WindGate Energy Efficiency


Insulating glass package combines low emissivity (Low-E) glass with a warm edge spacer to optimize the balance between radiant heat loss, passive solar heat gain and visible light transmittance.

Your Invisible Barrier

When you consider energy efficiency, perhaps the most critical part of any window is the insulating glass system. It only makes sense: the glass has the largest surface area.

Windows Can Help

To understand how windows can help, you must first understand that energy is lost through windows in three major ways: conduction, convection and radiation.


The framing of all Alliance windows is made from vinyl, a natural insulator. To prevent energy loss through conduction, all insulated glass units utilize Duralite® warm edge technology. Using a low-conductance spacer, this method assures maximum resistance to energy flow.


Energy can also be lost through natural convection currents that can form within the insulating glass. That’s why Alliance InnovativE® glass is 3/4″ thick, shown by government testing to be the optimum dimension to prevent these convection currents.


Radiation occurs when long wave heat energy moves toward cold areas.

The most effective barrier to radiation is an optimal special Low-E coating, a standard part of our InnovativE® glass package.

This special coating actually reflects the long wave radiation back to its source.

This is important to understand, as radiation affects energy consumption, no matter what part of the country you call home.

Solar Gain vs. Heat Loss

The concerns of homeowners in the North are quite different than those in the South.

In the North, where heating is a concern, glass must allow maximum solar gain, while preventing heat loss.

NFRC Ratings with Low-E and Argon Gas Fill

Product Series Operating Style U-factor w/ Low-E & Argon Gas Solar Heat Gain Coefficient Visible* Light Transmission
Windgate Double Hung 0.29 0.28 0.53
Windgate Single Hung 0.29 0.29 0.56
Windgate Double Horizontal Slider 0.29 0.29 0.54
Windgate Single Slider 0.29 0.28 0.54
Windgate Picture Window 0.28 0.30 0.57
Windgate Casement/Awning 0.27 0.27 0.51
Windgate Patio Doors 0.29 0.30 0.57

*Architectural drawings and structural tests/ratings available upon request