Casement windows are actually more energy-efficient than any other operable window type on the market, according to the U.S. Department of Energy. Because their movable sashes press so tightly against the frame and weatherstripping, there is significantly less air leakage when closed and latched (great for the colder months). When open, airflow is maximized because the sashes can be rotated completely away from the window opening (a huge plus during warmer months). And just like other energy-efficient windows, they can be purchased in double or triple glazed models with low-e glass for superior insulative properties.