The QUANTAPANEL 604-DH Architectural Low-e Storm Window installs on the interior of an existing double hung window. Installation of the QUANTAPANEL 600 Series is through pre-drilled holes via screws that attach to the window jamb perpendicular to the plane of the window. A compressible seal on the perimeter of the frame ensures a tight seal, and allows for slight out-of-square conditions in the window opening. This 3-track system has a removable upper sash, an inner sash that opens vertically to adjustable heights to allow for fresh air ventilation, and removable screen in the innermost track. This product can be specified with a full window screen, and is often used in this configuration for multi-season rooms that serve as screened porches during the summer months. The patented QUANTAPANEL 600 Series provides for air infiltration reduction comparable to a prime window, which is necessary for optimum performance of an interior secondary sash system. This product is ENERGY STAR certified. The QUANTAPANEL 604-DH Architectural Low-e Storm Window are available in standard or custom colors (185 colors to choose from)!