Many of us use space heaters to stay warm on cool days, especially if we're chilly at our offices or in a poorly heated room of the house for extended periods of time. But we're also under the misconception that space heaters are energy-efficient alternatives to our overall heating system. The reality is, they use more energy than, say, a gas furnace, which only uses 43 percent of the energy of a space heater, according to the Department of Energy. To keep you feet and legs warm at your desk, skip the space heater and think heating pad. Rest it on the floor and put your feet on top. It'll keep your feet warm, and the heat will rise to the air above it, all while being more energy-efficient.