What to Look for in Energy-Efficient Replacement Windows
Understanding Window Performance Ratings:
To buy a good window you do not need to spend more, you need to research better. If you are an engineer then this information will certainly speak to you. If you are not an engineer then let me encourage you to read on. Here you will find a clear explanation of ratings as they relate to performance. Lack of research will almost ensure a bad decision. The proper research will show you the truth.
Energy Efficient Windows:
When evaluating replacement windows we recommend that you look at four ratings in particular. The best products have high energy performance ratings and are very energy efficient. Then we strongly suggest taking a look at who certifies the product and ratings and why the AAMA certification is so important.
Heat Flow (through a window) is what the U-Value represents. The lower this number is then the better it will block heat flow. In Virginia Beach, Va we look for a U Factor of .30 or lower. Air infiltration is a separate issue and is addressed in the Air Infiltration Rating section below. http://smartwebsiteideas.com/
SHGC or Solar Heat Gain Co-efficiency
Solar Heat Gain Co-efficiency measures the transmitting of solar heat. If the SHGC value is higher then more solar heat is being transmitted through the window glass. For colder climates a higher SHGC is desirable and for warmer a lower number is what you want. In the Tidewater area of Virginia we recommend a U Factor between .20 and .30
Design Pressure or DP Rating
The DP Rating of a window can have several variables and so as not to get confusing we will keep it simple here. Basically, the DP test is to measure the strength of the product against hurricane force winds and water penetration on both sides of a window. We prefer a DP rating of 50 or higher, but in some cases a DP-35 will do as long as the window is AAMA Gold Label Certified. In most cases you should not consider the window if it does not have the gold label.
Air loss occurs around our window frames and doors so it makes sense that the more airtight the window is, the better it will insulate. This is a critical rating. Air leakage factors will make or break any window, no matter how well the glass performs or how strong the frame is, so do not overlook this important value. The more air tight the window is, the lower the Air Leakage number will be. A.10 Air rating (or lower) should be what you want for good energy savings windows.
AAMA Gold Label
Window companies that make commercial windows must have their products certified for building code. Many residential windows are not AAMA certified although they should be. When a window is AAMA gold label certified you can be certain that the test results are accurate, that the window will maintain its integrity and that the AAMA will send independent inspectors to each manufacturer, unannounced and twice per year to ensure that the window that was tested is the same as the window that will go into your home. No Matter who you look at Andersen Windows (AKA Anderson Windows), Marvin Windows, custom windows or vinyl replacement windows, do not assume anything without seeing the gold label.
Manufacturers go to great lengths to have their window product tested (by an AAMA approved facility) and Gold Label certified by the AAMA. Always be sure to double check as some manufacturers and sales people will try to mislead you. You will find the AAMA Gold Label in the frame cavity of any AAMA Gold Label certified window.