According to Energy.gov, a high-efficiency furnace works by condensing gas in another heat exchanger, yielding a more efficient system. A furnace with high efficiency also has sealed combustion for better performance, and a system of this quality has a range of 90 to 98.5 percent Annual Fuel Utilization Efficiency (AFUE).
HomeTips.com notes that the AFUE is measured in terms of heat consumption. A high-efficiency furnace with a 96-percent AFUE means that it is transforming air into 96-percent consumable heat. When it comes to comparison between an oil and electric furnace, one notable difference is that the electric option does not contain a flue, but since electricity is more expensive, many choose a fossil fuel-based furnace.
According to Dr. Energy Saver, high-efficiency oil furnaces tend to have sealed combustion systems of the condensing variety. It works by using a plastic tube that carries combustion air to the chamber. A secondary exhaust process, known as the condensing cycle, cools any gases. As a result, no chimney is necessary. A high-performance system typically operates at 96 percent AFUE, Dr. Energy Saver notes. An older furnace can operate at only 75 to 80 percent AFUE. Highly efficient oil furnaces that have a 96-percent AFUE rate decreases heating oil payments each year by hundreds of dollars.