When deciding to purchase new windows, there are many factors to reconsider to make the best purchase. Many window sales people will point out the obvious: aesthetics, "cool features" like tilt wash windows, and warranty. As consumers get more energy conscious, an additional one factor comes to the forefront when selecting to replace windows: window ratings. While many window salespeople will focus on the big two: U values and Solar Heat Gain Coefficient, there is an additional one important factor to reconsider when selecting windows: air infiltration.
Air infiltration does not get its due when inspecting replacing your windows, but it is a major culprit for heat gain and loss in a home. An older window does not seal as tightly and creates the opening for air to enter into the house. people refer to this as a "drafty" window in the winter because the cold air is literally entering the room. Heat also enters the house in the summer straight through cracks, however, many people mistake this for the heat arrival in straight through the inefficient glass.
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There is a scientific way to rule air infiltration beyond just standing next to a window and calling it drafty. Air leakage is measured by the testing of a thorough sized window. The window is installed in a testing wall. A vacuum is of 75 pascals (1.57 psf) is applied on one side of the test window. This corresponds to almost a 25 mph wind blowing perpendicularly to the window. Flow meters are positioned to portion the rate of air leakage. This is divided by the total window area to get a reading (in the U.S) in cfm/ft2 (cubic feet per minuscule per foot squared) to the nearest tenth (i.e., a test value of 0.17 would be given a rating of 0.2). The best inherent rating by the Nfrc is 0.1, as they will not round to 0.
So why are more salespeople not discussing air infiltration when touting the performance of a window? Currently windows are not required to be tested for air infiltration performance. If a business chooses to have its stock tested, it cannot have more than 0.3 cfm/ft2 of air leakage. If this maximum value is not met, the energy loss straight through air leakage is likely considerably less than that straight through heat loss across the glass or frame. Regardless, air infiltration has a major consequent on perceived performance of the window. The reality is that even at the passing value of 0.3, a window will still exhibit noticeable drafts colse to the elements of the windows.
Certain window types are designed to seal tighter than others and thus supply lower air infiltration numbers. Casement and awning windows (think crank deal with to open and close) offer the best performance because as the window is closed, the locks pull the sash tight against the frame. In addition, as the wind blows against the window, it pushes the sash tighter against the frame.
Double hung and singular hung windows are not as air tight because they rely on gaskets and weatherstrip to forestall air infiltration colse to the sashes. Hung windows do not have any overlap or compression fit in the middle of the sashes so as the wind blows against the window, the air can get in the middle of the sashes and create a draft.
Horizontal sliding windows are the biggest air infiltration culprit because the operable sash is simply sitting in the frame. While many modern sliders have weather strip and gaskets to try and sell out air infiltration, the windows are still more prone to movement in the wind.
While it is not a required portion for window performance, air infiltration can not be ignored when selecting windows for your home. It does not matter how great the low e is, or how insulated the window frame is if the window leaks like a sieve, the energy efficiency problem has not literally been solved. Pay concentration to the air infiltration, see how well the stock is sealed at the joints, know which types are best for your climate, and you will make the best purchase for your exchange project.
Air Infiltration in replacement Windows - The Forgotten Window Rating SLIDER CASEMENT WINDOW AIR CONDITIONER
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