Home Improvement Blog: A Toolbox of Ideas

Energy Efficient Windows - What Are They Made Of?

Posted on Sun, Feb 13, 2011

So you are in the market for energy efficient replacement windows because the ones you have might be old aluminum, warped wood or just down right drafty. In recent years the craze has been about the energy efficient window with the Energy Star Rating. But you ask yourself, “What exactly is an energy efficient window and what are the components that make it up?”


Energy Efficient Window RecipeYou can look at it as if you were looking for that perfect recipe for that “perfect chocolate cake”; just enough flour, sugar, cocoa and the right amount of baking soda so it doesn’t come out of the oven flat.




Here is what to look for in the Energy Efficient Window Recipe:


LoE Glass:

LoE means low emissivity and it’s the term used to describe a special microscopic coating on the panes of glass.  Recently LoE3 (pronounced “Low E Cubed”; actually has three coatings of LoE on one pane of glass) was a major advancement in glass technology.  LoE is actually a layer of sputter coated silver that from the orientation that it is applied reflects the light.  The glass coating is also called “smart glass” because it keeps the majority of the UV rays out (non-visible to the human eye) and allows the good sunlight in (visible light). Check to make sure the window that you are considering has an energy star rating and the correct LoE coating for your climate.


Energy Star Rating:Energy Efficient Windows

The Department of Energy designed the Energy Star Program with the Environmental Protection Agency in compliance with manufacturers.  The windows must be tested by a certified independent laboratory and meet predetermined performance ratings to bear the Energy Star logo.  When choosing an Energy Star product, it will help reduce your energy costs and heating bills.


Weather Stripping:

Every operating window must be created in multiple frames to be operational.  Weather stripping is a key component to make sure that the seal between these frames is energy efficient.  Weather stripping must also be able to sliding sash of a window or be able to become compressed as in a casement window.  Bad weather stripping that does not seal correctly can make what could be a great window into a terrible, inefficient one. There are many forms of weather stripping in windows to make them air tight.  Types of weather stripping include, but are not limited to: foam reinforced, felt, vinyl tension seals, closed cell foam tape, gaskets, sweeps, bulb seals, and more.  Some companies even have a magnetic weather stripping to vacuum seal the window shut.  Weather stripping when used correctly will help reduce air infiltration and can be a major factor in the energy efficiency of a window. 


Efficient Frames:

The material used for the main and sash frames of a window is also very important.  The most energy efficient materials used commonly today are wood, vinyl and fiberglass.  Each material has its pros and cons.   Vinyl is the most common of the three due to its thermal properties, lower maintenance and lower cost for the same performance ratings.  Vinyl Energy Efficient WindowA vinyl frame or sash that is insulated with foam filled insulation will help make your window more energy efficient. Most vinyl windows need to be reinforced at meeting rails as in the middle of a double hung.  Most windows use metal reinforcements, but some manufacturers use new composite reinforcements for the highest possible ratings.  Vinyl windows with a fusion welded corner (versus a conventional corner just screwed together) will not allow cold air to enter through the window frame corners because the vinyl “fuses” to itself eliminating any potential leaks.   When a corner is screwed together, the corner is not perfect and will not be as efficient.  When considering replacement windows, vinyl and wood have very low conducting qualities making them great choices for frame materials.  On the other hand, metal aluminum windows have high conducting values making them poor choices for most applications. 


Argon Gas:

With energy efficient windows, the glass is usually the least efficient component.  But when purchasing windows it is usually the reason why you are buying windows because of the glass and the view it will give outside of your home.  Energy efficient windows feature special insulating glass for optimal energy efficient.  Each window’s insulating glass unit is comprised of multiple panes of glass, a spacer system between the panes, LoE coating(s) on the pane(s) of glass, a spacer system to bond the panes of glass and gas sealed between the panes.  The gas inside of the insulating glass unit is commonly overlooked but it actually a critical component of an energy efficient window.  When special “heavy” gases are captured in between the panes, the rate of energy conduction and convection is minimized.  In simple terms, the heavier than air gases have much larger molecules making everything inside of the glass move much, much slower than air.  So, heat transfer is basically minimized between the panes of glass.  Argon gas is the most commonly used gas because it is non-toxic, nonreactive, clear and relatively inexpensive.  Krypton glass is also used, but is very expensive to produce and only typically used for very small air gaps.  Argon gas is a component that every energy efficient window should have.


ChocolateCakeSliceSo, at the end of the day, did your cake rise to the perfect height and after the frosting was spread, was it delicious?





Or, once you chose your energy efficient replacement windows and after installation, did they meet your expectations and save you on your energy bills?  Let us know.


Thinking about windows for your home?  Make sure you download the free window guide!

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 Photo Credits: Chocolate Cake; Cake Slice


Tags: Energy Efficiency, Replacement Windows