SHGC has to be .30 or less to qualify for the Energy Tax Credits, so you have gone as high as you can....and still qualify.

I would ask, why don't consumers educate themselves better before making a large purchase so they are aware of all the options?

To answer your question, yes you are going to notice a difference. Had you done some research you would have found that adding LoE glass to any window or door reduces the solar gain but it also reduces the heat loss. So it's a trade off to a certain degree. Most manufacturers offer higher solar gain glass than what qualifies for the tax credit. You could have gotten a single coated LoE glass for those windows and still maxed out on the tax credits on the other ones.

At this point, I would ask what the upcharge would be to replace the glass in the south facing windows. Be prepared to pay extra. Next time, come on this board before you make a purchase like this.

research is what most people fail to do, or from the correct source. Energy Star and sellers of 'big brands' push low U down your throat so its understandable to focus on that to hit energy credits. However with Marvins, you hit that credit pretty fast. Truth of it is, depending on how your house is designed solar wise, picking the correct windows that do not hit the tax credit might end up saving you more in the long run anyway. Most high SHGC windows (.5+) have Us higher then .3. But your gains will be more worth it.
Bottom line you will notice a difference, however I would not say its worht any additional cost or upcharge IMO. If you were designing a direct gain solar house in a cold climate as I am, then yes, it would make a big difference.

FWIW, Cardinal produces a 179 glass the has a pretty good U value, and a fairly high SHGC. Might check it out.

Thanks. I should have known better - I use this site all the time. Most of windows are blocked by a neighbor's house and a tree, so I am making myself feel better by remembering that the direct sun only comes through for a couple of hours in the middle of the day. Only the sliding door has unobstructed southern exposure - I can always open it to get the full sun. On the positive side, I will look forward to having a couple of drafty areas become more comfortable for the majority of the day. And the glare will be cut down. I can always add skylights later.

Just a quick update... The windows are installed and they aren't as bad as I had feared. I can still feel the warm sunlight come through the window and the blinding glare has been reduced. They are working well so far with the winter sun.

This is a big reason I passed on the tax credits. A bad tradeoff for low-light February in Alaska.

The tax credit requirement for SGHC ran directly counter to the recommendations of the Alaska Buildling Science Network factsheets on windows.

Well this, and the incredibly high replacement costs for the windows I was quoted helped me decide too.