Efficiency is defined as the annual heat output of the furnace divided by the annual energy it consumes. This ratio is called the Average Fuel Utilization Efficiency (AFUE). In 2007 the Department ...

Go with the four-wheel drive version of the same truck, and the EPA estimate drops to 20 mpg combined (19 city/22 highway), increasing the annual fuel cost to $2,300. The fuel-economy difference ...