There is a certain amount of anxiety that takes hold when walking through a store like Home Depot or Lowe’s.

First there is the notion that perhaps by even purchasing something there you are forsaking your eco-friendly, sustainable ideals. Then there is the thought that perhaps if you held out long enough and scoured carefully enough you would find the same item at a second-hand supply store or on Craigslist or at a liquidator. And lastly there is the feeling that while you are willing to purchase a new product (even despite its carbon footprint that will surely cause you to lose sleep over) you have very little clue as to whether it is a wise purchase for your needs anyhow. Such is the case recently when parusing the window aisles at our local builder box.

It is a given that as a tiny houser one knows that windows are vital to the overall aesthetic of the house as well as the energy consumption. But how? We have already talked about different styles of windows but within each of those styles there is a contractor hieroglyphic that is known by few. It involved letters and numbers and codes and You probably already know that if you are building a new home or remodeling your current one, the windows that you choose will significantly affect the overall look. What you may not know is that they will also affect how energy-efficient your home is. However, it can be difficult to know what the difference is between the R-value and the U-factor. And what about all of those windows that claim to be low-E? It’s time to clear up all of the confusion!

  1. R-value.  This is the biggest factor in the energy efficiency of your windows.  But the real question is – what in the world is R-value and how does it affect your windows?  To put it simply, R-value is the measure of how much heat loss your windows are capable of preventing.  Therefore, you want windows with the highest R-value possible.  The lowest R-value that is acceptable if you are trying to build an efficient home is R-3.  Of course, the higher the rating, the more efficient the window.  The corollary to that is the higher the R-value, the more expensive the window will be.  A good rule of thumb is to choose a window with the highest R-value that you can reasonably afford, in relation to the energy savings that you expect to receive.  This is especially true if you live in a cold climate.  Keep in mind that R-value is rated according to the window’s efficiency in the center of the glass.  The edges will be less energy-efficient than the R-value reflects.
  2. U-factor. This is the second big factor to consider when choosing your house windows.  U-factor is the measure of how well your window prevents air leaks between the sash and the frame.  U-factors less than 0.35 are considered energy efficient.  If you live in a climate that is cold and windy, you’ll want to give just as much weight to the U-factor of your windows as the R-value.  You may also want to consider insulation of some sort for the area in between our pane and your sash.
  3. Low-E windows. This type of window is considered the gold standard when it comes to energy-efficient windows.  Introduced in 1979, Low-E (also known as low emissivity) windows consist of an inner and outer pane of glass and works by reflecting heat back to its source by utilizing an ultra thin metallic coating on or in the glass. The area between the two panes is also filled with an inert (non-active) gas such as argon, which provides the ultimate in window insulation without compromising the clarity of the glass.  A step down from low-E windows are single-glazed and double-glazed windows, which are coated with a transparent metallic oxide finish that prevents some heat loss.  These are much less efficient than low-E windows, which is also reflected in their lower R-values.