All transfer of heat energy occurs as the result of convection, conduction or radiation. Convection occurs when heat energy moves through a duct system and carries heat energy from the furnace to the room being heated. This process also occurs when hot outside air infiltrates the home through leaky window gaskets or door thresholds. While this is of great concern in harsh climates, it accounts for only 3 percent of the typical home s air conditioning load, according to the Florida Solar Energy Center. Windows, doors and other openings in the home s thermal envelope should be as leak-free as practical.
Conduction occurs when heat energy moves from molecule to molecule through a substance.
This only occurs when the conductive substance forms a barrier between hot and cold areas. Conducted heat always flows from hot areas to cold areas. The greater this difference in temperature, the greater the conducted heat flow. Substances that resist this heat flow are said to be good insulators. This insulating ability is measured in R-values.