What is R-Value and U-factor?

It is rare to find someone who is knowledgeable on R-value and U-factor outside of the window industry. But the truth is, these are important concepts to know and understand when deciding which windows are going to be the best for your home. These two words will tell you how well your windows work, and if you are getting your money’s worth on your windows. We will briefly describe what these words mean and how they are associated with getting the most value out of your windows.

U-Factor

The U-factor is the measure of heat transfer through 1 square foot of material. This measurement is used to measure both heat gain and heat loss through the glass. The number is based on specific material property value and is an indicator of heat resistance. It also is an indicator of energy efficiency and measures insulation abilities. Essentially what U-factor measures is how well a windows prevents heat from escaping a home or building. It is measured numerically, and a lower number means that the window is better at reducing the transfer of heat. This means that it is better at insulating a room or building compared to windows that have a higher U-Factor. While it’s important during all months of the year, having windows with a low U-factor is most important during the winter. This is because during the cold winter months, you want to make sure as little heat as possible is escaping through the windows. Not only will this keep you warmer, it is also going to cost you less to keep your home at an ideal temperature during the winter. Overall, U-factor is extremely important when it comes determining how your windows will affect the climate inside the home.

R-Value

R-Value is another important metric when determining how effective a window is. While U-factor is the measurement of heat transfer, R-value is a measurement of a materials resistance to heat flow. So it is the rate at which heat is transferred or lost based on conduction and resistance of heat transfer. In simpler words, it’s how well heat can transfer from the inside out or from the outside in. While this may sound a lot like U-factor, it should be noted that R-value strictly refers to the glass aspect of the window. The U-factor refers to the window as a whole, including it’s frame.

A high R-Value indicates that the window has better insulation and resistance to heat transference. The importance of this number is that less heat is going to come through the window, especially during the summer. If the window has a high R-value, then when the sun is beating on it, less of that heat is going to be transferred through the window. Windows with a very high R-value can actually block out 99%+ of UV rays and heat transference. This means that all of the light will still be able to enter the room, but none of the harmful UV rays and the heat that usually comes along with it. In recent years, Heat Mirror Technology, has done a successful job in insulating windows in this way. Windows fitted with this technology use a thin Krypton insulated film that deflects harmful UV rays but still allows in sunlight. Windows with this technology have been featured on the Empire State building and have been known to save them money each year on their energy bill.

The Bottom Line…

There are quite a few possibilities out there when it comes to finding windows that have both a low U-factor score and a high R-value. Finding these windows is important if you are looking to get the most out of your windows, as well as saving money in the long run. These two numbers will show how well your windows insulate your home, and how well they stop the transfer of heat. If you are looking for windows that have good scores in both respective categories, here is one window that we recommend.

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