I know it is always being touted as equivalent to double glazing, but low-E on its own is really no substitute for plain double glazing. Reason is low-E works on radiant heat, and double-glazing works on conducted heat. Around 90% of all heat loss from the home is lost through conduction. Low-E’s biggest advantage is in reducing the solar heat gain coming into the home which is entirely from solar radiation.
But better by far in stopping radiant heat is to shade the window. In short, low -E has value where it stops radiant heat from the sun entering your home when that heat would require cooling, and in Australia, that would be to the North and West facing windows.
Important Reminder! Double glazed windows–Uw values
! When you compare window energy performance in WERS or in your energy report, check that the windows that you are comparing have the same glazing configuration, (I prefer to check the clear glass option (4/12/4), this way you are checking the true energy performance of the window, notsimply the glass). Also make sure that it’s the same style of window e.g. awning with awning and not awning with fixed (fixed windows perform better than opening windows because they have less aluminium)