Heat flows naturally from a warmer to a cooler space. In winter, heat flow moves directly from 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.

Even though you need some moisture in the air you breathe, too much moisture in your home can cause problems. When moist air comes in contact with a cold surface, some of the moisture may leave the air and become liquid, or condense. If moisture condenses inside a wall, or in your attic, you will not be able to see the water, but it can cause a number of problems.