Any window is energy efficient compared to no window, Star is an EPA certification level. IIRC Anderson does have a line of Star certified.

Compare the thermal characteristics of your windows to a Star certified window, then come to your conclusion

My climate zone is Northern (in Massachusetts near the Atlantic shore). Andersen sells an "eco-line" that is star certified but it's MEGA expensive. My most expensive window is a casement in the 400 Series (a good level series) & it isn't energy star certified. i guess i'm surprised that in order to get an energy certified window from such a reputable company would require a bank robbery ;) I thought it would be more of a standard feature. so that's what made me ask if it has to be certified to be energy-efficient.

I appreciate any further feedback!

Jim-

How far off is acceptable. in some cases my window choices were 0.02 or 0.03 off on the SHGC (for the given U-factor). But my most expensive window is off by like 1.06! But I'm not sure what's an acceptable devotion & what's not in order to ensure energy efficiency.

Passive Low-E 4 should get get you energy star. Should be about .29 U and .52 solar. It is not in there system at some Home Depot’s , so the may have to call Andersen.

Carol -

Energy star makes some generalizations and some mistakes. Particularly when it comes to passive solar and window orientation. Don't feel you have to be ES certified unless you need to be for a rebate or house certification.

There are 2 numbers to care about

SHGC - which is the amount of heat gained through the window. A low number means good for reducing a/c. Means very little on a North facing window or appropriately shaded South window.

U. factor. This is probably what you care about in Mass. This is the resistance to ambient heat flow. It is how cold the window would feel in the winter. It is minor in the summer. Yes Anderson charges a lot for their low u window. Do you have an energy rater to decide if it makes financial sense?

$5000 extra on windows that should last 30+ years isn't a huge deal. Note that low u windows will make the temps in your house more stable in the winter since windows won't be robbing the heat. So it isn't just energy savings but comfort also.

What I know about Mass. is energy costs are high and it gets cold. I hear shocking numbers on what people pay for heat. Down here in NC, different story and I couldn't come close to justifying low u windows. Not with heat pumps using $.10c a kwh electricity. Solar panels pay off decades faster.