I was playing with the hvaccalc options for windows and it seems the single best option for saving on cooling for sun facing windows is reflective coating. It cut the heat gain down to a third. In comparison triple pane did not seem to help at all. Does this seem corect to ya'll? I am not sure what this reflective coating is so I sent the creator an email. Thanks

Yes- any low-E coating , particularly on the exterior glass of a double-pane window trumps triple panes by a wide margin for killing off solar gains.

Indium tin oxide is the most commonly used hard-coat low-E coating. It's usually placed on the sealed side of the exterior glass on heat-rejection double panes used in cooling dominated climates, but on the sealed side of the interior glass on double panes suitable for heating dominated climates. The difference in solar gain changes only slightly by whether it's on the interior vs. exterior pane compared to coated vs. non-coated. In US climate zones 1-2 it's generally better to put it on the exterior (particularly on the west facing windows) but in 4-7 it's generally best placed on the interior. For zone 3 putting it on interior pane for the south facing glass and the north facing glass and on the exterior for east and west facing glass is likely the best compromise- it rejects the low-angle sun in summer, yet allows more wintertime gain. In summer overhangs and the high sun angle limit gains from south facing glass, but not from east or west facing glass.

The SHGC rating of the window is key to cooling season performance, more so than U-factor, and a window with the same factor will have a lower SHGC when the coating is on the exterior glass, even with the same visible light transmittance.

There are even more reflective sputtered silver or gold soft coats, most-often used for very-reflective windows designed to take the gain out of commercial buildings with mostly-glass exteriors, but they're used in residential apps as well where cooling load performance is critical. And there are other soft low-E coatings of different selectivity used in very high performance windows.

The program actually had a seperate option for low E glass which I selected. That's why i was a little confused about the reflective coating being a different option that could be used in combination. Are most companies glass coating the same? Or are some far and away better than others. Also should I be worried about reflecting heat away from my south windows if I can get good 2 feet overhangs on them. Thanks

Most manufacture use similar coating materials, but the materials differ depending on the performance goals (lower solar gain vs. lower U-value.)

2' overhangs are pretty good for summer shading south facing windows @35 degrees north latitude. There are overhang design tools out there for dialing it in, if you care to get into it, but it's pretty simple solar geometry.

Rejecting the heat on the west facing windows has the biggest effect on the peak cooling, since overhangs, since the house is already cooking in the PM when the sun drops below the 2' overhang, and it takes a HUGE overhang to reduce even the 4PM west side gains. On the east side it's the same gain factors and the same number of BTUs, but it has a negligible effect on the system sizing since those gains occur well before the siding and roof have come up to temp. East facing window gains increase the average load far more than it affects the peak.
s

Agree - avoiding / managing / filming / shading west glass is our greatest challenge in the sunny south.