Low E glass - are you using it, pros and cons

Hi there

Just looking at pros and cons of using the Low E glass. We are signed up to build and I mentioned I would love DG but it would be out of our budget. The sales guy said they do Low E glass and if after looking in to them I was keen it would be around 3K. Is anyone else using it?

Only in Australia is low-E offered in single glazed. It is difficult to clean, prone to spontaneous fracture due to thermal shock and doesn't work in any way like double glazing. IMO a waste of money. Did you price double glazing?
Ed

Agree with Ed,

Any external coating on, even if on a Double glazed unit is a real nuisance.

Whilst it will give you better thermal properties it will become 'dirty' noticeably quicker due to the surface of the coating and will also be very difficult to clean (and easy to damage whilst cleaning). Thermal fracture will only be an issue if it is exposed to partial shading and wont be an issue if its toughened, but not every unit will be toughened so not worth the risk in single glazing. Thermal fracture isn't covered under warranty either.

Thanks,
Kurt

Agree with that, thermal fracture is also caused by the temperature difference of the coated surface versus the uncoated surface, caused by heat absorption on the coated surface, which causes differential expansion and stress between the 2 glass lamina.

Also worth a mention that in double glazing, the low-E is not laminated and therefore not prone to thermal stress and fracture, furthermore the coating is usually an efficient soft-coat on the inside of the double glazed unit. So not dirt, and no cleaning problems.

Ed

My neighbour installed it and in the end just wishes he had spent the money on DG.

Thank you for the information. We haven't priced up DG just yet and we would love to do it if at all possible. Our last home in NZ had it as it's now part of the building standard (thankfully they have cottoned on to the fact they need to build for the climate). I think we will skip the low-e then and look in to DG. I guess it would be difficult to estimate but for a 5 bdrm, 2 living house that is around 230sq, what sort of cost would we be looking at?

Ive only seen it once but thought it had a blue tint that i hated that was comfort plus neutral

Ok I'll explain about Low-E (Viridian is the only producer of hardcoat Low-E in Australasia)

Low-E is a type of coating designed to reflect infrared (heat) to boost the insulation performance of glass.

There are two types of Low-E that are available ON glass:

1) Hardcoat Low-E - this is a metallic coating applied to the glass when the glass is being made at the float glass furnace. The coating is applied while the glass is still semi-molten. It permanently fuses to the glass and becomes part of it. The coating is metallic and is very durable. It is the only type of coating that can be exposed to contact (on the inside surface of the window). Benefits - fits in standard window frames, affordable, gives a good energy efficiency lift over ordinary glass. Negatives - gets dirty easier and can have a slight 'haze' when sun strikes it at certain angles/times of year. Not as good as Double glazing.

2) Softcoat Low-E - this is a coating applied to glass after it was made. There are different ways to apply the coating but the most common is sputter coating (think electrostatic spray painting). This coating is durable but fragile. It needs to be sealed inside a double glazed window to protect it. You can also get double glazing with Hardcoat Low-E inside.

SO - Hardcoat Low-E is available in Australia in two forms:

Laminated Low-E glass (two sheets of glass stuck together with a layer of plastic in the middle so it looks like one sheet of glass) and the Low-E is on the inside face of the glass - Viridian's product is called ComfortPlus. Benefits - fits in standard frame, blocks most UV, is already a grade A safety glass. Negatives - if using for sun load such as west facing windows, need to do a thermal assessment to determine if it needs toughening to resist the thermal load, as untoughened laminated glass is more vulnerable to thermal fractures. Toughening laminated glass is more expensive.

The other is just the single sheet of glass with Low-E fused to it (as it came from the furnace) - Viridian's product is called SmartGlass more info on that link if interested. Benefits - fits in standard frame, affordable, easily toughened if additoinal thermal protection is needed for toned/tinted windows.

Both of these fit into a standard window frame. Hardcoat Low-E in single glazed forms like these are designed to be a cost effective step from ordinary glazing, but you do get a greater benefit from using double glazing. Hardcoat Low-E does get dirty more easily than plain glass, but it is very durable and resistant to damage as it is a metal coating. Most people mistake marks as damage, when actually many of them can be removed. For example dog claws or even a coin scrapped over the glass will leave a mark, but it is the claw or coin metal being left behind ON the Low-E coating, not the coating being damaged. Obviously anything that would damage the glass would also damage the coating (no diamond rings please!) There are cleaning instructions for all Low-E hardcoats on Viridian's website. A good product for day to day cleaning of Low-E is actually Windex Multipurpose clear. Very important to wipe the window dry after wetting and wiping it.

Ultimately if you can afford it, we recommend double glazing, but if you are on a budget, Low-E single glazing can still give your home a good insulation boost over using ordinary glass.

Hope this helps clear things up

Good stuff, can you also give the relative performance (U value) of hard and soft coat low-Es.

Thanks
Ed

OP, where do you live and what are you trying to achieve with Low E glass? This is important information when it comes to Low E.

For example, Low E is not recommended for sun control in Melbourne. This is because Low E glass only works in one direction - depending on which way you install it, it either keeps the heat IN your house or it keeps the heat (of the sun) OUT of your house. You can see that in some climates, this means that any benefit gained in the warm months (keeping the heat of the sun out) might be lost in the winter (because you get solar heat gain from your windows).

If your plan is to use it for insulating (i.e., keeping your house warm in winter), my understanding is that Low E is a compliment to DG, and not really an alternative. If you are worried about keeping heat inside in the winter, you might consider your window furnishing choices and include pelmets and drapes, or pelmets and well fitting roman blinds. eScreen type roller blinds also claim to have insulating properties, although I have my doubts about these. Another option is honeycomb blinds, which trap air between the layers and can add an insulative layer to your windows. Consider that you will probably need to purchase window coverings anyway, so making smart choices with these could be a good solution for little to no additional cost.

The good thing about window furnishings is that it allows you to keep your North facing windows uncovered in winter during the day, to collect lots of free heat from the sun. Then you can close them up tight at night to keep all that heat inside overnight.

This is the one thing I recommend low-E is suitable for in Melbourne.

Ed

Low - e glass. Pfft. Sure it works, but we now regularly supply triple glazed windows, and our customers have been very impressed; the difference between single low-e glazing and ordinary double glazing is like night and day; but the jump from double to triple glazing takes the performance into the next dimension!

There is nothing that the glass supplier can do to the glass - low-e it, tint it, low-e and tint it, fiddle with it, tweak it etc that will ever come close to matching the performance of ordinary double glazing. Incidentally, overseas research indicated that double glazing with low-e on both sides and a gas infill attempts to replicate the effectiveness of triple glazing, but actually triple glazing is less expensive and more effective!

Low-e glass eat your heart out!

Think of Low-E as a heat mirror for radiant heat. So it works in summer to help keep heat out but also in winter to keep it in the house. It is a lot better than ordinary glass, but double glazing or double glazing with Low-E are even better performers for keeping your home comfortable. FYI North facing clear windows with Low-E also work with passive solar heating / thermal mass.

Agree with some of what you said and disagree with other parts of it.

Agree about double glazing being superior to plain low-e. But for people on a budget, having windows with low-e is still a decent step up and energy savings vs ordinary glass. Also I agree that triple glazing is a premium product and has generally superior conductive insulation benefits over double glazing...

However most of Australia has to deal with summer heat issues. In this case whether it is single/double/triple glazing all are useless at stopping direct sun / radiant heat without either tint in the glass or an energy efficient coating.
For most climates around Australia, double glazing is sufficient (no severe colder temps like in Europe).

Look at almost every quality commercial building around Australia and you will find it has coated glass in a double glazed unit...

Now if you were trying to build yourself a 9 or even 10 Star energy neutral home... then bring on the best

Hi Ed,
Sure - but remember that softcoats can only be in a double glazed unit. Here are some rough guideline numbers for the glass only peformance (window frames can affect this number as you'd know )

.......................................................Rough U-Values (glass only)
Ordinary Glass........................................................ 5.8
Hardcoat Low-E in single sheet.................................. 3.5-3.8
Double glazed unit (no Low-E)...................................... 2.7
Hardcoat Low-E in double glazed unit + argon gas.............. 1.6
Softcoat Low-E in double glazed unit............................. 1.6
Softcoat Low-E in double glazed unit + argon gas.............. 1.3
Softcoat Low-E in double glazed unit + argon +hardcoat...... 1.1

Sure, Viridian, that's all good and fair, but if a customer had a solar gain issue, ideally they would utilise an outside form of shading eg roof/awning/trees/neighbouring property etc; for it is also true that ANY OUTSIDE FORM OF SHADING WILL PERFORM MUCH BETTER THAN ANY GLASS TREATMENT, won't you agree? A bit of strategic planning goes a long way when it comes to windows...

By the way, we love your Pyroguard 40 product, our windows are BAL40 compliant when used in conjunction with Pyroguard 40!

Totally agree. Stopping heat from getting into the building is best. External shading/eaves/shade devices, etc all help.

Thank you for the information. It certainly gives food for though and has given me some points to think over. We have been told that we need to get a 6 star energy rating and to do that we have been presented with four options, one is to use low e glass and increase insulation. It bugs me that we are told this now and it wasn't allowed for in the quote we got but building seems to be a minefiled of extra costs. It sounds like DG is the go, not sure we can afford it but I also don't know how it compares price wise. Is it worth putting DG on the main large living areas but not applying it to all windows? I am taking on the point that preventing sun from entering is a major factor and we intend to do this by having our alfresco area extended to provide more shade. It seems that taking the alfresco off was a suggestion on how to meet the 6 star rating so that confuses me more. I will have to speak with the guy about this. We are building in Adelaide Hills so we have the extremes of hot weather in the summer but cooler weather in the winter. The temps range from 42 to -2.

To reduce solar heat gain, best option as mentioned, is shade the window, second best is to use low-E, IMO only in double glazing. Double glazing on it's own has no effect on solar heat gain. In single glazing low-E can suffer from thermal shock, and is difficult to maintain. Plus if you use double glazing it will help with the -2 temperatures.

Double glazing in one area will aid the conservation of heat inside the home, it won't help solar heat gain.

I would say that you live in a primarily heating area in the energy rating software, and taking the alfresco off aided the heating component at the expense of cooling. It's based on averages and statistics, so, like the man with one leg encased in ice and one in boiling water, on average he was comfortable.

Ed

Agree with Ed. If you are trying to reduce the direct sun passing through glass by using tint/colour, thermal stress is created due to heat build up or temperature differences across the glass. Tinted glass may need to be toughened to resist thermal breakage. You should have your glazier do a thermal assessment of the windows. This generally applies to both single and double glazing. Low-E coatings will increase the thermal stress on tinted glass too.

In Hills_kiwi's case with that temperature range, I'd also recommend double glazing with Low-E where you can afford it and single glazed Low-E where you are in budget mode!