Using energy costs money, and can contribute to pollution. Energy auditors and weatherization workers help customers use less energy, lowering their bills and reducing their impact on the environment. Energy auditors often begin by inspecting homes or commercial buildings to measure heat, cooling, electrical, and gas usage. They use thermal infrared cameras to find energy leaks, and blower-door tests to measure how airtight a structure is. The next step is often to meet with building managers or homeowners to determine how to improve energy efficiency and reduce costs. This requires extensive knowledge of efficient practices, and excellent communication skills. Weatherization technicians improve the efficiency of heating and cooling system ductwork. They repair windows and insulate attics, basements, walls, and other areas. They also prepare bids and contracts for weatherization work. Physical fitness is important for these careers, since energy auditors and weatherization technicians spend much of the day on their feet. They may find themselves anywhere from rooftops to tight crawl spaces when looking for the weaknesses in a building's insulation. Positions are typically available in utility companies, or construction and engineering firms. Many experienced energy auditors choose self-employment to work on their own schedule. Some states require energy auditors to become certified; many auditors learn through up to three years of on-the-job training. Most weatherization technicians need a high school diploma or equivalent.