WHAT CAUSES MISTED DOUBLE GLAZING (AKA BLOWN SEALED UNITS?
Double glazing is created by sealing two panes of glass together, with a gap left between them, to form a double glazed unit. The air held inside the window, creates an insulating barrier that keeps heat in.
If the the seal on the glass should break (or fails, as its known in the industry), condensation can get into the unit which causes a misted up window. The seal can break for a number of reasons, but is mainly due to the age of the window (seals don’t last forever), how it was manufactured or even how it was fitted in the first place.
SHOULD I REPAIR OR REPLACE THE MISTED WINDOW?
Repair misted windows: some companies may advocate drilling a small hole into the unit, blow in warm air to clear the condensation, and then fill the hole. While this may work for a few days or weeks, the problem will return as the seal has been broken.
Replace the window: there is no need to replace the entire window, as long as the frame is intact. You only need to replace the sealed unit and, if you upgrade to Low E glass, the insulation will be even better.
The only recommended way to permanently fix misted double glazing, is to replace the sealed unit. This is far less expensive than a new window, and the new sealed unit will come with a warranty.
BUT I HAVE MISTING ON THE OUTSIDE MY WINDOW?
We usually see this happening in Autumn or Spring. This is because the temperature of the glass drops to a low level overnight, with the moisture of the morning’s heavy dew condensing on the cold surface of the glass.
You’ll often see this happening more with newer windows, and Low E glass, as the windows fitted nowadays are far more efficient than those fitted a few years ago.
However, there is no need change the glass or think about replacing the window, as this is just down to the weather and actually shows that your windows are working correctly.