Furnace efficiency standards are set by the United States Department of Energy, in conjunction with heating, ventilation and air conditioning manufacturers, utility companies, and other interested parties. Federal laws require a minimum level of efficiency for furnaces, which is measured in percentages of the energy input. The National Appliance Energy Conservation Act recently raised the minimum efficiency requirements for furnaces from sixty-five percent to between seventy-eight and eighty percent. The two percentage point difference depends on whether the furnace is located inside the house or outside, such as in the garage. For every unit of energy that is input, there is a certain amount that is output in the form of heat - as in the case of the furnace. For example, if your furnace has an efficiecy rating of eighty, that means that it will output eighty percent of the energy it takes in. Most major appliances, including furnaces, have an Energy Guide label on them that will tell the consumer how that appliance compares with others in regard to efficiency levels. The label gives consumers an estimate of operating costs for a particular furnace in terms of efficiency standards. For more detailed information on furnace efficiency standards, contact a local heating service professional.