Passive solar design is the key to sustainable architecture responding to climatic conditions to enhance the comfort and health and resource efficiency. In passive solar building design, windows, walls, and floors are made to collect, store, reflect, and distribute solar energy in the form of heat in the winter and reject solar heat in the summer. This is called passive solar design because, unlike active solar heating systems, it does not involve the use of mechanical and electrical devices. Key features of passive design are location of the building, site orientation, layout of the building, windows design, insulation, thermal mass, shading and ventilation.