These two letters are very important when it comes to judging the quality of a replacement window. Both measure something different.
In a nutshell, U-value tells you how well an IGU, or insulated glass unit, can hold in hot or cooled air, while R-value measures the capacity of the window to resist heat flow. It may sound a bit confusing, but lower U-values show a better insulating performance, and higher R-values show better thermal resistance. When purchasing replacement windows, knowing the difference between U-value and R-value will help you choose the most energy-efficient windows.
Similarities and Differences
What do both U-values and R-values have in common? They both measure energy efficiency. Now for the differences:
- U-value, or U-factor, measures heat transfer (heat gain or loss through the glass); R-value measures heat resistance. U-value is not a rating for material; rather it calculates the conduction properties of a variety of materials used to make windows, doors or skylights.
- R-value measures how well a specific material performs, such as insulation, based on how well it can reduce the transfer of heat.
- U-values show how well an insulated glass unit (IGU) can hold in hot or cooled air. The lower that number, the better it insulates. This value will range from 0.1 (or very little heat loss) to 1.0 (very high heat loss). You measure the U-value of a window by the number of British thermal units, or BTUs, that go through each square foot of area/degree of temperature difference from one side to the other.
- In calculating R-value, you divide 1 by the U-value figure. In calculating U-value, divide 1 by the R-value.
U-value and R-value are basically mathematical reciprocals of one other. So while a lower U-value indicates better insulating performance, a higher R-value indicates better thermal resistance.
A Closer Look at U-Value
U-value, a scientific calculation that measures the rate of heat flow through one square foot of material, measures how well a particular product can prevent heat from escaping a home. The lower the U-factor of a window, the better it’s able to reduce heat transfer. In other words, the less heat that could be lost. The U-factor refers how energy efficient the whole window assembly is, which is particularly important during winter.
A Closer Look at R-Value
R-value is a material property value, responsible for measuring the material’s resistance to heat flow. This is especially critical in the rating of insulation in your attic, but also applies to windows. R-value measures the rate of heat transfer or loss, based on resistance and conduction. A high R-value indicates the product insulates better and resists heat transference better.
Contact Allstar Construction and Maintenance for Condominium Window Replacement
Here at Allstar, we have many years of experience installing replacement windows of varying U-values and R-values. We would be happy to let you know more about each value and what your chosen window is rated. To learn more, contact us today at (952) 234-9995.