Hi first post -so please be gentle ... We have had our. Chimney capped off onetime ago and vented around the top at same time with6 x3 bricks. We have an electrick fire , when we put this in I blocked the access behind the fire with insulation, on advice I have removed this today as we speak - we were getting sweating marks in the room above on the wall against the chimney. My question is do I need to fit a small air brick inside the base of the chimney behind the fire- or can it be left open , it is an awkward shape really to fit an air brick but if needs then so be it..... Many thanks for assisting ....