Can I block up the vents in my old double brick house? I am not sure why they are there, but I imagine they are not good for losing heat and probably lead to dust.
There is, but we don't use it. So you think the vents are only necessary for ventilation for when you have a fire?
I would recommend against blocking up those vents as it will lead to a build-up of moisture which then leads to mould. The property my friend rents has those types of vents painted over and sealed and she is constantly dealing with moisture and mould, it’s not pretty. An alternative solution is to maybe get something that can go over those vents that can still allow for ventilation but keep out dust and other particles.
Fire or unflued gas or electric space heating that will deplete the oxygen in the air and send you permanently to sleep overnight. They were replaced in modern house by slits in their aluminium window frames.