It’s pretty easy to tell how efficient a propane furnace is. Just check the Annual Fuel Utilization Efficiency (AFUE), right? Not so fast, writes Allison Bailes in Energy Vanguard. “Unlike air conditioners and heat pumps, furnaces use two sources of energy,” he says. “The fuel that it burns is the obvious one. (It’s usually natural gas or propane.) The other is the electricity that runs the blower. And that’s the key to finding a high-efficiency furnace that truly operates at high efficiency.” Read on to see how choosing a furnace with an efficient motor can save a homeowner thousands of dollars over the life of the unit.