I have an outdoor fireplace that is close to the flue installation phase. The interior dimensions of my fire box is 16.5 inches deep and 24 inches wide. The height to the center of the arch is around 24 inches. The fire brick will extend about 10 inches above the visible box up to the base of the chimney. What would be the correct size flue for this size fireplace. This is an exterior masonry fireplace with no damper. I will be using the square masonry flues.