When swapping the glass is the sensible fix, and when it's money spent on a frame that's already finished.
A misted pane is a failed seal, not a dirty window — the sealed unit has let moisture between the panes and no amount of cleaning will clear it. The good news is that the glass can usually be replaced without touching the frame.
The decision that actually affects your spend is whether the frame is worth keeping. This guide sets out how we judge that on survey so you are not sold a whole window you did not need, or a glass swap into a frame that fails next winter.
Sealed units are priced per unit, and these are the variables that move the figure:
Glass replacement fixes the glass. It does not fix a frame that has dropped, hinges that have worn, or a window that was never energy efficient to begin with.
If the frame is sound and the window is reasonably modern, glass-only is almost always the right answer. If several units have failed across the same elevation and the frames are tired, replacing the windows usually costs less over the next decade than repeated glass visits.
Any competent installer should answer all of these without hesitating:
Send us the number of misted panes and rough sizes and we'll come and measure properly before quoting.
No. Drilling and 'defogging' treatments do not restore the seal or the insulating gas fill. The unit needs replacing.
Usually not. If the frame and hardware are sound, we replace the sealed unit only.
Often yes, if the window is still within its original guarantee period and you can evidence the original installation. We'll tell you if we think you should claim rather than pay.