Every replacement window comes with an energy rating label from the National Fenestration Ratings Council (NFRC), an independent testing laboratory that measure the performance of windows and doors. (“Fenestration” means “opening.”) In fact, the state of Massachusetts requires that it be visible on any window presented for sale.
Among the most important measurements when it comes to energy efficiency is the U-factor of a window. In order to make an informed decision when buying replacement windows for your home, you should have an understanding of this rating.
You may be familiar with a measurement called “R-factor” for insulation. This is a rating given to insulation in walls and ceilings. The biggest difference between U-factor and R-value is that U-factor measures the rate of heat transfer (or loss) while R-value measures the resistance to heat loss.
R-value is a measure of conductivity. A product with high conductivity will transfer heat quickly, like a hot pan on the stove or a single pane of glass on a cold day.
U-factor, on the other hand, takes into account more than conductivity. It also is affected by the airflow around the window and the emissivity of the glass. Emissivity is the ability of a product to absorb certain types of energy (specifically infrared) and radiate that energy through itself and out of a room.
A product with high emissivity, such as one pane of clear glass, will transfer over 84 percent of the infrared energy from a warm room outside to the cold air. The lower the conductivity and emissivity of the glass, the lower the rate of heat loss and the lower the U-factor.
There have been significant technological developments over the last 10 years involving low emissivity (low-e) coatings on the glass. There are now many glass products available with these low-e coatings, which are typically used in dual pane windows and insulating glass units.
The key, then, is to look for a window with a low U-factor rating, showing that the window has low emissivity.
Look for the NFRC label on all of our replacement windows. It shows that the Bristol replacement windows we install have among the lowest “U-Factor” of all windows tested by the NFRC. The lower the U-value, the greater a window’s resistance to heat flow and the better its insulating value. That means Rescom’s windows are among the best for energy efficiency, keeping you warmer in winter and cooler in summer.
For more information about upgrading your windows with energy efficient replacement windows from Rescom, call us toll-free at (866) 410-5884. Or visit our web site at www.iwantnewwindows.com.