Enerzone EUROSTAR Installation And Operation Manual page 62

Instead, if the installation consisted of a horizontal vent coming out at
the back of the stove on a total distance of 4 feet, followed by a tee
and a 6-foot vertical rise, it would be acceptable. The installation end
should be within the allowable configuration zone on the chart since it
would have at least one foot of vertical rise for each foot of horizontal
run. Furthermore, the total vertical rise would be at least 3-foot high.
WARNING: To reduce the risk of smoke spillage there should
always be at least one foot of vertical rise for each foot of
horizontal run. In all cases, at least 3 feet of vertical rise is
needed.
62 Eurostar Installation and Operation Manual