There is/was a massive hole in the wall of the house we have just bought and it just had a plastic vent cover over it on the inside and needless to say it felt like an air conditioning duct as its 4″ wide at least.

The house has or did have enough draughts, not to mention an open flue gas fire in the opposite room with just one door behind so using the fire was a thankless option as it acted to cool the house being as it was like a colander.

The question is, am i likely to die from carbon monoxide poisoning without said vent (which is now full of expanded foam), and if i do need a vent can i get away with putting a pipe through the wall next to the fireplace which vents the fire under the grate or does that not solve the problem?

Its great having an open fire but by christ they are damn inefficient things

Get a Gas engineer etc on to give you a proper opinion based on being there- looking around. Most likely he’ll say ‘look, see that over there etc’. DONT just block it up.

If there isnt a gas appliance in the room it wouldnt bother me blocking it

Just done the same in my spare room as it had a similar vent in place….

The boiler used to live in there hence the vent.

Its possible you had a gas fire in your fireplace at so,e point which needs venting

None of the houses ive lived in growing up ever had vents in for open fires nor even the wood burners.

When I had cavity wall insulation installed they said they have to put a vent in to my sitting room as have an open fireplace there. I made a fuss but got nowhere. So I let them put it in then blocked it.