Energy Efficient Windows Block Out Drafts
Did you know that the U.S. Department of Energy states that 10-25% of the energy that you use to heat and cool your homes is lost through inefficient windows? When it comes to new window installation, air infiltration is a major factor for cold climates.
What is Air Infiltration?
Air infiltration is the process of unwanted air from the outside making its way into the interior of the home. It’s the cold draft that you feel while you’re sitting by a window in the middle of winter. You can test if your windows are drafty by lighting an incense stick and holding it close to the window. If the smoke moves horizontally, it’s likely that you’re experiencing drafts.
Drafts enter through various points of the window, including:
- The sash
- The sill
- Where the sash meets the sill
- The perimeter
- Where the sash meets the rail
The most energy efficient windows in MA are measured in cubic feet per minute (CFM) with the average industry rating between .12 and .3 CFM. Windows that contain the lower rating are losing roughly 24 cans of air per minute. The best windows lose only 0.8 cans of soda per minute.
Keep in mind that there is no such thing as a window that is 100% airtight. Air can even move through the cavities of an insulated wall! However, for the window to be energy efficient, it must have as little air infiltration as possible.
Air infiltration is undoubtedly important, but there is another major component to consider with energy efficient windows: the glass package.
Cold Weather Components of a Glass Package
Just like air infiltration performance, not all glass packages are created equal with replacement windows in MA. You’ll find that some windows don’t come with any of the important technologies at all, resulting in your home that always feels cold during the winter.
What are the most important window technologies for cold weather climates?
- U-Factor: A window’s U-Factor determines how good energy efficient windows are at preventing heat loss during the winter. The ratings range from 0.14 to 1.20. Replacement windows with a low U-Factor provide the best insulating value and higher resistance to heat flow. When your U-Factor is on the higher end, heat is easily lost through your windows in the wintertime.
- Solar Heat Gain Coefficient: This metric ranges from 0-1. It measures how well your windows block heat that’s created by sunlight. Whether it’s summer or winter, the sun can warm your home through the windows and in some cases cause overheating in hot weather. However, the right rating (and comfort level) depends on the climate. For us homeowners here in MA and other areas of New England, we want a higher SHGC rating. This allows the sun to help naturally heat the home in the winter. Without the proper SHGC rating, your home will feel cold throughout the entire season.
- Low-e: Low emissivity glass contains an invisible layer that’s thinner than a human hair. In cold climates, low-e coatings applied to the interior glass of the windows prevent heat loss. In fact, they can help reduce heat loss by as much as 30 to 50%!
- Argon and Krypton: Argon and krypton are natural gases that are also invisible. These gases are denser than air and belong to a special group of gases known as inert or noble gases. Their purpose is to provide thermal efficiency to the window, and the heaviness of the two gases increases insulation and further prevents heat from escaping.