I am trying to install a Jotul F3 into an existing Heatform metal firebox. Stove will set on hearth and I already have a plate to cover the firebox opening. (1) Do I simply cut out one of the air flow pipes blocking me from getting my stove pipe up through damper? (2) Do I need to seal up around the new stove pipe or leave it open. The place that I moved the stove from simply had a stainless pipe up through the damper.