Selecting new windows for your home can be a daunting process. There are many factors to consider as you shop for replacement windows. As you look around at various windows, you may notice different terms on the stickers adhered to them with different numbers next to these terms. These terms are important to the function of the window, and the numbers next to them represent how efficient it is at that particular task. Familiarizing yourself with what these terms mean, and what a good number is for that task, will help you select a window that meets your needs. Here are four terms you should be familiar with as you shop for new windows.

Air Leakage

Air leakage is listed as an AL rating. This refers to the amount of air that leaks in or out through cracks in the window's assembly. Ideally, no air would leak in or out, but unfortunately, that isn't the case. There are always tiny spaces and gaps in the window frame and casement that allow this to occur. The lower the AL rating, the more efficient the window is at preventing air leakage. This is an important factor to consider, as your energy bill can increase if large amounts of air are exiting or entering your home.

In order for a window to receive an Energy Star rating, it must have an AL rating of 0.30 or below. As such, you should look for this rating to find the windows that are most efficient at preventing air leakage.

Condensation Resistance

Condensation resistance, listed on windows as a CR rating, measures how well one resists moisture forming inside. Condensation can cause structural damage to the wood framing around your window. And if you have double pane glass, the moisture can get stuck inside, causing your windows to look foggy. A CR rating can be anywhere from 15 to 72. The higher the number, the better the window is at preventing condensation from forming. The lower the number, the more likely it is that moisture will form.

It is important to note that this is not a required rating and will not be listed on all windows. It is up to the manufacturer as to whether they want to list their CR rating.

Solar Heat Gain Coefficient

The solar heat gain coefficient is listed on a replacement window sticker as SHGC. The solar heat gain coefficient refers to the ability of the window to control sunlight from entering and causing your home to heat up. The amount of sunlight that can get through is typically controlled by glazing techniques. The SHGC is listed on the sticker as a number from 0 to 1. The lower the number, the better the window is at preventing your home from heating up due to sunlight. The higher the number, the less effective it is at controlling heat gain from the sun.

Once again, this number is not required to be listed on windows, though most companies do list it. The exception to this is windows rated Energy Star Efficient, which are required to list their SHGC rating.

Visible Transmittance

The last term you should be familiar with as you shop for replacement windows is visible transmittance, or VT. VT refers to how much visible light is transmitted through the window. VT has a rating of 0 to 1, with the most windows falling between 0.30 to 0.70. If you are looking for a lot of natural light in your home, you will want a higher VT rating. If you prefer to keep your home darker or want less natural light, you will want a window with a lower rating.

With so many different windows on the market, selecting the type that is ideal for you can be a big task. However, paying attention to performance factors, such as air leakage, condensation resistance, solar heat gain coefficient and visible transmittance will help you zero in on the windows that have the efficiency standards you desire in your new ones.