Selecting the correct window is important for energy efficiency, as well as comfort, and your specific climate is a major variable to consider. A window that keeps out the heat in the summer may not keep out the cold in the winter and visa versa. If you are building a new home, remodeling or just considering new windows, you need to arm yourself with some knowledge before talking to your builder or window professional.
When looking at windows you will notice energy rating labels to help you compare energy-efficiency of various windows. The ratings and labels are created by a nonprofit council operating a voluntary certification program. This program catalogs heat loss and gain using U-factors and SHGC (Solar Heat Gain Coefficient). There are additional ratings, but to avoid being overwhelmed, let’s start with understanding these two systems.
- U-factor indicates the amount of heat lost through a window with values between .25 and 1.25. The lower the U-factor, the better the window insulates. U-factor is especially important in colder climates where the temperatures inside versus outside are greatly different.
- SHGC represents the ability of insulated glass to reflect solar radiation from the sun. Simply put, it tells you how well the window blocks heat caused by sunlight. This is represented by a number between 0 and 1. The lower the number the more resistant it is to solar radiation (the less solar heat the window transmits). Northern climates it is best to have a high SHGC while Southern climates it needs to be a low SHGC number because you want less solar radiation to penetrate.
So, how do you select a window for Mixed Climates like we have here in the Ozarks?
As a guideline, look for windows with a U-factor less than or equal to .40 for less heat to be transmitted and a SHGC of less than or equal to .40 to reduce air conditioning cost and improve comfort. Energy Star recommends a U-factor equal to or less than .40 and SHGC equal to or less than .30. The direction your window is facing (North, South, East or West) is an additional factor you need to consider before your windows are installed. Ask your home builder or remodeler to advice on your window selection. A good builder or remodeler wants you to be comfortable and prefers that you save money in the long term.
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