How to cover this wall ventilation?

Question

I recently moved into a house where each of the three bedrooms contained one of these:

I'm guessing it's used for ventilation. Problem is, winter is coming and I don't particularly enjoy having a cold breeze during this time of year (also, the sound from outside can be quite clear and annoying).
What's the best way to cover this up either temporarily or permanently?
Some details of my house:

Built around 1953
Outside is brick covered with rendering
Living in the UK

Mazura · Accepted Answer

Are you sure these aren't part of your HVAC? If I had to guess, these are natural draft returns to the boiler room. If your heat comes through a grate in the floor, you need these.

Ok, you have radiators, so these probably are just fresh air intakes. Covering them or not is your prerogative.

Temporary solution: tape some card stock over the opening.

Semi-permanently: use a can of spray foam to totally fill the duct. You may need to get the grate open to stuff something in there, so the foam doesn't just drop down into the duct.

Permanently: remove the grates, and if necessary, remove or bash the remaining duct work into the wall with a hammer so that you can plaster over it, after having stuffed a piece of batt insulation into the duct.

Magnetic duct covers are another option.

Alastair McCormack · Answer

They were very popular in 1930s houses. Smaller semis would have them in the box room at the front and bathroom at the back.

You can safely fill them in as long as you don't have a gas appliance (which you don't) or fire in the room.

Often these vents are vented into the wall cavity, which should make it easier to fill in with expanding foam.

Be warned that you may find that these vents were providing useful ventilation that you will lose on blocking up. It's not often a problem of its period as it'll be quite leaky. If you don't have window ventilation / weep holes, you may find moisture on your windows once the holes are blocked. If you do, consider fitting weep holes or a whole house ventilation system.

HABO · Answer

You could cover them with panels secured with toggle bolts. If you decide to uncover them in the future you'll lose the toggles in the wall, but that shouldn't be a problem.
The panels can be as simple or complex as you care for. Thin plywood would suffice to block most airflow. Opaque Perspex with an EPDM gasket around the edge would be moisture resistant and provide a decent seal. A layer of open-cell foam (on the grill side) would help attenuate noise.

How to cover this wall ventilation?

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