There are many reasons you might need replacement windows on your home. The most important is fast becoming energy saving and cost reduction. Just be sure to do your homework first so you get the best value for your investment.

You may want to replace or upgrade the windows on your home for many reasons, but in today's environmentally charged climate, saving money (by saving energy) ranks at or near the top. It doesn't matter what type of windows are on your home now, newer replacement windows are likely far more efficient than those you currently have.

Newer windows are at a minimum double-paned (also known as double-glazed) and in some cases even triple-paned. Each space between windows provides for more insulation (because the trapped gas, usually argon, is a great insulator). It's much like layering your clothes on a cold Mid-Atlantic region wintry day. The more layers, the more trapped air, and hence, the warmer you feel.

Newer replacement windows also have better seals where the window frame is joined and when newly installed, come with improved sealing around the window and where it meets the wall of your home.

All of these act to lessen heat loss. But they also reduce noise and decrease condensation on your inside window pane. If condensation is or has been occurring around your windows, you will want to check for any water damage at the time you put in the replacement windows.

And, replacement windows can also give your home a whole new look. But it is the energy angle that really drives what most people think about when it comes to window replacement.

Most of us are familiar with R-values. These are how insulation and other components used to create the home's envelope are rated for resisting heat loss. But windows are different than insulation nestled between the walls. Windows let in light and allow us to see out. They interact with outside and inside air temperatures, sunlight and wind and they connect with us directly. Solar radiation (i.e., sunlight) also warms the windows and its framing even on cold winter days. This creates stresses that try to break the seals within and around the window.

As a result, the National Fenestration Rating Council (NFRC) has developed a system for uniformly rating window efficiency. Started in 1993, the system is used in the U.S. and elsewhere in the world.

There are 5 aspects to the rating system that you want to look for when choosing the best replacement windows.

The five factors are:

• (1) U-factor or ability to prevent heat loss from a home. This rating is usually most important in winter months and addresses the rate of heat loss. Values range from 0.20 to 1.20 and lower numbers are best.

• (2) Solar Heat Gain Coefficient describes how well the window works at blocking heat gain. Described in a range of 0 to 1, lower numbers are best.

• (3) Visible Transmittance tells how much light comes through a window. The higher the number (ranging between 0 and 1), the better the potential for daytime lighting.

• (4) Air Leakage measures air movement through a product. Here we are talking about the whole window unit, not just the window panes. Values range from 0.1 to 0.3. And lower numbers are best.

• (5) Condensation Resistance tells how well the product resists condensation on the inside of your window. Values range between 1 and 100, with higher numbers being better.

Be sure you don't just buy the least expensive replacement windows. You want your replacement windows to deliver long-term service for you and for anyone who may buy your home in the future. So, save the rating information and use it when marketing your home.

Do your homework comparing different brands of replacement windows and their ability to save you money. Then get a reliable installer, to get you started on realizing your return on your investment.