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Sunset Air Blog

Understanding the Heat Efficiency Numbers for Windows

A window is more than glass or other transparent material in a frame. A window forms a part of the energy system in your home, and the right selection and placement of new windows can make a difference in how well your home is heated and cooled.

A key part of understanding the role of windows in energy efficiency is knowing how to read the energy-performance labels from the National Fenestration Rating Council, a nonprofit industry-recognized certifying body for windows and doors. NFRC labels appear on all windows that have met the council’s standards, and contain a list of efficiency numbers. There is also an ENERGY STAR label from the U.S. Department of Energy that identifies the climate for which the window is certified.

If this already sounds like it’s too complicated, you don’t need to worry: if you hire experience professionals for your new window installation, they will guide you toward the energy-efficient window for your construction project that will reduce your costs for heating and cooling. Sunset Air offers quality window services in Lakewood, WA that combine experience and professionalism to make sure that you receive precision window installation.

The Efficiency Numbers to Look For

  • U-factor: This is the measure of the heat loss through a window. The lower the number, the more the window inhibits heat flow and the higher its insulating ability. Generally, the U-factor for a window will be between 0.2 and 1.2.
  • Solar heat gain coefficient: The SHGC indicates how well the window blocks radiant heat; i.e. the heat produced from direct sunlight on the window. The SHGC number is the fraction of the radiant solar energy that passes through the window. It is expressed as a number between 0 and 1, and the lower the fraction, the better the window restricts heat.
  • Visible transmittance: The amount of visible light that enters the window. Like SHGC, it is measures from 0 to 1. The higher the number, the more visible light enters your home.
  • Air leakage: A measure of the cubic feet of air that passes through a window per square foot of window area. The lower this number, the less air will escape through the window. Keep in mind that poor installation will increase air escape, so the air leakage number is only meaningful with skilled installation.
  • Condensation resistance: This rating expresses how well the window stops the development of condensation formation on its interior surface. The higher the number (expressed between 0 and 100), the better the window is at preventing condensation.

Your professional window installers will help you with each of this efficiency numbers, and they will know the ratings that a window must score for NFRC certification. They also will identify the proper ENERGY STAR windows for your climate. Best of all, the professionals will make sure that the window is set and sealed into place so that it can live up to its efficiency numbers and do the job it is supposed to.

Since 1976, Sunset Air has helped homeowners with in Lakewood, WA with window services, door and skylight installation, and other home improvements. For all your window needs, contact our team.

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