A Guide to Energy-Efficient Window Performance Ratings
Energy-efficient windows keep your home comfortable year-round with minimal heating and cooling costs. There are several factors involved in the energy flow through a window, which are reflected in a window’s performance ratings. The energy flow through windows can be divided into several categories: solar and non-solar radiation, conduction and convection, and airflow.
Solar Heat
The Solar Heat Gain Coefficient (SHGC) measures the amount of solar radiation that is admitted through a window. The most desirable SHGC depends on your location. In colder areas, a high SHGC rating is good, because it means more heat will be gained during the winter. For hot climates, a lower SHGC means better shading.
Non-Solar Heat Flow
The non-solar heat flow through a window is rated as the U-Factor. This number can be confusing, as it is expressed in units of Btu/hr-ft2-ºF. Most people simply need to know that a lower U-Factor indicates a smaller degree of heat loss and a more energy-efficient window. This is especially important in cold climates, where heat can escape quickly through less efficient windows.
Airflow
When airflow is intentional, it is called ventilation, and when it is unintentional it is called infiltration. Air leakage is expressed in units of cubic feet per minute per square foot of frame area. A low number means low air leakage, which is better for your home environment.
Where to Look
Check windows for an EnergyStar label, or look for a label from the National Fenestration Rating Council, which will display the ratings described above. This label may also provide you with information about condensation resistance and visible transmittance—the amount of light that comes through the window.
Looking to replace your old windows? You can find the energy-efficient windows you need, along with doors, roofing, and your other home needs at Custom Exteriors, Inc. Visit us at our Bay Area location or call us today at (888) 957-7800!
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