Energy Efficiency
You are looking for windows that will properly insulate your home in winter and summer, helping you to make the most out of your heating and cooling systems. This requires selecting windows and materials that have earned high industry ratings for their performance. There are several ratings to look at when you are considering your options. Understanding and utilizing these ratings will enable you to maximize the ability of your home to maintain a comfortable climate with peak efficiency.The U-Factor
One of the primary ratings to consider is the U-factor of a window. The U-Factor, simply put, measures the heat loss through the entire system of windows. The lower the U-Factor number, the high the ability of the window to insulate. So you want to find windows that have a low U-Factor. In addition to this factor, how you insulate your windows will also have a big impact on the energy-efficiency of your home. Using fiberglass to insulate is much more effective than an aluminum frame. Combine a low U-Factor window with a fiberglass or vinyl frame, and you have a smart, potent setup to keep your home comfortable.Another factor to consider is the R-Factor of a window. The R-Factor is the inverse of the U-Factor, so a higher number is better at indicating efficiency.
Social Radiation and Visible Light
No
matter what the outside temperature is, heat can enter a house through
direct or indirect solar radiation. How well a set windows controls
this heat gain is calculated through a measurement system called the
solar heat gain coefficient (SHGC) or shading coefficient (SC). The
SHGC rating on a window goes from 0 to 1. The lower the SHGC of a
window, the less solar heat it transmits, or allows to pass through. So
ideally you want to find windows with a SHGC as close to zero as
possible.You also want windows that transmit more visible light through, providing more daylight and reducing the need for electric lighting. This is measured by the VT, or visible transmittance, rating of a window. The VT is also measured on a scale of zero to one. Inverse to the rating of the SHGC (where a lower number, closer to zero is better), you want a VT rating as close to one as possible. This will mean that your windows allow as much sunlight as possible- but not as much solar radiation as possible! So you want to look for windows that have a high SHGC and a low VT.