Blown windows effect efficiency in a bad way!

Blown windows effect efficiency in a bad way!

In terms of a window, efficiency is measured by their ability to keep the weather out and the warmth in.

The more efficient the window the better they are at doing the job they were designed for.


If a window was leaky and drafts were constantly blowing round their edges then their efficiency would be rather low.  On the other hand if we have a well fitted window which keeps the wind out and the warmth in then the better they are.


But how do we know if a window is not as good as the day it was installed?


The most obvious giveaway is the misty window.  A misty window, or another term given is blown window, is where the air gap between the panes is no longer a sealed area.  The seal has become compromised and warmer, damp, air has managed to get in.  When there is a difference in temperatures between the outside world and the inside we get condensation on the external pane of glass that we can do nothing about, at the moment. Frustratingly we have to wait for the panes to warm up before we can look out without everything looking foggy.


A blown pane has reduced efficiency because the idea of the double glazed unit is no longer true.  The design of the double glazed unit is such that the inner and outer panes of glass are separated by a gap.  This gap can be filled with gas or it can simply be air.  An important aspect of this design is that the gas or air does not get exchanged with air from one side or the other of the double glazed unit.  If it does then the result is the blown, misty window.


So why double glazed?  The two panes help to maintain thermal stability between the external, usually cooler, pane of glass and the internal, warmer, pane.  Within the gap the temperature difference is balanced between the two sides.  However, the internal temperature can be a lot more stable.


We can increase the comfort within a room by using newer technologies such as low-emissivity or low-E glass.  This is where the internal pane of glass has a coating which reflects back more of the heat that is attempting to escape through the window.  Warmth from the sun can come in but cannot escape the same.  These double glazed units may have a higher initial cost but the longer term benefits may outweigh this cost.  Low-E glass may also cut down on ultra-violet light too.  Ultra-violet light is the one which does the damage to items in its direct glare.  Fabrics can become faded for example.  Cutting this light out to begin helps to preserve the items we cherish.


So we can look at that steamed-up, misty window and say it has blown.  But we need to make sure that it is truly blown and not just steamed-up.  During the cooler nights we wake up in the morning and the window has condensation on the inside.  We should be able to wipe this off with a towel, there is a good chance that this condensation is all over the pane.  So we know this is a misty window which is all well and good.  


If we look at the window and try to dry it off with the towel but we are not having any joy at wiping the condensation away then we have the blown window option.  The only choice we have is to wait for things to warm up and the condensation to dissipate.  The problem here is that it will keep returning and the only option is to get the double glazed unit replaced.  Another challenge we are going to have is it will begin to feel cooler in the room because the efficiency of the glazing unit is going to be quite low.  It may feel like the cooler air is pouring itself into the room.  It may not be a draft, unless there are issues with the frames or any window openers you may have.  The pouring effect is where the colder air is flowing down the window and into the room.  Hot air rises so the colder air manages to get underneath and if you are standing near the window it feels like the outside cold air is being poured into the room as it flows down the window across the sill and down the wall.


This begins to cost more because you feel cold, you put the heating up a little bit or it stays on for that little bit longer, but the cooler air still flows down and the warmer air rises.


At this point it may be the best option to bring in a professional team to check out your double glazed unit to see what can be done.  A blown window would have to be replaced.  The uPVC specialist coming to take a look at your window will want to check what may have caused the problem.  If it is a simple age related failure then arrangements can be made to replace the double glazed unit.  For a damaged window the same applies as long as the damage has not been caused by the frame which is damaged too.  If the frame is repairable then that would need to be sorted out first otherwise the new glazing unit will suffer the same fate.  Should the frame itself be too damaged then it would need to be replaced also.


A window frame design also helps with thermal efficiency too.  When you are looking at replacing your double glazing or indeed installing new double glazing, you should inquire about the rating of the frame too.  Within the frame there are security measures and the frame has air pockets which act in a similar manner to the double glazing unit.

If you’re interested in replacing a window for your home, take a look at our New Window packages. Alternatively, just take a look at our other services for more!

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