“Blinds Between the Glass” refers to an innovative window system that features blinds or shades that are permanently sealed within a double-glazed cavity. Surprisingly, they have been around for a long time. According to Pella, one of America’s leading window manufacturers, they first introduced between-the-glass blinds in 1966. It’s only in the last few years, however, that they have surged in popularity to become a mainstream window option for homeowners who like a clean, modern look and the idea of minimal maintenance.
Companies that manufacture them cite their hygienic, maintenance-free convenience, their uniform and stylish good looks, and their innovative sun-shading and privacy features. As for homeowners with children or pets, their cordless design is a safety feature that is especially appealing. For allergy sufferers, eliminating dust-collecting draperies and airborn allergens seems like a pretty good incentive to purchase.
But are they energy efficient?In these days of soaring energy bills and dwindling resources, both personal and planetary, absolutely every homeowner is most concerned with energy efficiency when buying replacement doors or windows. It’s the one issue that probably trumps all others, because no one wants to see their hard-earned dollars vanish out the window.
So the question must be asked: Are blinds between the glass windows and doors really as energy-efficient as some claim? The only way to truly answer that question is to understand (a) what energy efficiency means in terms of windows and doors specifically and (b) how this type of window option is put together.
Window and Door Energy Efficiency 101
Modern windows are smart windows, and window science has completely changed how we understand energy efficiency. The measuring stick we use to gauge the energy efficiency of a window is sophisticated indeed.
We’ve known for some time that glass by itself is a poor insulator; however, double-paned windows created a revolution in the window marketplace. With double-paned windows, the two pieces of glass seal a layer of air between them, thus providing added insulation.
But there was another revolution in energy efficiency on the horizon, thanks to Low-E glass and argon gas. Low-E (low-emissivity) is a thin coating of transparent metallic material that’s applied to window glass for insulating purposes. The Low-E coating helps to prevent heat gain (or loss) in your home by acting as a kind of reflective shield, pushing radiant heat that tries to pass through the glass back to the source it originates from. Argon is a heavy, invisible, non-toxic gas that is a far better insulator than air-the weight of this gas dramatically reduces the amount of heat that can pass through the space between two panes of glass.
Today’s windows are in large part energy efficient because of the treated glass and the use of argon gas. Using stainless steel spacers for insulating performance and paying special attention to framing materials that permit only a low coefficient of thermal expansion so temperature variations don’t loosen the bond or create gaps are also important. But a Low-E coating is the critical element in making windows energy efficient.
How Do They Do That?
A popular TV ad asks, How do they get the caramel in the Caramilk bar? One could well ask the same question of blinds-between-the-glass windows and doors. How do they get the blinds in between the glass?
There are two ways in which these windows and doors are manufactured. First, many blinds-between-the-glass windows and doors are constructed like a glass “sandwich.” In other words, the blinds are inserted between two panes of glass. A Low-E coating is not applied, because silver oxide is especially sensitive to scratching. And there is minimal room in a glass sandwich with a blind for the maximum benefit of an argon gas fill. In comparison, there’s simply no way a window with between-the-glass blinds can reduce your energy bills as much as a sealed double-pane window.
The Triple Pane Option
With time, and in an effort to make windows with blinds between the glass more energy-efficient, some window companies turned them into triple-paned windows. That means they have three pieces of glass with two spaces in between: one space holds the between-the-glass blinds, while the other space has a Low-E coating and argon fill.
While triple-paned windows with blinds between the glass may be more energy efficient, just be aware that the extra piece of glass makes the windows bulkier. The biggest drawback to the triple-paned windows however is the cost. They are significantly more expensive because you’re basically paying for two windows-one with modern, energy-efficient technology, and one with between-the-glass blinds.
The Blinds Between: Innovation without the Science
One of the arguments put forth claims that the Low-E glass and the internal blinds together contribute to making the entire glass unit more energy efficient, that the internal blinds absorb solar heat gain. Let’s take a closer look at that claim.
There are no blinds-or window covering of any kind for that matter-that can significantly increase thermal efficiency and match that of a sealed glass unit with an argon gas fill and a Low-E coating. In fact, the blinds between the glass actually diminish the amount of argon gas you can put between those two pieces of glass, ultimately compromising the energy efficiency of the total package.
But most notable of all is this very simple fact: blinds, drapes, shades, and all other window coverings only marginally impact energy efficiency in one way: by blocking visible light transmission. In other words, sunlight! So even if your blinds are on the inside of the glass, it’s going to amount to the same heat reduction and light reduction that you would get from just pulling the drapes across or drawing a regular blind on a sunny day. You are simply blocking light, not increasing the actual energy efficiency of the window.
The Bottom Line
To sum up, this “augmented” energy efficiency derived from blinds between the glass is largely unfounded, and for two main reasons: internal blinds cannot absorb the solar heat gain and Low-E is absolutely essential for any sort of significant energy efficiency. It’s the only way to reflect radiant heat back to the source. Otherwise, heat transfers easily through the glass sandwich-blinds or no blinds. Inside or out!
You could save a lot of money and get equal or better energy performance from energy-efficient, double-paned windows with Low-E coatings and argon gas. But if you really love the look, then by all means go for it. Just know that your best energy efficiency option will be the triple pane solution.