Seven Summer Blunders that Bump the Bill From Duke Energy Newsletter Let the sun shine in? This is great in the winter, bad in the summer! During peak cooling hours, solar heat (a fancy name for sunshine) gains can account for one-third of the load on an air conditioner. When home, close the drapes on the sunny side of the house, or close all window coverings if leaving for the day. Be cool, but not too cool. For each degree cooled below 78, cooling bills can rise by as much as 10%. On the other hand, raising the thermostat from 73 to 76 degrees could save 30% on air conditioning costs. Control the humidity. While it is tempting to give the air conditioner a rest on cool nights, watch the weather forecast. If tomorrow is going to be hot again, keep the air conditioning on and the home closed through the night to keep the humidity out of the house. Humidity is a significant load on an air conditioner. Ductwork. If air conditioning ducts are visible in an attic, more insulation is needed on these ducts. Cool air ducts in a 120 degree attic in the summertime need to be fully buried under 6 inches of insulation. The factory insulation you see on these ducts is usually only about 1 inch thick and not adequate for hot attics. Heat absorbed by exposed attic ducts can add 20 to 40% to your bills. Older Model Air Conditioners. New, high efficiency, 13 SWEER air conditioners will use only half the energy compared to a 15-year-old air conditioner. If an air conditioner is 10 years old or less, maintain it well and keep it. If it is between 10 to 15 years old, minor repairs are okay. If an air conditioner is older than 15 years and needs substantial repairs, its best to replace it with a new, high efficiency system. Super-size me! This is questionable advice for a French-fry order, and very definitely poor advice for a new air conditioner. A properly sized air conditioner is very important for comfort, humidity control and energy bills. When buying a new air conditioner, it should be properly sized, based on a detailed energy analysis of the home. Old refrigerators. Many faithful old refrigerators seem to run forever, and its so easy to find an unused electric outlet in the garage. But an old refrigerator may use twice as much energy as a new energy- efficient refrigerator. Refrain from putting the old one in the hot garage where it is only partially filled and seldom used. This seemingly resourceful action could add $180 per year to an energy bill.