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Energy Efficient Windows

If you are planning to incorporate solar passive applications in your new home plans energy efficient windows will become an important consideration.  Replacing windows on existing dwellings could boost your energy efficiency, also, they are not just for new projects.  Windows today are much more efficient than they were ten years ago, so replacing existing ones could have a large impact on your utility bills.

A solar passive home makes the best use of the sun for light and heat.  Choosing the right windows is critical for getting the best possible results from this type of home design.  Today's windows are designed for different orientations in your home.  Some are designed to keep heat out and some lend themselves to allowing more heat in.  Other factors to consider when deciding on windows are the views you want to enjoy, your need and desire for natural lighting and the possible effects of this light on your furniture.

When shopping for energy efficient windows you will be looking at a lot of acronyms and numbers.  Let's take a look at some of them and learn a little about what to look for when buying windows for your home.

• Visible Transmittance (VT) - This number, between 0-1, states how much light comes through a window.  For passive solar uses this number should be high.
• U-factor rating of the National Fenestration Rating Council (NFRC) - the lower the number, the more energy efficient the window, based on the glass, frame and spacer material.
• Low-e (low emissivity) - A thin, invisible coating on the glass controls the amount of heat moving through it in both directions, in and out.  This affects the U-factor and the SHGC.  Low-e windows can save save you up to 50% on your utility bills.
• Solar Heat Gain Coefficient (SHGC) - This figure lets you know how much heat a window transmits.  For passive solar gain, this number should be higher than .6.  For windows on the north side that let sun in during the summer, this number should be lower to block the heat.

For passive solar applications you want A high SHGC, a low U-factor, a high VT and Low-e windows.  For your northern orientation windows you are looking for a low SHGC, a high U-factor, a low VT and Low-e windows.

It will probably cost a little more to buy high quality energy efficient windows but this is not the place you want to skimp by buying inferior or off brand windows.  Start with a reputable dealer, look at brand name windows and then further research them on their websites.

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