Black Knight Secondary Glazing
Black Knight Secondary Glazing

Thermal test results - secondary glazing

A thermal window insulation test carried out on the aluminium secondary glazing unit by the Interver glass testing centre * is summarised as follows:

  • existing primary window - timber, 4mm glass, putty glazed
  • cavity - unsealed 85mm
  • secondary window - aluminium hardwood subframe, channel glazed, Pilkington K low emissivity glass
Thermal insulation for windows Secondary window thermal insulation testing

Thermal test results summary


  • the combined secondary glazing thermal insulation U value for this configuration was 1.868 W/m²K
  • using 6mm Pilkington ‘K’ low emissivity glass gives 1.5 W/m²K
  • this will be equivalent to a WER rating scale of B or C 
  • using double glazed low emissivity glass will give a window insulation rating scale equivalent of A

* The thermal test results certification are available on request