Heritage double glazed sealed units with super spacer that have low sightline and thickness which is ideal for replacement of single panes of glass in existing timber windows to double glazing resulting in better thermal and acoustic insulation. This method avoids the need of complete window replacement resulting in cost effective window upgrade and quicker turnaround. The spacer between the 2 panes of glass is 4mm thick heritage space and is available in 2 colours, black and white. The glass that can be used is either 2mm, 3mm, 4mm or thicker of different combinations. 4mm glass can also be energy efficient glass to achieve better U values and better thermal insulation.