Vacuum between Glass

spoons · 15th August 2007, 13:20

Someone mentioned to me yesterday that the 'vacuum' in double glazed windows wears off over a period of years... therefore noise reduction is also reduced significantly.

Can you 'reset' the vacuum within your existing double glazed windows or does it just mean that you have to replace them all.

Also, how do you tell how good the vacuum is ?? (no sarcastic comments... oh, go on then....)

**Ste** · 15th August 2007, 13:22

Is it actually a vacuum? Or is it filled with inert gas? If it is actually a vacuum, then the forces pushing the glass panels together would be HUGE.

Can't really see it being a vacuum.

EG, Force = pressure x area

Pressure = 100,000 Pa (N/m2)
Area = 1m2 (for a large single piece - lets just say)

The sealed units can be removed and replaced, without changing the frames. Never heard of sound proofing 'wearing off' after a few years TBH
Force = 100,000 N = = = 10 tonnes of weight approx. Glass would smash.

**john_k_sri** · 15th August 2007, 13:26

Dont think it's the 'vacuum' but the seals which break down/deteriorate. I agree with Ste don't think it's a vacuum anyway, but I'm not sure.

**smithi** · 15th August 2007, 13:31

I thought it was just a sealed unit filled with air or an inert gas, not a vacuum. The seal can deteriorate and moisture become evident in the air space.
The thermal performance and sound proofing is due to the air gap.

I am no expert but thats my penny's worth.

spoons · 15th August 2007, 13:44

Wikipedia...

The air space between the lites may be filled with air or an inert gas like argon or krypton which would provide better insulating performance.

Typically the spacer is filled with desiccant to prevent condensation and improve insulating performance.

Less commonly, most of the air is removed, leaving a partial vacuum, which drastically reduces heat transfer through convection and conduction. This is called evacuated glazing.

.......so the chances are that I've just got air between the lites and my source information was not correct !! there is no vacuum..

**Duncan** · 15th August 2007, 13:57

Basically once the sealed unit has lost it's seal - and either the partial vacuum or the inert gas in it - it's a new sealed unit. I've never heard of anyone refilling the gas or redoing the partial vacuum.

As for telling how good the seal/vacuum is - I don't think you can. One symptom of a sealed unit failing is you start to get condensation between the two panes. Other than that I don't think you can really test it as such.

D

**SignumPhil** · 15th August 2007, 14:29

That's what I thought (having bought new windows recently). They theoretically fill the space with dry air, and the seal has a desiccant in it, to keep the air dry.
If the unit leaks (I believe "blown" is the technical term) damp air gets in, saturates the desiccant and you get condensation inside.
Any repair you could do with be harder and more expensive than a new unit.
If you have to replace it, I'd go for Pilkington K glass, to give better unsulation.

Phil

**Caterman** · 15th August 2007, 16:50

I've just had both panes in the front go and they are starting to condensate up! SWMBO now thinks it would be a good time to change the windows as they have been in for all of 14 years. I said "but they're plastic!" No matter, she'd like a "change"

Women!

By the way they used to fill the gap with "stale air" and desiccant around the edge. ( i sold windows for a short while a few years ago

) No vacuum

Not sure if it's still the same

**G.O'Rilla** · 15th August 2007, 20:09

The only vacuum in our house is the one between my ears. They give me a brain scan every 6 months to prove it............

**simac** · 15th August 2007, 21:54

Originally Posted by Duncan

As for telling how good the seal/vacuum is - I don't think you can. One symptom of a sealed unit failing is you start to get condensation between the two panes. Other than that I don't think you can really test it as such.

Aye, that's the only way to tell seals have failed TBH even then the condensation will only appear during certain climatic conditions. Changing the units is the most economical way to sort it out, while retaining the existing frames.

Also, you would struggle now to find a double glazed unit which isn't K seal (well, the outer pane) as this is a Building Reg requirement which all of the manufacturers, to my knowledge, apply to all their products.

Normally hardwood double glazed units fail earlier than uPVC, i've seen some poor quality h/w windows fail at 6 years old.