1930s house. Back bedroom has a large old air brick vent near the ceiling, covered by a plastic grate which can be slide closed.

Can hear the road noise through it badly and worse I think next door smokes by their backdoor which is right below the vent.

So what is best to block it up with? Will only have access from inside it is recessed by about 2cm so tempted to cut a bit of mdf to size, screw in and skim over.

Or would I be best off trying to chisel the whole thing out and brick up? Bear in mind I have no access to the other side and it’s within a meter of next doors back door

It’s there for a reason so be careful just blocking it up. Houses need to breathe.

^ chances are it was there in conjunction with a fireplace in the room.

Open fire place long gone. And now has double glazing. Plenty of drafts in the old place. Air bricks beneath floor level all round (and when I had the carpet up fitting cabling a gale was blowing under there)

No other evidence of bedroom vents in any other room so they have been long removed. Even if causes an issue it isn’t that difficult to reinstate if I screw a bit of mdf over it.

Blocked ours up years ago. Similar 30s house. No ill effects.

In your case I’d maybe stick some plasterboard in with some blobs of easifil then smooth some more easifil over the top.

Conversely the previous owner of my place blocked them up and we had horrendous condensation problems in the bedroom. Our fireplaces are also removed.

Once we opened the vents up again, problem gone.

I’d leave it, but maybe fit some sort of directional cover outside to permit air in but restrict the noise a bit?

My experience was the same as that of bensales

Mines was there for a long defunct boiler in the back bedroom so I felt it wasn’t needed.

Got condensation and damp in that corner so opened vent again and no issues.

What I did in end was fill the cavity between vent plates with borken up insulation with big gaps to defuse air from gusting straight in but still let it breathe

Best of both worlds

You can buy acoustic vents which may help.
Google ‘rytons’.

Maybe some kind of porous sponge or foam, so it can still breathe but should help baffle noise and smell?

Block it up then open all your windows wide for ten minutes everyday.

Then shut them and let the fabric of the building heat up the new air.

My experience is that blocking up all sorts of holes in a draughty house has warmed it up considerably without causing any damp problems. Probably depends on how many remaining holes there are – in our case, plenty still!

I would start by blocking it in a temporary and reversible manner (eg just put something over it) and see what happens.

What about polystyrene? Any good sound/smell insulation? I have a garage full of the stuff at the moment from new appliances. Could use bathroom sealant to hold it in place. Would take about 15mins to cut to size and fit, even less to remove.

^ chances are it was there in conjunction with a fireplace in the room.

I’d have thought a fire vent would be at the bottom of the wall? There’s little point in siphoning away carbon monoxide when it reaches a height of eight feet.

As others have said, old houses need to breathe. Modern double glazing, replastering, paint, and no vent bricks will spell death for it.

I’d have thought a fire vent would be at the bottom of the wall? There’s little point in siphoning away carbon monoxide when it reaches a height of eight feet.

Surely the purpose of the vent is to ensure there is enough fresh air in the room to allow complete combustion and prevent carbon monoxide in the first place? Not to let the carbon monoxide out once it has formed.

All ours are about a foot below ceiling level.