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The double glazing part of the window is the glass, or sealed unit, this comprises of two panels of glass, i.e. double glazing or double glazed.

 Replacement windows glass panes are kept apart by a spacer bar which contains hundreds of tiny silica balls. These same balls can be found in the little bags you find in the packages when you buy electrical goods to keep them dry and free from moisture. It is these balls which soak up any moisture which exists in the air gap between the two panes of glass.

Turning to the sealed unit itself, the insulating effect of double glazing can be affected by a number of factors.

  • Double glazing insulation is affected by cavity width of the sealed unit.
  • The use of argon instead of air in between the panes.
  • Utilising a low emissivity coating that reflects heat back into the room.

Our replacement windows now offer a greatly improved insulation compared to traditional single glazing openings. In addition to their better insulation, replacement windows are also draught-proof, therefore reducing the amount of heat that can escape, so you can cut down on your heating and save on fuel bills without sacrificing comfort.

The insulation of replacement windows is measured in U values (the measurement of heat transfer through the window it's self). The following table illustrates some typical sealed unit U values using various combinations of cavity widths, air or argon and Pilkington K Glass, which has a low emissivity coating.

Pilkington-k double glazing Cavity width: 10mm 16mm 20mm
Optifloat/air/Optifloat 2.9 2.8 2.7
Optifloat/argon/Optifloat 2.7 2.6 2.6
Optifloat/air/Pilkington K 1.9 1.8 1.7
Optifloat/argon/Pilkington-K S Soft coat 1.3 1.2 1.1
Overall width of unit in millimetres 18.0 24.0 28.0

note. Optifloat is the name given by pilkingtons to standard clear glass.

Typical Planitherm and K-Glass characteristics



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