[Zeke]

I've been installing windows and doors with LowE for 20 years. It works. You can have it in the window so the heat stays inside or the heat stays outside or both. Actually, it works on infrared rays going in each direction, but the effect can be maximised by which internal glass surface the coating is placed.

Then, you can upgrade to LowE on both internal surfaces. Some companies call that LowE "squared," or LowE 2. LowE also reflects UV rays pretty well, but there's no heat gain or loss with UV.

Here's what the sales people don't tell you: and window is only a small part of the total energy envelope. Most houses have around 10% of the floor area for window area allocation. If you add in outside facing walls and ceilings to attics, your total fenestration could be as little as 5% or even less.

You can't ask something that is 5% of the envelope to produce dramatic energy savings. It will help, of course, because you will be reducing convection through the windows to almost zero. But heat gain on a 2 x 4 studded wall with little or no insulation facing the sun will heat up a room faster than Sarah Palin walking into a democratic caucus.

And know this fact: the best window you can buy is about an R5 with most being around an R3. That's why they don't rate window performance on the R scale. They have there own "emittancy" scale. Go for a product that is close to 40 on that scale.

And do the rest of the stuff on the energy savings list like fully weatherstripping all entry doors and back-damping any vents to the outside. Fully insulated attics have been shown to be the best investment. You should have about an R40 up there.