What is U-value of Windows?

U-Value: The U-value (or thermal transmittance) is a measure of how well a window prevents heat from escaping. It is influenced by the insulating properties of the gases trapped between the glass panes in double or triple glazed units. The lower the U-value, the better the insulation. Measuring and optimizing the U-value is essential for improving energy efficiency in windows and therefore in buildings. Check NFRC label to see how they present this information.

How is gas concentration related to u-value?

In the context of insulating glass units (IGUs) and their gas-filled spaces, the concentration of insulating gases (such as argon or krypton) is directly related to the U-value of windows. The U-value is influenced by the thermal conductivity of the materials and the air or gas within the IGU.

Insulating gases have lower thermal conductivity compared to air. This means that they are less effective at conducting heat. When the space between the glass panes in an IGU is filled with an insulating gas, it reduces the overall thermal conductivity of the unit. Lower thermal conductivity translates to a lower U-value which is what is looked for.

There is an optimal concentration of insulating gas that maximizes the reduction in thermal conductivity. Beyond this optimal level, the additional benefit in terms of U-value reduction diminishes. Therefore, it’s essential to have the correct gas fill concentration by measuring gas level of IGUs to achieve the desired thermal performance. Read what is the optimal gas fill rate.