When choosing a new furnace, find out its “AFUE” – annual fuel utilization efficiency. It’s a term for describing a furnace’s seasonal energy performance. Why should you care about the AFUE? Given the rise in energy prices and uncertainty about future energy sources, your priority should be lower energy bills. High-efficiency appliances use less energy, lowering your costs. By federal standards, new furnaces must have an AFUE rating of 78 percent.