The purpose of a flue, of course, is to provide ventilation. Exhausts travel out the flue and act as an exhaust pipe. Outdoor fireplaces don’t always need flues, but I’d highly recommend one. I especially recommend flue for enclosed porches. A flue liner is excellent for those windy days. That’s because it will provide direction and stability. Without a flue, it’ll be challenging to control the direction of flames and exhaust. You can also opt for a smoke shelf, which prevents rain and other elements from getting into your fireplace. If you decide against a flue liner, make sure it complies with outdoor fireplace regulations.