http://www.homeinspectioncarolina.com Do you have ice around your furnace exhaust? Here is why. You probably have a high efficiency furnace. The secondary heat exchanger is made up of small tubes that receive the exhaust gases once they have gone through the primary heat exchanger. Here, more heat is extracted from the exhaust gases, and as a result, the gases are cooled to the point that they condense into water and carbon dioxide. The water vapor freezes when it hits outside cold temperatures. If its not blocking the exhaust its not usually a problem. http://www.askthachrlotteinspector.com