In short, Low-E means low emissivity, or more precisely, low thermal emissivity.

So yes, Low-E windows are energy efficient because any material that reflects, absorbs, and emits radiant energy is going to save energy.

For example: usually the glass is coated on the inside of the outer pane for double-pane windows.

How do I know if I have low E windows?

How Can Homeowners Tell if Their Windows Have Low-E Glass? The low-e coating is usually placed on one of the inside glass pane surfaces of the insulating unit. Homeowners can test for the low-e coating in a window by doing the following: Hold a lit match or a pen light up in front of the window.

Do Low E windows save energy?

Low-E Windows Benefits and Costs. Windows manufactured with Low-E coatings typically cost about 10 percent to 15 percent more than regular windows, but they reduce energy loss by as much as 30 percent to 50 percent. Efficient windows are defined by the climate of the building in which they will be installed.