RE: Low E argon filled windows, i was always under the impreession that you
had to choose which emitting style was right for your area. Did you want to
keep the heat and sun out or the heat in? This dictated which side the
coating was placed on the glass? In your comments, are you suggesting they
work both ways, always reflecting the hotter side? If so, how does it do
that?
regards,
Low E Glass - It Really Works!
Summary: Windows with low e glass can help stop the loss of heat from your home. Window treatments with ultra thin metallic coating in the glass is the answer.
Related Articles: Low-E Glass Fading, Low-E Glass Manufacturers, Types and Benefits
DEAR TIM: My husband and I will be building a new home soon. Our windows are available with optional low-E glass. Just what is low E glass? Does it really work? Are there different types? Will it block ultraviolet (UV) light? Is the argon gas necessary? Do you think it is worth the extra money? E. R.
DEAR E. R.: Window glass was revolutionized in the 1970's. Insulated glass (two or more pieces of glass with a dead air space between) made its debut in the early 70's. Low E glass was introduced in 1979. The E stands for emissivity. Low E glass works by reflecting heat back to its source. It does this by utilizing an ultra thin metallic coating on or in the glass.
Among other things, sunlight contains visible light, UV light, and infrared (IR) light. Visible light enables us to see things. Ultraviolet light damages your skin, wood, fabrics, and causes colors to fade.
Infrared light is basically heat. Low E glass has the ability to allow visible light to pass while blocking certain amounts of UV light and IR light.
The infrared light in sunlight is powerful. When it strikes an object it heats it up. These objects can be your tile floors, furniture, sidewalks, patio furniture, etc. As these objects cool off, they emit a low powered form of IR light. Low E glass reflects this form of energy. In the summer this helps to keep your house cooler, as the heat from objects outside is kept outside. In the winter, all objects in your home are heated (by either the sun or your furnace). This heat is also bounced back into your house by the low E glass.
There are two types of low E glass: hard coat and soft coat. Tin is applied directly to the molten glass to make hard coat low E glass. It is hard to scratch the tin off the glass. The soft coat process commonly involves the application of a thin layer of silver while the glass is in a vacuum. This coating is delicate. Soft coat low E glass is always sandwiched with another piece of glass. It can also oxidize if exposed to air. Argon gas is sometimes used to prevent this oxidation. This gas also acts as an additional insulator.
Low E glass helps to reduce condensation on glass. The inside surface temperature of the glass is warmer. The differences can be dramatic. Imagine a cold night with an outside temperature of 0 degrees and a 15 mph wind. The inside temperature of a single pane window would be approximately 26 degrees. Regular double pane glass might register 35 degrees. Hard coat low E glass would be very near 49 degrees. And weighing in at champ would be soft coat low E glass at 62 degrees.
Some glass manufacturers have gone even farther. They have suspended thin, low E transparent films in between pieces of glass. This system has excellent performance characteristics. Some of these films can block 99.5 percent of UV light. Some boast an insulating value twice that of soft coat low E glass.
Low E glass is worth the price, especially since houses tend to lose 25 percent of their heat through windows. Purchase the highest quality low-E glass you can afford.
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Comments:
Myron 01 Jan 2008, 17:21
AsktheBuilder 01 Jan 2008, 19:05
Myron,
You need to ask this question to a physics scientist.
todd 02 Jan 2008, 06:10
Myron,
Yes low-e coatings are directional and for optimal control over radiative heat transfer need to be ordered & installed accordingly. In my house, "solar control" windows are the best choice for the east- and west-facing windows (the afternoon summertime sun just slams the west face of our house with unwanted radiation) and then "cool climate" orientation for north and south faces.
Joe 18 Jan 2008, 15:03
Low E is a wonderful product but it doesn't last the life of the window.
Basicly the first generation was a "sputter" coat or spay painted as it was
on. This will last only 5-6 years before the UV rays break it down and it
will start to flake to the bottom of your window. When you see a rainbow
effect at the top of your window, then you know the Low E has failed and is
no longer effective. The Second generation was baked into the glass and
then the sputter coat was added. The problem is is that when the Low E is
baked into the glass it groups together, think of it like a cookie with
chips in it. The chips representing what happens to the Low E when it is
baked. And then the sputter coat fails and you're back to having nothing.
So why get Low E then? Don't, look for the newest technology called
thermalperm-E.
AsktheBuilder 18 Jan 2008, 15:12
Joe,
You had to know I would respond to a comment like this one. We need you to back up your statements with facts. Please point us to citations in the literature where glass scientists state what you have said above. Also, your last sentence makes me wonder out loud if you have a dog in this fight. Can you tell us if you are associated in any way to the new technology you mention? I simply can't imagine why you would take the time to comment if you didn't stand to gain in some fashion.
Don 28 Jan 2008, 08:01
Joe, We have 4 large (4' x 6')single pane windows in our living that face
north. Our problem is condensation on the inside in the winter. Will low
e glass help stop the condensation ?
AsktheBuilder 28 Jan 2008, 11:11
Don,
Low-E glass will not stop condensation. I just wrote a New column titled Window Condensation. It will be loaded to the website late in the day January 28, 2008. Look for it in the Condensation category. You can get email updates each time I load all new columns and videos. Look way at the top of this page for the Subscribe button.
Dan Davies 16 Feb 2008, 11:58
OK I'm confused. When I designed and built this house 20 years ago I
oriented the house to face south with a vast window array to take advantage
of the solar gain in the winter time. The morning sun streaming in quickly
warms the house and causes the heater to shut down. I love the warm morning
sun! In the summer the windows are in the shade so have no direct gain.
Now, I'm looking at upgrading my windows. I don't want to lose my "solar
gain" in the winter time but also realize that I will have less heat loss
at night. I currently use blinds to accomplish this. I will put low e
windows on the east, west, and north sides. Will switching to low e on the
south side help or hurt my current situation? How can I calculate this? I
know there are many factors to consider...climate for instance. I'm on the
central coast of CA but inland w' probably 60-80 nights slightly below
freezing/year. This is a big investment and I want to do it right! Help!
Dan
AsktheBuilder 16 Feb 2008, 12:38
Dan,
Read all of my Low-E Glass columns. There are two types of infrared...... Discover which one Low-E reflects in my articles.
Kurt 01 Mar 2008, 17:15
Joe is wrong (which is why he never posted data to back it up). Hard e-coat
cannot physically detach.
> A hard e-coat is a pyrolytic coating applied on-line during the initial float glass manufacturing process. Since the coating is applied while the glass is still in a semi-molten state, it becomes part of the glass. Also, a correction to article above. All float glass has tin on it - tin is not the low-e coating. >Float glass is produced by floating molten glass on molten tin. The surface of the glass that contacts the tin ("tin surface") acquires a very small amount of tin. Dan, In warm climates, class with a low shading coefficient or low solar heat gain coefficient is preferred. For cold climates, higher is better. View all comments |
