What is the U-Factor on Replacement Windows?

If you have been looking at replacement windows in Newberg, OR you may have heard a window dealer mention the R-value or the U-factor. Both are used to measure energy efficiency, but not in the same way. These terms can be particularly perplexing to homeowners, and you are not alone if you aren’t sure what they mean. So here is some information that can help you sort out the differences and use these references to help you select the right products for your home.

What is the R-Value?

The R-value was originally developed to measure the thermal performance of insulation. Now it is used to define the efficiency of different building materials. Materials with higher R-values have more resistance to heat flow, which equates to better insulation. But because the R-value is used for specific materials or just a certain component, it hasn’t been used often when it comes to window assemblies. Instead, the National Fenestration Rating Council (NFRC) uses the U-value on energy labels to rate replacement windows.

What is the U-Value or U-Factor?

The U-value measures the rate of heat flows through one square foot of material. In basic terms, the U-value is often seen as the mathematical reciprocal or inverse of the R-value. So 1/R=U. And as the R-value goes up, the U-value goes down. But it is actually more complex. The U-value designates the thermal performance of a system instead of just a homogenous material. It accounts for both conduction and radiation, how energy both enters and leaves the material. It also takes into consideration convection or airflow around the window. A lower U-factor for the whole window means better energy performance. So a U-factor of 0.05 is better than a U-factor of 0.09.

What if the Window has an R-Value and U-Value?

While U-value still remains the industry standard, recently more window manufacturers have started including an R-value for labeling their products. This is because it is easier for consumers to understand that an R6 product has better energy performance than an R5, rather than comparing a 0.15 product to a 0.2 product. That said, the R-value still defines the efficiency of a specific component, like the window frame or the glazing. It is a good place to start, but you should still consider the other ratings on the energy labels. On the NRFC energy labels, you will be able to see a U-factor for the entire assembly instead of just a single component. It will be a better measurement to use when comparing products for energy efficiency. You will also be able to use the Solar Heat Gains Coefficient (SHGC), and Visible Transmittance (VT) to compare products.

If you need help navigating the energy labels on replacement windows in Newberg, OR contact EnergyGuard Windows & Doors. Our experts can answer any questions you might have about R-values, U-factors and any of the other ratings on NFRC energy labels. They can also help you find the right combination of materials and technologies to get the type of energy performance you want.