Increase insulation. Do you know what's in your attic? More than 30 percent of homes in the United States are not insulated, according to Rick Heede, a consultant with the Rocky Mountain Institute, a nonprofit organization that fosters efficient resource use. Millions more are underinsulated. According to EERC, some local building codes require lower R-values than the Department of Energy's recommendations. R-values measure resistance to the flow of heat through a given thickness of a material: the higher the R-value, the better the insulator. If you find your home's insulation levels are less than the recommended levels for your area, you need to make this your first improvement project. [check] Uninsulated recessed ceiling lights are as bad as holes in your ceilings. These lights keep their bulbs cool by letting air flow through holes in the top of the fixture. To correct this, you can add insulation, but remember to allow 3 inches of airspace between the light and the insulation to allow some circulation. A better option is to buy replacement lamps that are marked "LC" This indicates the lamps are approved for direct contact with insulation. [check] Insulation not only keeps heat inside in winter, it keeps heat outside in summer. If you live in a warmer climate, consider installing a radiant barrier. Thin reflective plastic sheeting installed in the attic under the roof can reduce heat flow by 50 percent, thus reducing air-conditioning costs. [check] Ventilation plays a large role in controlling moisture and reducing summer cooling bills. As you're insulating, sure you have adequate attic ventilation (about 1 square foot per 150 square feet of attic space). Also make sure there's good airflow, from the soffit all the way to the ridge. [check] Turn down thermostat. Each degree you lower the dial in winter decreases your fuel bill an average of 3 percent. Going from 72 to 68 degrees may not feel like much, but it can save you 12 percent on your energy bill. To save even more, consider a programmable thermostat ($25). For an annual savings of 10 to 20 percent, set the unit to lower the temperature to 60 degrees when you're sleeping or away from home. The thermostat can also save you money in the summer by turning off the air conditioning during the cooler evening hours or when you're not at home. [check] Change furnace filters. If you have a forced-air heating system, replacing your furnace filters monthly can save about 5 percent on your energy bill. Just as important, clean filters keep dust and grit out of the heater and out of the indoor air. Write the date you change filters on the cardboard frame for reference. [check] Fix your fireplace. A crackling wood fire provides a primal pleasure, but that roaring fireplace can exhaust 20,000 cubic feet of heated air per hour, and draw in cold air from the outside, forcing your furnace to work overtime. When the fireplace is not in use and the damper is left open, the same amount of heated air escapes up the chimney as from an open, 48-inch-wide window. For maximum savings, the Rocky Mountain Institute's Heede recommends plugging the flue, but if you can't resist the pleasure of open fires, install a set of glass fireplace doors to prevent large volumes of unheated air from escaping. And always keep the damper door closed when not in use. The spin on fans. Ceiling fans can actually earn their keep. Using about as much electricity as a 100-watt light bulb, a fan's circulating abilities can lower utility bills by providing both cool and warm air. During the summer, a ceiling fan's breeze can make you feel 5 to 10 degrees cooler. If you bump your thermostat up these 5 to 10 degrees, you can shave 15 percent or more off your electric bill. In winter, switch the fan to reverse, and run it on low to move hot air down from the ceiling. If you have cathedral ceilings, bringing the heat down to ground level can save you as much as 10 percent. .