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0800 772 3318

Lines Open 7 days A Week

0800 772 3318

Lines Open 7 days A Week

Replacing Blown or Misty Sealed Units

What is a Broken Down or Misted Up Double Glazed Unit?


We all know that a Double Glazed Unit consists of two panes of glass with a void in

the middle, all packaged as one single unit. Misting up of a unit is essentially where condensation creeps into the void in the middle causing an unsightly appearance.


This worsens over time until you can no longer see through it clearly (see photo).

It becomes extremely apparent when the sun shines on it, just as it is painfully obvious that your windows are dirty when the sun shines directly on them



Why Do Double Glazed Units Mist Up?



The main reason why a double-glazed sealed unit can mist up (or ‘break down’ as it is referred to in the trade) is due to premature failure of the perimeter seal, which is obviously dependent on how the sealed unit was originally made.


Also, another reason for a double glazed unit misting up is dependant on how the framework it is fitted into was made or how the double-glazed sealed unit was fitted into the framework.


Additionally, severe weather conditions such as wind and rain as well as some cleaning chemicals can have an effect on the Double Glazed unit over time.

What actually happens is the perimeter edge of the unit loses its integrity and lets in moisture somewhere. Initially it may only be visible when the sun shines directly on it and heats the moisture within drawing it upwards and thus appearing as condensation.


It will however, worsen over time until the unit is described as being totally broken down. The only simple and cost effective answer is to replace the double-glazed sealed units with new ones. We are not talking about replacing the

window frames themselves, just the glass (the Double Glazing). There will be no alteration to the existing framework. It is useless trying to separate the 2 glass panes to then remove the condensation, as the sealed unit is factory made

with the panes bonded together to last a lifetime.


Window Manufacturers however do offer guarantees for windows and glazing but the reality is that manufacturing companies come and go throughout their guarantee period and can therefore be sometimes hard to trace. 


Insulated Conservatories are able to replace all styles of doubled galzed sealed units and upgrade them to the latest energy efficient 'A' rated units.


We can replace:


Toughended Glass units

Georgian Grille Units

Leaded Fanlights

French Door or Patio Door units

Any Size Air Gap

Any Size Panes


All with a 10 year guarantee.






Type of Glass Available


There are lots of different types of glass available and below is a brief description of the common ones.


Standard clear glass

This glass was the first and only type to be installed in millions of houses throughout the years and is fast being replaced with more thermally efficient versions.


Low E/K glass

This improved glass (in comparison to Standard glass) has an increased environmental performance with less CO2 emissions and better thermal efficiency and nowadays it is compulsory (to comply with Building Regulations) to put Low E/K Glass into NEW houses. It is also good practice to try and replace windows in existing houses with Low E / K glass but this is not always practical. The reasons being that K glass has a slight tint to it and it will not match the rest of the property if the remaining windows has standard glass. But, if you upgrade all your windows to the more efficient K glass, you will benefit from reduced energy bills. You wil obviously only replace them all for K glass if quite a few of your existing windows have already broken down. Both of the above types of glass, including patterned glass can come as Toughened Glass


Toughened glass 

is exactly what it is described as – toughened or tempered. It has been manufactured by controlled thermal or chemical treatments to increase its strength compared with normal glass. It will usually shatter into small fragments instead of sharp shards when broken, making it less likely to cause any injury if smashed.

From The Building Regulations 2000 – Safety In Relation To Impact, Opening & Cleaning Approved Document N


Critical locations

In some areas and at certain heights, toughened glass will be required to be used and the best place to check all this information is in the above Building Regulations and this can be downloaded Free Of Charge at: http://www.communities.gov.uk/publications/planningandbuilding/buildingapproveddocumentn.

This website address was correct at the time of this report being published. For information only, these ‘critical areas’ are generally between finished floor level and 800mm

above that level in internal and external walls and partitions AND between finished floor level and 1500mm above that level in a door or in a side panel, close to either edge of the door. Please refer to the Approved Document N (as mentioned above) and you will see clear diagrams in the Building Regs detailing this


Free Quotation Service Available

0800 722 3318

To get a free quoytation on replacing any sealed units in your property,

either call us direct with the measurements and details or we are pleased to have a representative visit you to take the measurements and work you out a FREE quotation and discuss the best options in terms of the type of replacement glass which would best suit your requirements.

We are pleased

to quote for

1 to 100 replacement

sealed units.