Is it at all sensible to fill in this vent? Maybe with expanding foam or similar?

This is a 23cm by 23 cm vent in the cupboard in the corner of my kitchen, it goes through the entire wall, and it is covered by a thin plastic vent on the outer wall, it makes the whole room freezing. I live in a 1960s build 3rd-floor apartment with central heating, what is the need for such a gaping hole in the wall? I only just discovered it, it was completely taped up and had been for at least 6 years.

  • 1
    Do not like to suggest to seal an unknown vent, abandon one yes. Ask the landlord what it is for, then you can seal it up if it is not used anymore for something. That size probably want insulation in it instead of expanding foam(usually for small stuff).
    – crip659
    Dec 2, 2021 at 11:50
  • Wow... took a minute to find that in the picture. Does it open directly outside? Do you see daylight when you turn off the lights? I'd second the suggestion to check with the landlord or other tenants to see if they have them, too. Since you're storing paint right there, the vent will help should there be any spills. What else is in that closet?
    – FreeMan
    Dec 2, 2021 at 13:38
  • Is your cooktop/stove/oven/range/hob/(any other terms for the main cooking appliances, or combined pair, in a kitchen I've not learned yet) electric, or gas?
    – Ecnerwal
    Dec 2, 2021 at 14:37
  • @Ecnerwal My oven is electric and my hob is gas.
    – Dan
    Dec 2, 2021 at 20:58
  • @crip659 as far as I understand it was building regulation in the UK at some point in the past that walls had to have ventilation in them, but that is no longer the case.
    – Dan
    Dec 2, 2021 at 20:58

1 Answer 1


I would fill the entire cavity with firmly-packed fiberglass insulation in a plastic trash bag. This will serve to seal against airflow and insulate.

Alternatively, fit 2-4" of rigid foam (EPS) insulation toward the outside of the passage.

Then seal the exterior with whatever practical and pleasing manner seems appropriate so rainwater doesn't collect inside.

Once you're confident that you've accomplished that, optionally install a panel of 1/4" or 3/8" plywood or PVC over the opening, just to clean it up visually. You could use plastic anchors or construction adhesive. Obviously the latter would be permanent.

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