In order to choose the best replacement home windows, understanding the way a window works is important. There are four main factors that windows are designed to either increase or reduce.
The first of these factors is radiation. Radiation is the movement of infrared heat energy through the glass. Low-e coating helps bounce radiation waves back inside the home, reducing winter heat loss. Specialized glazes reduce the amount of summer heat gain let into your home. This in turn helps reduce the amount of air conditioning used during warmer months.
The second factor is conduction. Conduction is the direct transfer of heat through the window from the inside to the outside of your home. Conduction and radiation allow heat to escape and cause greater use of your heating or air conditioning.
When warm air circulates and hits the window, the window absorbs the heat and releases cold air that sinks towards the floor. This process is called convection. To reduce the effects of conduction and convection, insulators are used in windows. This prevents heat transfer and keeps the window from absorbing the heat and releasing cold air in its place.
Air leakage is the amount of indoor air that escapes through gaps in the window frame or weather-stripping. Ideally, high quality windows will prevent air from escaping through gaps between the window and the frame.
To address each of these actions, coatings, glazes, and insulation is made for windows to combat opposing temperatures. These enhancements keep warm air in and cold air out during the colder months. Likewise, during the warmer months, the warm air is kept outside your home while maintaining a cooler temperature inside.