All about misted windows

Misted windows are usually referred to as broken down sealed units. These pictures show the results of having broken down sealed units. The sealed unit is the two panes of glass sealed together around a spacer bar before going into the window frame.  These sealed units should be just that - sealed - airtight and watertight.  If a gap appears in the seal then when the sun shines on the glass the air inside expands with the heat, forcing the air out of the unit.  When the unit cools down again the opposite happens and air is drawn into the unit.  Moisture in the air then sticks to the inside of the unit making it cloud over.  This can come and go at first but eventually it will be saturated.  If the unit is actually sitting in water in the frame then it will draw the water in as well and I have seen some units that resemble a fish tank.   There are basically two main reasons why units develop a rupture in the seal and 95% of the time it is either one of these or a combination of both.   

The first is down to drainage.  If there is insufficient drainage in the frame then the units could be sitting in water.  Even though they are sealed from air and water they are not designed to be sitting in water. (It’s a bit like a water resistant watch that would be OK in the rain but you wouldn’t go swimming in it unless it was a divers watch.)  The water eventually breaks down the seal and the moisture gets in.   This happens even more quickly if the units are not sitting on glass packers to leave a gap between the unit and the frame. 

The second reason is due to the two panes of glass not being on a solid and even base. They are supposed to be set solidly on glass packers of the correct width for the unit and that packer needs to be level.   If not then over time the two panes will slide apart and cause a tear in the seal.  I commonly see a 24mm packer under a 28mm glass unit and only one pane of the glass is on the packer.   

When we change sealed units we always identify the causes of them failing and show the customer. We then deal with these causes so that the new ones don’t fail for the same reasons and we guarantee all our new units.  We have even seen units that were only replaced 12 months earlier that need doing again because the causes were not dealt with by the people who changed them.   

We are often asked about drilling holes in the glass and sucking the moisture out. There have been companies advertising that they do just that.  (They also claim to put a valve in one of the holes so that any new moisture will magically leave through that hole!)  I have several issues with this.  Firstly, if you have a hole in your sealed unit then you basically do not have double glazing.  It needs to be sealed to get the thermal benefits.  Secondly if you don’t deal with the causes then the moisture will just keep getting in anyway.  Thirdly – and most importantly – I have never seen this work.  I have changed many units that had this done to them and they were still misted up and the customer had paid for this and then had to pay for new units anyway. And of course if it did work I would be doing it myself and save the hassle of buying new glass!   

If you want the problem of misted windows sorted out once and for all in the most cost effective and professional way, just give us a call.