Home Blog Why blown double glazed sealed units need replacing

Why blown double glazed sealed units need replacing


If and when condensation forms on double or triple glazing it tends to only form in 1 of  3 locations. Firstly, either, 1) on the inside of the inside glass pane, or 2) in-between the 2 glass panes or 3) on the outside of the outside glass pane (the latter tends to appear centrally with a clear “picture frame” effect surrounding it.

You can spot when double glazed or triple glazed sealed units have broken down if moisture or “misting” appears in-between the 2 or 3 panes of glass. Any slight moisture or misting on the inside of the sealed unit means it needs replacing, as it is no longer forming a thermal barrier between the inside and outside, plus once “blown” over time the amount of moisture and misting will increase, making the window look even more unsightly. Once things reach this point, it is no longer a “sealed unit”, so will not be performing it’s intended function, which is to keep the cold out, energy generated by your heating system in and the allow solar gain “gained” to be retained within the room or rooms in questions.

If condensation forms on the inside of double glazing on the inside of the inside glass or on the inside frames, this means there is a ventilation and heating problem within that particular room which needs addressing, as neither window frames or glass window panes are the cause of condensation.

If however, condensation appears on on the exterior of the outside pane of glass, this means the sealed unit is performing exactly as it should, plus you will notice this phenomena disappear during the morning after the sun comes up or temperature rises. This strange effect does not appear all year round, or indeed on all elevations, and often never appears, as it all depends on aspect, height above sea level, local topography etc. It tends only to occur in early Spring and and late Autumn, and when it does, it usually does not last long. Strange as it may seem, but this effect if and when it does occur is actually “proof” the sealed unit is performing efficiently, a fact re-iterated by the Glass and Glazing Federation’s publication on the subject “Condensation – Some Causes, Some Advice“. Much better to have damp forming outside your windows than inside your home!

For UK home owners with contemporary energy rated aluminium or PVCU double glazing, replacing broken down sealed units is simple and easy to do. Most double glazing suppliers and installers fitting new products should provide you with a ten year sealed unit guarantee, as replacing them is not inexpensive, so it is worth partnering with a local well established company in your region who provides this customer service as standard with no call out fees for the first ten years. Also if replacing sealed units, ask what guarantee the company is providing on these, as you ready want to be using a company that will be around for the guarantee’s duration, with up to 5 years being the norm for replacement sealed unit warranties.

Dwellings with very old fenestration systems or timber double glazing many find replacement more costly, especially if the units are secured in the frames with putty rather than wooden beads. The problem with wooden beading is that it can break when it is removed in order to replace the existing sealed unit, and exact matching wooden bead in the same profile and staining as the existing beading may not any longer be available.

While replacing glass sealed units that have broken down is not as urgent a priority during the warmer summer months, but it is important to have the work done in the early Autumn, and certainly prior to the onset of Winter, as blown double glazed sealed units are leaking expensive energy out from your home into the environment, making your heating system work harder than need be, and increasing your energy bills. Failed sealed units can be very unsightly, making a property look uncared for, so all in all they are worth replacing to make the windows and/or doors once again energy efficient and sightly.

GGF Members Hazlemere Windows provide a replacement sealed unit service for PVCU and aluminium double glazed and triple glazed systems, whether or not the products were purchased from them or not. They do rightly give priority to their existing customers under guarantee as you would expect, so if you don’t mind waiting a few weeks they are happy to replace blown or cracked double glazedand triple glazed sealed units, plus if you let them have the height and width of each sealed unit, they will give you a no obligation quotation over the phone and then confirm it by email if it is of interest. Get a free no obligation replacement sealed unit quotation from Hazlemere Window Company’s Service Department


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