We like to say our windows are; "Made in the South...For the South"! The climate in the south is far different then the climate in upper northern states. Through out the year it's much hotter in the South for much longer. So windows should be designed with this in mind. In the north they want the sun's heat to pass through the glass (High SHGC). It helps heat up the house during their long cold seasons. Many windows are tailored to deal with the northern climate. Ours are different.