There is a 6″ flue that will use 6″ stove pipe (stove pipe not included). It is made of 1/4″ heavy duty steel. We roll our firebox (to prevent warping) which means less welds and a longer lasting life. We also use a baffle system so that you don’t lose your heat up the chimney. All of our wood burning units have commercially cast grates and doors, a scoop-type ash pan, and can hold 125 to 150 lbs of rock. In a proper size insulated room it should take 45 minutes to one hour for your sauna to heat to temperature. Will last a lifetime with proper use and care. 1 year warranty.