bob288, there is very little heat produced by the burner itself, so the warming of the water from heat in the cold smoke adapter in negligible. Removal of moisture from the fish, which is the primary objective won't be hampered by what little moisture may come from a hot biscuit dropping in the bowl of H2O every 20 min. You need proper air flow through the system to remove the moisture from the fish, so keeping an open top vent is a must.