Size of Vent Duct for two kilns

We just installed a new L&L kiln (Model e23T-208, Serial # 050916-B-CWK) and L&L Vent-Sure Downdraft Kiln Vent System with the Vent Doubler System so we could also vent our existing Skutt KM1023. My question involves the size of the central duct (which I understand to be the flue that exits the room). If I understand correctly, on page 6, the kiln vent manual states that for 2 kilns the central duct should be 6”. PLEASE KEEP READING! Our central duct is 4”, BUT we will ONLY BE CAPABLE OF FIRING ONE KILN AT A TIME. With the idle kiln dampered off, will the 4” central duct be adequate/acceptable for this situation?



The volume of air to be moved is actually for one kiln at a time only in this scenario so a 4" duct is perfectly acceptable. Some general thoughts: The table on page six of our instructions is meant as a general guideline in any case. The larger size of the duct reduces the static pressure which allows a higher volume of air to flow assuming the same input (our fan in this case).