What is an air infiltration rate, and why is it important?
Properly made and insulated windows are a must, because if air from the outside can enter your home through cracks in the window, then energy efficiency and comfort are compromised. To combat this, the industry adopted a measurement system from the American Society for Testing and Materials (ASTM) called the Air Infiltration Rate.
The air infiltration rate is a measurement of the amount of air that can pass through a window. It is expressed in terms of a number assigned by an independent laboratory after significant testing.
The lower the air infiltration numbers, the lower the amount of air passing through the window, thus less heat loss. Windows that are able to stop drafts will use superior weather stripping and incorporate fusion welded corners that eliminate seams and potential leaks. Cold spots, or that drafty feeling, are eliminated, thereby reducing your energy costs. So look for low numbers on air infiltration test results. Don’t accept any window that has an air infiltration rate of more than 0.07 on double hung or sliding windows, and expect even lower rates on casement windows.
What is an R-Value and how important is it?
“R” stands for resistance. The higher the “R” factors, the better the insulation characteristics. The “R” value of a windows frame and glass is very important since it directly relates to how well the window will reduce energy consumption. A higher R-Value will perform better in reducing energy costs than a lower R-Value.
In fact, you do more to reduce heat loss by switching from an R-2 glass (like in a double pane window) to R-4 glass, than by raising the insulation value of an equal area of R-11 wall all the way up to an R-100!
Building components with low R-Values allow large amounts of heat loss (and gain) to occur. It has been estimated that 25%, or more of a home’s heating and cooling energy is lost through windows. So even a minor improvement in the insulation value of a single component, such as the glass or the frame, can dramatically reduce winter heat loss and summer heat gain.
What is warm edge technology?
“Warm edge technology” is the ability of an insulated glass unit to create a highly effective thermal barrier against the transfer of heat or cold, keeping the edge of the glass “warm”. In an insulated glass unit, the spacer is a primary point of transfer for heat or cold through the window.
To combat this transfer, a barrier is established by isolating the spacer material from the glass. This is accomplished by using a non thermally conductive material, such as a high performance polymer or polyisobutylene, to keep the glass away from the spacer.
The most advanced systems use two separate spacers to create a complete thermal break. If a window manufacturer does not use some type of warm edge technology in the manufacturing of their glass units, you will notice more condensation on the interior pane of glass, and in the winter, the interior pane of glass will be cold to the touch.
Is all window glass the same?
No, not all window glass is the same. There are several different colors of glass available, from gray or bronze to green or blue. Also, window glass comes in a variety of thicknesses, from single strength (3/32″ thick) all the way up to 1/4″ or thicker.
The one thing common about all these glass types is the rating system. Like a window frame, glass is rated by R-Values, the higher the R-Value the better the glass performs. The type of glass, its thickness, the number of panes, the distance between the panes, even the manner in which the glass panes are connected all have a bearing on how well the glass performs.