# K Glass Versus Vistatherm



## Bill (17 Jul 2006)

Can anyone tell me which is better to use in double glazed windows K Glass or Visatherm?


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## NHG (17 Jul 2006)

You should view www.pilkington.co.uk "low-E" is way better than "K Glass" - Vistatherm is actually the name that carey's sell their glass under i.e tayto, walkers, kingcrisps etc.

If a standard D/G Unit is 0% a K-glass unit is 36% better than the standard unit and a "low-e" unit is 164% better than the standard unit again  - I picked up those % up from [broken link removed] .  An argon filled "low-e" unit gives a U Value of 1.1 w/m2k and an air filled unit a U Value of 1.4 w/m2k.

I have "K-glass" in my own house ("low-e" was'nt available then 7yrs ago) and it scratches very easily.  Where I work we use all "low-e" and I have'nt come across problems with scratches on the "low-e".  At work we use Wexford Viking Shield "Optishield".  It is available in standard units and in Toughened Units.


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## ninsaga (17 Jul 2006)

Hopefull this is not a 'how long is a peice of string' question... but for standard, v's K glass v's low-e, & low-e argon filled .. what are the typical diff in cost eg 

vista = standard + 5%
low-e = standard + 8% 
etc etc..

Anone go a quote lately across all types & could share their findings?

ninsaga


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## NHG (17 Jul 2006)

By Law all new glazing should be "low-e". Where I work we purchase "K" and "low-e" for the same price and I therefore I tell customers about both and I don't thing that I sold even 1 "K" unit in the last two years! Why would someone buy "K" when you can get "low-e" for the same price. 

We all need to be aware of U Values - Especially with the way fuel costs have risen and are still on the way up! We even have to pay an Energy Surcharge on all glass that we buy.

The difference between a standard air filled obscure D/G unit and an air filled obscure "low-e" D/G unit is 40% (probably less now as price for standard unit was feb '06 and "low -e" was last week and I know that standard price went up about a month or two ago and "low-e" did not)


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## ipxl (17 Jul 2006)

I am very interested in this comparison too.
I'm based in Mayo and the DG/window company who I've been
recommended (and whom I've received a fairly detailed quote
from) told me they do K glass but haven't yet glazed with argon-fill
windows. The rep seemed to equate K glass and low-E glass.
I spoke with another supplier (Wrights Milltownpass) who were
very helpful but they are too far away for practical purposes for
a domestic install and customer after care based on our location.

Does anyone know a supplier in the west who supplies and fits
low-E/argon filled DG ? I'm inclined to stay with my current
supplier of choice other than for the reason that they seem
to be using glazing which would seem a bit dated compared
to the current state of the art.

Ipxl


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## NHG (17 Jul 2006)

As I am in the south-east and I use Viking Shield Glass and am delighted with both the service and quality of the units.

I don't use the argon filled units unless it is requested which is very rarely, I use air filled.  Argon-filled units are another 5% dearer than air-filled. It is all Hardwood Joinery that we manufacture and would have a higher U Value to start with anyway.

Gas evaporates????   So how long would it last inside the D/G Unit?


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## Zutz (17 Jul 2006)

Just wondering, I am thinking of using Senator Windows and they use K Glass Argon filled. I was under the impression that Senator would be considered one of the better windows, window providers, if they are? why do they not use Low e instead of K Glass?


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## ipxl (17 Jul 2006)

I spoke to the quality department of another (well known) DG supplier.
Quite helpful.

K glass is one of a numbe of "low E" glazing products (it happens to
be the Pilkington trademark). As far as I can see the term is 
used quite liberally and sometimes (erroneously) interchangeably
with the more general term "low E".

I'm just passing on the info I got from that supplier's quality dept:

This supplier provides two types of low E coatings. One is a hard
coating 1.4 w/m2K window and window + frame weighted avg of approx 1.9
The other is a soft coating which gives 1.1 w/m2K and weighted avg
of 1.6 w/m2K (window + frame).
The soft coatings are more recent to the market. They require a lot
more tender loving care during production but coating durability is
less of an issue when installed because the coating is on the inner
side of the inner pane and isn't exposed to the elements.
The cost is approx 15% more for the soft coat (better U value) low E
because of the labour intensivity involved in that coating making
it through production.


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## ipxl (17 Jul 2006)

.. and one other piece of information.

As regards dispersion of the argon gas from the cavity.
The suppliers QC folks say that under most conditions the initial fill
by volume in the cavity by argon will be approx 90% or therabouts.
The tolerances are specified such that no more than I think 2% 
of gas can disperse per annum from the cavity so I am guessing
after 20 yrs no more than 40% dispersion may have occurred.
I guess this means that one can expect that the efficacy of
the argon fill remains for most of the useful lifetime of the windows.

~ipl


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## z102 (18 Jul 2006)

Get used to the facts and numbers, ask for the U-value and not for the brandnames. As NHG mentioned already: the building regulations demand a certain U-value which can be achived by using metallcoated gasfilled doubleglazed panes. One could legally get away either with the gasfilling or the metallcoating by using triple glazed panes.


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## Monty G (24 Jul 2006)

If given the choice you should opt for the soft-coat rather then hard-coat. Soft-coats give lower U-values which means less heat transfer – less increasingly expensive warm-air going out the window. Additional advantages are better clarity – K glass can show ‘haze’ under certain conditions, lower heat-gain – important in sun-rooms and large south-facing windows, and significantly UV transmission – less fading of fabrics and wooden floors.
As is clear from the thread there is a lot of confusion about the different coatings. Hard-coats (such as Pilkington ‘K’) are medium performance coatings. The tin-oxide coating is applied to the semi-molten glass and is ‘baked’ on. This ‘hard’ coated glass can be handled pretty much like any other glass and the coating can even be exposed and (gently) cleaned.  Soft-coatings, typically silver-oxide, are applied to cold glass in a vacuum sputtering chamber. The coating is much finer then the hard-coats and requires more delicate handling. This results in only a couple of Irish IGU suppliers being equipped to deal with it at the moment  It has been commonly available in northern Europe and north America for more then a decade. 
As a rule of thumb a well made double-glazed soft-coated window will have a better energy performance then an un-coated triple-glazed window. 
Anybody buying windows should ask for the whole window U-value and not just the glazing alone. Ask for independent certification as the sales people generally don’t know much about this and have a tendency to make things up as they go along.


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## ipxl (25 Jul 2006)

Monty G said:
			
		

> If given the choice you should opt for the soft-coat rather then hard-coat. Soft-coats give lower U-values which means less heat transfer – less increasingly expensive warm-air going out the window. Additional advantages are better clarity – K glass can show ‘haze’ under certain conditions, lower heat-gain – important in sun-rooms and large south-facing windows, and significantly UV transmission – less fading of fabrics and wooden floors.
> As is clear from the thread there is a lot of confusion about the different coatings. Hard-coats (such as Pilkington ‘K’) are medium performance coatings. The tin-oxide coating is applied to the semi-molten glass and is ‘baked’ on. This ‘hard’ coated glass can be handled pretty much like any other glass and the coating can even be exposed and (gently) cleaned.  Soft-coatings, typically silver-oxide, are applied to cold glass in a vacuum sputtering chamber. The coating is much finer then the hard-coats and requires more delicate handling. This results in only a couple of Irish IGU suppliers being equipped to deal with it at the moment  It has been commonly available in northern Europe and north America for more then a decade.
> As a rule of thumb a well made double-glazed soft-coated window will have a better energy performance then an un-coated triple-glazed window.
> Anybody buying windows should ask for the whole window U-value and not just the glazing alone. Ask for independent certification as the sales people generally don’t know much about this and have a tendency to make things up as they go along.



Monty - this is excellent info. It rolls up very succinctly what I have found
by digging around and getting the info piecemeal from the suppliers.
Wrights in Milltownpass were helpful and gave me a lot of info similar to
what you have mentioned here. The only trouble is that they are too far
to be practical to fit/supply our windows.

My dilemma is that the supplier with best reputation locally just do 
K-glass or something akin to hard coat/low E with no argon fill.
The other option is a much larger outfit who I've heard questionable
info regarding the standards of their fitters. They definitely do 
soft-coat/low E and argon fill but I'm wondering if I'd risk getting
them to do the job because there is nothing worse than paying for
a high spec window and having it poorly fitted and having the 
damp course material around the cavity destroyed by potentially
sloppy fitters,etc. Do you know of a supplier who will fit in Mayo
who does soft coat low-E. Drop me a PM if you do ! thanks!!!

-ipxl


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## Garry (10 Feb 2007)

There seems to be lots of misleading advice on this topic.  If you make some enquiries then you find that the Pilkington low e glass they call Pilkington K Glass is as good as the soft coated low e products with benefits to the producer.  Soft coats are more sensitive to use in a factory.  If you look at the comparative U value of each product then on the face of it one looks better than the other but once you put the glass in a window and measure the total performance then the total energy loss through the window is about the same.  K glass lets more heat from the sun into the house (and that's free) than the soft coats.  The U value is only half the picture.  If you use the lower U value products then you increase the risk of having condensation on the outside of the windows.  Pilkington K Glass is the registered trade name for the Pilkington product.

It is time that people started looking at the total energy position.  Much of the information is in the window energy rating site (www.*bfrc*.org) where windows are rated like other domestic appliances and graded with a letter.  If you have to comply with building regulations that use carbon emission calculations you will find they ask about window U values and g value.  The g value is a measure of the ability of the window to let heat in.

I hope this helps.


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## macnas (10 Feb 2007)

The sliding doors in my house have misting in the cavity between the   2 panes of glass. Is it possible to remedy this? Expensive? The seal must have deteriorated. Is it easier to replace the glass? It is approx 1m x 2m


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## santiago (12 Feb 2007)

I've got old sash windows in a listed house so I can't double glaze them. However, some panes are cracked and need replacement, so I'd like to fit the most energy-efficient glass possible. I presume I can't use the coated glass because the coating would wear off with cleaning etc. (not being on the inner side of a DG unit), so what's the best glass I can get for single glazing?


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## ACA (12 Feb 2007)

> The sliding doors in my house have misting in the cavity between the 2 panes of glass. Is it possible to remedy this? Expensive? The seal must have deteriorated. Is it easier to replace the glass? It is approx 1m x 2m


Just been talking to hubby who works for a window company in Waterford - the seal has broken down, only way to fix it is to replace the glass. If your windows are less than 5 years old, try going back to the place of purchase - most window companies guarantee the glass for minimum of 5 years. If not, hubby reckons your looking at approx €500 to replace the glass.


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## NHG (13 Feb 2007)

I would recommend 6.4mm laminated glass if replacing single glazing to you Up & Down Sliding Sash Windows - the only thing to check is, will the weights be able to cater for the extra weight!

When D/G was a new product many many moons ago 6.4mm lam was thought to be about 75% as good as what we now call standard D/G - but now we have experts show that soft coated D/G is 164% better than standard D/G!!


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## santiago (13 Feb 2007)

Thanks NHG.

If it's much heavier than the existing glass, presumably the counterweights could be adjusted to account for the extra weight in the windows? Or is this a non-runner?


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## S.L.F (17 Oct 2008)

NHG said:


> I would recommend 6.4mm laminated glass if replacing single glazing to you Up & Down Sliding Sash Windows - the only thing to check is, will the weights be able to cater for the extra weight!



I just came across this thread.....

Sliding sash windows *should not* have heavier glass put into them they should only have *2 or 3mm* glass installed depending on the original glass.

If heavier glass is used it could easily damage the sashes.

See here and on page 25  it says,

_If using float glass, order 2mm or 3mm thick glass in preference to 4mm or thicker. Using thicker glass than the original, which could be less than 2mm thick, will weigh down the sash and can strain the joints of delicate sashes._


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