How to Use R-Values and U-Values in Casement Windows How to Use R-Values and U-Values in Casement Windows

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This How-To Guide

A casement window is a window attached by hinges on a frame. The hinges allow the window to open. When considering a new casement window, it is important to understand the insulating values.  These values are know as the R-value and the U-value. Below are some guidelines for how to use R-Values and U-Values in casement windows.

Step 1 - Understand the Definitions

The R-value is the measure of the thermal resistance. The larger the R-value, the better the effectiveness of its insulating properties.  

The U-value is how well it conducts heat. The smaller the U-value, the better the effectiveness.

Step 2 - Understanding the Meaning of the Values

A high R-value rated window will lose less heat than a low R-value rated window. Windows are usually rated by their R-values and not their U values, but, if you see U-values, it will be the opposite of the R value. If you remember that the higher the R-value, the better the insulator and that U-values are the exact opposite, you should be able to compare different windows.

Step 3 - Understand Features Influencing the Values

  • The glass in a window can have a single or multiple layers. The more layers, the better the insulating factor, so therefore, the higher the R-value. Also, the air space gap between layers will come into play in multi-layered windows.
    The glass itself is a determining factor: treated glass vs. plain glass vs. plastic. Some plastic manufacturers claim that their product can add to the R-value over untreated glass. A dual-glazed window will have twice the value as a single-glazed window.  There are even different types of glazing. Analyze each window on its total merits. 
  • The material which makes up the window frame will have different insulating factors. Wood is an excellent insulator and better than steel. You need to weigh all the window properties together. The R-value listed on the window will be the total thermal resistance of the window.
  • How well the window is installed is a great determinant of the insulation. A window with a very high R-value will be ineffective if there are gaps allowing air to enter. Be sure all cracks are sealed. Use expandable foam for large areas and plenty of caulking for smaller areas and always caulk around the installation both inside and out.

Step 4 - Understand the Difference of Geographic Location

Different areas of the country will have different recommended R-values. It is best to do a little research and see what is suggested. You may live in a climate where a lower R-value will be just as effective as a higher one. This could give you further alternatives to the window composition and style you purchase.

Step 5 - Understand Energy Star Label

The Energy Star label is an indication of a highly efficient product. Look for the label when shopping to be sure you are purchasing a good product because this will indicate that you are purchasing a product with good thermal resistance.

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