Internal wall vents

[Picket Fence]

I have a 3 bed semi built in the 1930s. In each bedroom and the bathroom there is a vent (approx 150mm x 200mm) in the upper corner of the wall.

What are these for? Do they still serve any purpose?
Can I block them? I have one that is quite drafty particularly when we have a cold northerly wind. If cold gets in throught the vent then warmth must be getting out. Wasteful.

An insulation company has checked and told me I already have cavity insulation - I'm not 100% convinced. Should insulation eliminate the draft or do the vents go right through the cavity and external wall? I can see nothing on the external walls. Mine and all similar neighbouring houses are pebbledashed - I assume this was done when they were built.

Any thoughts appreciated.

 

[AndersonC]

They are present in a couple of rooms in our house but have air bricks in coincident positions on the outside wall. I've had to brick one up as I had a boiler flue situated in it's vicinity. I guess they were put in simply for ventilation, but we have windows open a lot of the time so the vents are largely useless to us.

 

[JohnD]

You can fit a Hit and Miss vent. Cheap, easy, and can be opened or closed according to your whim.

Theu should have ducts so the presence of cavity insulation is irrelevant. Insulation is not supposed to block airbricks or ventilators. Poke a bit of wire in to see where it vents to. Maybe some dummy blocked up the outsides.

You can use the one in the bathroom for your extractor fan (assuming it vents outside through a duct)