the summer it stays outside! The more heat flow resistance your insulation provides, the lower your heating and cooling costs. Actual dollar savings is dependent on existing insulation levels and how much/if you add to them.
Heat flows naturally from a warmer to a cooler space. In the winter, this heat flow moves directly from all heated living spaces to adjacent unheated attics, garages, and basements, or to the outdoors; or indirectly through interior ceilings, walls, and floors — wherever there is a difference in temperature. During the cooling season, heat flows from outdoors to the house interior.
To maintain comfort, the heat lost in winter must be replaced by your heating system and the heat gained in summer must be removed by your air conditioner. Insulating ceilings, walls, and floors decreases this heat flow by providing an effective resistance to the flow of heat.