Hi: new to the forum I was shopping for Energy Star windows for an addition and found some Low-E 366 windows I've been surfing the web and haven't found an explanation of the differences and which I should consider "better" without getting too technical any advice on making this choice ? thanks Lew

"Better" for what purpose? There are all sorts of windows because there are all sorts of needs.

There is a windows and doors sub-forum that you might want to look through.

Almost any windows that meet building energy codes will be low infrared emissivity, and therefore, are "LoE." Specifically, LoE-366 windows are low-solar gain windows suitable for use in the southern U.S. where cooling costs are greater than heating costs. These windows may not be the best selection for the northern U.S. where heating costs exceed cooling costs. In those areas, if the house is situated where solar energy is available, then a high solar gain coating like LoE-180 would be preferable.

It is easy to compare the different coatings by looking at tables such as the one at http://www.cardinalcorp.com/technology/reference/loe-performance-stats/. Choose a high heat gain coefficient if you want to have passive solar gain in your house, and a low heat gain coefficient if you want to reject solar gain. The U-values represent the heat transfer coefficient, so the lower the better. There is a correlation between solar heat gain and U-values, with lower solar gain slightly reducing the U-values for everything else being the same. However, high solar gain is more important than U-value if you want to take advantage of passive solar heating.

Lee: thanks for the reply but I am more confused than ever the sites I was checking this morning were stating that Loew-E 366 were good for all 4 climate zones. http://www.cardinalcorp.com/products/coated-glass/loe3-366-glass/ I live in the Buffalo NY area I called Jeld-Wen this morning and the rep said that Low-E 366 were not Energy Star but this afternoon Home Depot and another Jeld-Wen rep said they were going crazy with all this conflicting info :( i'll make Home Depot put it in writing.... Lew

Lew-

Is your house situated such that sun shines through the windows, or is it blocked by forests or other obstructions? If sun shines through the windows, choosing a LoE-180 coating will provide more than twice the solar gain of a LoE-366 coating. In Buffalo, NY you want to take advantage of the solar gain, so choose the LoE-180 coating. If you have good southern exposure, that choice will reduce your energy usage.

On the other hand, if the sun NEVER shines through your windows, there would be a slight advantage of choosing the LoE-366 coating over the LoE-180 coating.

Lee: my house faces South and I get good East and West exposure Hmmm, I think I will avoid the Low_E and just go with EnergyStar for Northern Climate Lew

You might want those Low E windows on the east and particularly the west sides of the house so you don't overheat in the spring, summer and fall. The windows on the south side should have the windows with the most solar gain, since in the summer the sun is high enough overhead as to shade the south side, but provide the sun you need during the fall, winter and spring when the sun is lower in the sky.

-Rosalinda