Haze with Low-e Windows
I am located near Ottawa, Canada.
Why can’t I find more complaints about the ugly haze created by low-e coatings on windows?
We recently had new windows installed and when the sun shines directly on them, we see a very distinct blue haze. The company rep that sold us the windows said we would have a blue tint on the windows, but he did not mention a haze. Apparently, this haze is the result of the manufacturer’s low-e coating, applied to meet Energy Star standards.
We find this haze to be totally unacceptable, as it is quite ugly and reduces visibility through the glass by about 20 percent and it is impossible to see into shaded areas outdoors. It makes us want to close the curtains on beautiful, bright, sunny days!
The manufacturer, North Star, makes an obscure reference to the “possibility of a slight haze” on its website, saying it is “normal.” The installer told us pretty much the same.
As a result of considerable research online, I was able to find just two other complaints about the haze produced by low-e coatings – one of them is on your website (Thu, 09/06/2012) from last year. Is my situation so unique?
I am including a photo I took of our “picture” window, with something placed outside to cast a shadow on the glass to show the difference in view with and without the haze. This photo was taken in October, but a month earlier, when the sun was higher in the sky, the haze was a bit more intense.
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Replies
Matt,
Most window manufacturers don't make their own glazing. Glazing is purchased from manufacturers like Cardinal, AGC, Guardian, Southwall Technologies, or Pilkington.
Each manufacturer makes a wide number of glazing products. Some are crystal clear and have a high VT. Others can (under some lighting conditions) look hazy or have a low VT. In many cases, windows with very low U-factors also have a very low VT.
There is no substitute for examining a window with the glazing you intend to purchase before settling on the glazing for your house.
Matt,
There are two types of LowE coatings applied to glass to improve energy performance; generally referred to as hardcoat and softcoat.
In the US about 80% (give or take a little) of LowE applications are softcoat, but in Canada the use of hardcoats is probably about equal to, or a bit higher than, softcoats due to (with a few notable exceptions) hardcoats being considered high solar heat gain coatings and softcoats being considered low solar heat gain coatings.
The Canadian energy code is written to take advantage of free solar heat gain when needed, whereas US codes usually ignore or even penalize solar heat gain in favor of higher R values in window performance.
All glass used in windows has some level of haze. Even clear glass can show a bit of haze in the right conditions. Although glass feels as smooth as - well, glass - microscopically, glass is actually a bit rough. Haze occurs when incoming light is scattered due to the rough surface.
Hardcoats tend to produce a good bit more haze than do softcoats because as applied they result in a much rougher surface microscopically. So while hardcoats are used extensively in Canada, because of their perceived solar heat gain performance advantage, there is the downside that hardcoats can appear hazy in certain lighting conditions.
Per their website, North Star uses two different hardcoats and one softcoat in their windows - the softcoat for low solar heat gain applications (cooling dominated climates)and the hardcoats for high solar heat gain applications (heating dominated climates).
I know this is an old post and I know you are US and I am U.K., but I have the same problem. Our windows were installed a week ago, the following day was sunny and I was in tears - it looks awful. When I queried it with the installation company I was told the coating was ‘by law’ and ‘learn to live with it’ - gee, that’s great - but if the ‘law’ requires us to have ‘a’ coating - why this one ? Get off your arses and come up with something better!