Judd is a window and door specialist working at Preston Feather Building Centers’ Harbor Springs, Michigan location.
~ Judd Petro, Window & Door Specialist, Harbor Springs Michigan
There are several key terms to become familiar with when shopping for new windows. The terms we have listed here refer to the characteristics of windows and their insulating qualities. Familiarity with them will help you become more knowledgeable of potential energy savings and the insulation value of windows, and will help you determine the best combination of value and expense for your budget.
From Andersen Windows and Doors, here are a few important glossary terms:
Air infiltration: Industry test that measures the amount of air leakage through a window or door (the lower the number the better).
Argon gas: Colorless, odorless gas used in the air space of double pane Low-E glass to increase the insulating performance.
Bay window photo courtesy Andersen Windows & Doors
Condensation: Water that collects as droplets on the glass/sash/panel interior or exterior under certain conditions (typically cold surfaces when exposed to humidity).
Dual pane/Double pane glass: Two panes of uncoated (non-Low-E) glass with an air-filled cavity (not argon-blend gas-filled)
ENERGY STAR®: A government-backed program to help consumers identify energy efficient products.
Insulating glass unit: Two or more glass panes that are sealed together to increase energy efficiency
Laminated glass: Layered glass that resists breakage and holds together when broken
Low-E glass: Glass with a low-emissivity coating that restricts heat loss
NFRC: National Fenestration Rating Council is an non-profit organization that provides for fair, accurate and credible energy performance ratings for windows, doors & skylights.
Outdoor/Indoor Transmission Class (OITC): Measurement standard used to indicate the rate of sound transmission between indoors and outdoors (see also STC)
PassiveSun™ glass: Andersen brand name for a glass type ideal for situations where solar heat gain is desired, typically in passive solar building designs.
SmartSun™ glass: Andersen brand of a glass option that reduces solar heating but allows high visible light transmission
Solar Heat Gain Coefficient (SHGC): A measurement of the sun’s heat energy that passes through the window/door. The lower the value the less heat gain thru the product.
Sound Transmission Class (STC): Rating system used to measure how much sound is transferred through windows/doors (see also OITC)
Sun glass: Tinted glass that reduces heat gain
Triple pane: Glass construction consisting of three distinct layers of glass and two air-spaces
UV protection: Percentage of Ultra-Violet (UV) transmission from the sun’s energy; the lower the number, the potential for reduced fabric fading.
This illustration from Fine Homebuilding demonstrates how air flows through windows.
In addition, it is important to understand how heat loss occurs through windows by radiation, convection, and conduction. As defined by Cornell University:
Radiation is heat passed from a warm object to a cooler object. Heat always moves from warm to cool. If you are near a cold window, your body heat will radiate to the cooler window, making you feel cold.
Convection is heat transfer through a fluid such as air or water. Air infiltration through cracks around the window increases convective air movement and heat loss. This explains why caulking and weather-stripping to reduce air movement also reduce heat loss.
Conduction is heat transfer through solids. Glass is a good conductor of heat and therefore a poor insulator. Heat readily passes through glass.
(Written by Gwen Cukierski and Regina Rector; Reviewed and revised by Mark Pierce, Extension Associate, February 2006; Department Design and Environmental Analysis, Cornell University)