How do Energy Efficient Windows Work?


Almost every homeowner is concerned these days with energy efficiency. The reason for such concern has to do with saving money. Energy efficiency translates into savings on utility bills each and every month. Over the course of a year even small monthly savings can add up to a fair amount of money saved.

One way that homeowners can save on utilities each month is to make certain that their windows are energy efficient.


Old-fashioned windows that allowed heat and air conditioning to escape quickly and easily are now a thing of the past. Today’s highly energy efficient windows are nothing like the windows of even twenty years ago. With older-style windows, a home could lose as much as 30% of its energy costs through its single-pane windows. In fact, windows used to be considered thermal holes, but no more. Today’s windows are closer to being thermal blankets than they are to being thermal holes.


How energy efficient windows work is not difficult to understand. Nor is it difficult to compute just how much the average homeowner can expect to save on utility bills each month.

High-efficiency windows consist of two or more panes of glass with an inert gas, generally argon, filling the space between the panes. This inert gas does not conduct either heat or cold well, thus providing an excellent thermal barrier. But that is not the only way an energy efficient window prevents heat from escaping a home.


  • When heat is lost by simply passing straight through an object and then escaping onto the other side of an object 10(such as heat passing through a single-pane window glass), this is known as conductivity.
  • Heat can also escape in other ways. It can pass through glass directly as infrared energy this is known as radiation.
  • It can also be lost through convection. When the warm air inside a home touches a cold pane of glass, the warm air gives up its energy, sinks to the floor and pulls more warm air against the cold glass, causing drafts.
  • The final way in which heat escapes is through poorly insulated areas as simple air leakage.


The speed with which heat dissipates has a U value. The lower the U rating, the better a material blocks the dissipation of heat. Insulation has an R rating. The higher the R-value, the better a material insulates.

Energy efficient windows sometimes have both an insulation rating (an R rating) and a U rating to indicate how quickly heat passes through the window. What the homeowner is looking for is a window with the highest R rating and the lowest U rating that is affordable. Many windows only have an R rating. Remember, the higher the R-value, the better.


Highly energy-efficient windows have a higher initial cost than normal windows, but initial cost is not the whole story.

Depending on weather conditions, high-efficiency windows can save the homeowner a quarter of their cost or even more in energy savings each year, meaning that high-efficiency windows can pay for themselves in four years or even less, and each year after that they are putting money into the homeowner’s pocket through utility savings.

With only a little maintenance, high-efficiency windows can last for fifteen to twenty years, or even longer, meaning that over their lifetime they pay for themselves over and over in energy savings.

Plus, as the price of energy continues to go up, the monthly savings grow even higher.


So how exactly does a high-efficiency window keep the sun’s heat out and keep the heat from the house in? Part of it has to do with the double panes and the argon gas as described earlier. However, a very large part of the “secret” of high efficiency windows is in the glass itself. There is an almost invisible coating on the high-efficiency glass. The coating contains tiny particles of metal, which reflect the sun’s damaging UV rays back outside the window to keep a home cool in the summer, and which also bounce the heat inside the home back into the interior of the house keeping the house snugly warm in the winter.


These windows, often called Low-E windows, in effect have an almost invisible mirror built into them that holds the home’s heat in and keeps the sun’s UV heat out.

An even higher R-value window has triple panes of glass, and two hollow chambers filled with argon gas. The 11primary problem with this type of window is the weight. Three panes of glass in a single window are heavy as well as bulky and require extra time and cost to mount properly. Such windows do, however, save a considerable amount of energy and so save the homeowner money on utility bills each and every month.

Possibly a better window yet has a sheet of a suspended film hung between two panes of coated glass. The suspended clear sheet is also coated with reflective metal particles just like the glass, but the suspended sheet is much lighter and slightly more transparent, allowing a clearer view than a heavier three-pane window while providing virtually the same high R-value of insulation. Suspended film windows are both lighter in weight and less costly.

The last element in energy-efficient windows are the low conductivity spacers mounted all the way around the edge of each piece of glass. The edges of glass represent the area most susceptible to the transfer of heat, but modern windows have placed low-conductivity spaces in this area to totally minimize the conduction of heat around the edges of the glass.

Thus an entire window system is created with one goal and only one goal: to keep harmful UV radiation out and to keep the good, clean heat of the building from escaping to the outside.



The result is a warm, comfortable living environment with utility costs kept to an absolute minimum. Homeowners considering replacing existing windows would do well to consider energy efficient windows and the long-term savings that they represent.

Those in the Northeast who are seriously looking at the monthly savings that high-efficiency windows provide should talk to the window experts at United Home Experts. The highly trained installers at UHE have years of training and real-world experience in installing high-efficiency windows and they can answer any questions that a homeowner may have including calculating how long it will take for the high-efficiency windows to pay for themselves in monthly utility savings.

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