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

enter image description here

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
  • You forgot to ask if you should ;) What type of heating system do you have?
    – Mazura
    Oct 14, 2016 at 22:34
  • @Mazura, should I? :). It is central gas heating so we have radiators in each of the bedrooms.
    – user35594
    Oct 14, 2016 at 22:41

3 Answers 3


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.

  • There is no boiler room that I am aware of and no grates on the floors (it's all carpet).
    – user35594
    Oct 14, 2016 at 22:45
  • Thanks for your advice, I will look into the different solutions!
    – user35594
    Oct 15, 2016 at 9:53
  • 1
    HVAC and boiler room in a UK house!? We wish! Nov 13, 2016 at 21:00

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.


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.

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