If you’ve been shopping for new windows any time lately, you may have heard a lot of buzz about the U-factor. You may wonder why it’s so important. Well, we are here to explain everything. In a nutshell, it’s a measurement of how energy efficient the window is.
Energy Star defines U-factor as the measurement of the rate of heat transfer, with this rating telling consumers how well the window insulates. Ranging from 0.25 to 1.25, U-factor is measured in Btu/hr-ft2-oF. As a result, you can use this energy performance ratings of windows (as well as doors and skylights) to inform you of their potential for gaining and losing heat, or transmitting sunlight into your home.
The National Fenestration Rating Council (NFRC) is the entity that provides testing, certification, and labeling of windows and related products based on how well they perform in terms of energy efficiency. When you spot the NFRC label, you can rest easy knowing the window has been sufficiently rated based on its energy properties. This also helps you to better compare products when shopping for windows.
Keep in mind that the NFRC is the industry-recognized certifying body for windows, reporting raw numbers only. It’s the U.S. Department of Energy that determines those numbers and slaps an Energy Star label on the ones its deems superior in terms of performance. It also pinpoints the climate zones for which the product is certified, adding its seal of approval on those products that meet its high standards.
All About Heat Gain and Loss
Basically, the lower the U-factor, the more energy efficient the window is. Put another way, the lower the U-factor, the greater its resistance to heat flow and the more reliable its insulating properties.
Your windows can gain and lose heat in many ways, such as through:
- Direct conduction through glass.
- Via radiation from the sun into a house and out of the house, such as from room-temperature objects like walls, people and sofas.
- Air leakage.
When considering U-factor, remember that this is the rate at which the window conducts heat flow that is not related to solar. It may refer to the glass alone, but most times, as with NFRC U-factor ratings, they refer to the whole window performance, including spacer materials and frames.
Double pane, high performing windows may have U-factors of 0.30 or lower, while some triple-pane windows can have U-factors as little as 0.15, according to the Efficient Windows Collaborative.
It’s important to have a trusted window installer on your side to help you make sense of which windows have the best U-factors. Rescom Exteriors only installs replacement windows that carry the NFRC label, ensuring that our clients receive the very best in energy efficient windows. To learn more, call us at 508-832-5202.