For better energy savings you can have a Low E coating fitted into you double-glazed unit. This is a microscopically thin coating which is put onto the inside face of the inner pane of glass meaning it is on the inside of your double glazed unit.

It works by reflecting longer wavelength heat from your heating system back into your home, whilst still allowing short wavelength solar energy in. These short wavelengths are re-radiated by internal building surfaces as longer wavelengths, which are then reflected by the low E coating back into the room.

Low E coating looks like ordinary clear glass as the coating is almost invisible and with a U value 1.8, why would you not want to have it in your home.