Drought from timber windows

[akkers]

I have timber double-glazed windows (installed around 1993). In one room there is expansive drough coming from the windows. I sealed the windows with silicon to the core and cannot see any gaps or anything anymore. But there is still draught coming from around the windows; I cannot work out where its coming from.
I have tried the smoke test but I am none the wiser.

 

[Wayners]

Hire or buy a thermal imaging camera

 

[Harry Bloomfield]

I have timber double-glazed windows (installed around 1993). In one room there is expansive drough coming from the windows. I sealed the windows with silicon to the core and cannot see any gaps or anything anymore. But there is still draught coming from around the windows; I cannot work out where its coming from.
I have tried the smoke test but I am none the wiser.

Are you sure it's a draft through leakage, rather than air falling, as it cools on the glass? Windy weather, best shows up actual leakage.