Thermal Windows | Thermal Replacement Windows

Thermal Windows | Thermal Replacement Windows

Most thermal replacement windows have either double or triple panes of glass. The multiple panes of glass are what make them so efficient, and depending on the materials used and some of the ratings of those materials, the windows can allow less air and heat transfer between the interior of your home and the exterior. By doing this, thermal replacement windows can lower your heating bills in the winter and your cooling bills in the summer, and in many cases this savings is quite a lot. In fact, the higher your utility bills were and the older and draftier your windows were, the more savings you can usually expect to see on your fuel bills. On average, most homeowners save about 20 to 30 percent off of what they were previously paying before their new windows were installed.

There are a few choices you have to make when choosing thermal replacement windows and some of them may be a little confusing without some knowledge of what they mean. Options such as U factor, solar heat gain coefficient, condensation resistance, air leakage and visible transmittance may sound a bit foreign to you but they all relate to the efficiency level of thermal windows and by understanding what some of these terms mean, you will have an easier time choosing the thermal windows that are just right for you. Below is a description of these terms.

U Factor – The U factor is the single most important rating for homeowners to consider when purchasing thermal replacement windows, especially for those living in colder climates. U factor ratings measure the amount of heat loss that occurs through the window. This is such an important rating factor because heat loss is the main reason people seek to replace their old drafty windows in the first place. The U factor rating system was developed by the NFRC (National Fenestration Ratings Council) and most windows have U factor ratings between 0.2 and 1.3, with the numbers on the lower end of the scale being the best. For example, windows that have a U factor of 1.3 are usually old metal casement windows, while some of the most efficient thermal windows that have triple panes of low-e glass have U factors of 0.25. Most decent single pane windows have U factors in the 1.0 range, and if you add a storm window that rating falls to around 0.6. Double pane windows with low-e glass are even better than that, falling in the 0.4 range, but cannot compete with the extremely efficient triple pane windows.

Solar Heat Gain Coefficient – This is pretty much the opposite of the U factor. While the U factor measures how much heat loss occurs through the window, the solar heat gain coefficient measures the amount of heat gain that occurs throughout the warmer months. For those homeowners that live in warmer climates, this number is equally as important (or more) to the efficiency of their windows as the U factor. Ratings of solar heat gain coefficient range from between 0 and 1 with lower numbers being more efficient.

Condensation Resistance – This rating measures how well a window can resist the formation of condensation. For those homeowners that live in very humid climates, this is an important rating to consider, although condensation issues are becoming a bigger issue for many homeowners that have well insulated or poorly ventilated homes in an effort to be more energy efficient. These rating numbers are better, the higher they are.

Air Leakage – This is another important rating that determines how energy efficient your new windows will be because it measures how much outside air will be able to flow into your home through the windows. Ratings are usually between 0.1 and 0.3 and fixed and awning style windows usually top the list of the window styles with the least air leakage.

Visible Transmittance – This rating has less to do with efficiency than the previous ratings and more to do with personal preference. Visible transmittance (or VT) measures how much light can pass through the window. The higher the rating, the more light that will pass through the window and brighten up your home.

In addition to these ratings, there are a few other choices to consider when purchasing thermal replacement windows. There are a wide variety of new technologies that are on the market and allow for the production of many different types of windows with different features. Some windows have low-e glass that adds to the efficiency. Others have argon gas between the panes. Some windows require virtually no upkeep because of the materials used to construct the frames (such as vinyl). All of these window choices, in addition to the efficiency ratings described above, should be considered before deciding which type of thermal replacement window is right for your home.