I just make the desired quantity of hot tea, and add ice.
My MIL made southern iced tea. She boiled 2 quarts of water for 10 minutes with 5 tea bags. Yes, boiled with the tea bags in the pan. After cooling on the stove, she then filled a 2 quart pitcher 1/3 of the way with sugar, added the cooled tea and diluted ( if needed) to 2 quarts.