Hello Xerxes, thank you for your reply. I don't understand why an unused chimney needs to be ventilated.
The fireplace is fitted with a damper, which sounds similar to the hit and miss. It's just not an effective barrier both because it's metal and because its doesn't close with a good...
On this site I found this advice: "If the fireplace is never used, it may be advisable to cover it and seal off completely. It is necessary to fit a 'hit and miss' ventilator to provide ventilation for the flue." Why should the room require ventilation through the flue? No other room has such...