- Style. Some styles of windows are more energy-efficient than others. The most energy efficient ones are casement windows. These open from a hinge, either at the top or one side of the window, by means of a crank that you turn. Because the sash is designed to fit tightly against the weather seal when closed, they let very little air through. In fact, when the wind blows against the glass of a casement-type window, it pushes it against the sash, which simply makes it seal even more tightly. These usually fit in best with a contemporary design. The second type is the double hung window. This is the more traditional style with which you may be familiar. They consist of a lower pane and an upper pane. When you wish to open it, you slide the lower pane upward. The weather seal that is used on double hung windows becomes damaged over time, which means it lets in more air than an undamaged seal. However, these windows can usually be tilted inward for cleaning, which makes them more convenient in this aspect. The third type of is a sliding window. This is basically a double hung window, but it slides from left to right, instead of up and down. It is subject to the same sort of abuse as a double hung window, which makes it just as inefficient.
- R-value. This is the biggest factor in the energy efficiency. But the real question is - what in the world is R-value and how does it affect your windows? To put it simply, R-value is the measure of how much heat loss your windows are capable of preventing. Therefore, you want the highest R-value possible. The lowest R-value that is acceptable if you are trying to build an efficient home is R-3. Of course, the higher the rating, the more efficient the window. The corollary to that is the higher the R-value, the more expensive it will be. A good rule of thumb is to choose a window with the highest R-value that you can reasonably afford, in relation to the energy savings that you expect to receive. This is especially true if you live in a cold climate. Keep in mind that R-value is rated according to the window's efficiency in the center of the glass. The edges will be less energy-efficient than the R-value reflects.
- U-factor. This is the second big factor to consider. U-factor is the measure of how well your window prevents air leaks between the sash and the frame. U-factors less than 0.35 are considered energy efficient. If you live in a climate that is cold and windy, you'll want to give just as much weight to the U-factor of your windows as the R-value. You may also want to consider relocating to somewhere that's warm and sunny all year-round!
- Low-E windows. This type of window is the gold standard when it comes to energy-efficiency. Low-E (also known as low emissivity) windows consist of an inner and outer pane of glass. The area between the two panes is filled with an inert (non-active) gas such as argon, which provides the ultimate in insulation without compromising the clarity of the glass. A step down from low-E types are single-glazed and double-glazed windows, which are coated with a transparent metallic oxide finish that prevents some heat loss. These are much less efficient than low-E, which is reflected in their lower R-values. Single glazed windows are glazed on only one side, double glazed are glazed on both the inside and outside. The least desirable windows, in terms of heat loss, are unglazed. An unglazed window is a simple sheet of glass with no coating or insulation. They are more efficient than an open one, but that's about it! Glazing can be combined with low-E for an even more energy-efficient solution.
- Condensation prevention. Condensation happens when there is a great difference in air temperature between the inside of a window and the outside. If the temperature and the humidity inside your home are high, and the temperature outside is low, you will probably see condensation forming. Conversely, the same is true if the temperature outside is quite high and the indoor temperature is cool. Condensation is a problem for windows because when moisture frequently collects around the edges of your windows, over time it will cause damage to the frame and weather seal. It's also a problem because it indicates that your windows are not insulating your home very well. To prevent condensation, look for windows with warm-air technology and high-quality metal spacers along the edges of the panes. The warm air keeps the temperature of the window closer to the air temperature of your home, which won't give condensation a chance to form.
- Solar (UV) penetration. This is an important consideration for anyone living in an especially warm climate. When the sun is constantly shining through your windows, you'll notice that your carpet, furniture and anything else in the sun's path starts to look faded and worn prematurely. To keep this from happening, look for an ultraviolet-blocking coating. This will allow the harmless rays of the sun to shine right through, while blocking the UV rays, which do the most damage.
- Window placement. When you are deciding where to place the windows in your home, consider the fact that south-facing windows let in heat without an undue amount of UV rays. Therefore, they can help warm your home during the colder months. North-facing windows, on the other hand, provide very little warmth and can actually be a hindrance to keeping your home warm. To illustrate this fact, just look at the driveways on your street after a snowstorm. Most likely, the driveways that face south will be melted and clear long before the ones that face north. Therefore, if you are set on floor-to-ceiling windows in your great room, put them on the south side of the house if at all possible.
- Building code requirements. Many states have adopted building code standards which regulate the type of windows which you are allowed to install in a new or remodeled home. Always check your local building code before purchasing or installing new windows. This is especially important if you are buying them from an out-of-state source. Those sold at a local store will most likely meet your state's building codes, but those from an out-of-state source may not.
- Rebates. Some utility companies now offer rebates if you install energy-efficient windows. In some cases, the rebate is significant enough that you will end up paying nearly the same for energy-efficient windows as you would for ordinary ones. Check the website for your local utility company to see if they offer these types of rebates.
There you have it - the world of windows reduced to seven simple steps! Naturally, a well-insulated window is only as good as its installation, so always have them installed by a professional and make sure all of the seams are caulked and sealed well.
