Kitchen vent - to block or not, and how?

[Angilion]

Alternative title by Neil the Hippy: There's a hole in my wall (and it's letting out money).

I've always known that my kitchen is considerably colder than the adjacent living room, but I'd idly assumed that it was down to a combination of two external doors, a large single pane window and being an extension.

While cleaning out the gutter one day, I happened to be at the right angle to be able to see through the wall into the kitchen. Somehow, I had avoided paying any attention to a fairly large hole in the wall, covered by slatted vents each side. The inside is in an alcove where the boiler is, high on the wall, almost flat to the wall and painted the same colour as the wall, so it's not immediately obvious.

I'm almost sure that it's a vent for a different type of heating from long ago, because I'm almost sure that for years boilers have been sealed from the room and don't need external venting on the wall next to the boiler. The boiler has its own venting to outside - this is a hole in the wall about a foot to the side of the boiler, not connected to it at all.

So unless someone who knows something I don't says the extra vent is a useful safety measure, I'm going to block it up. What would be the best way to do it? I was going to use that expanding spray foam filler, which should be easy, but I'm thinking that's probably not much good for thermal insulation.

 

[Angilion]

I would advise that you get a heating engineer to take a look before you go blocking up random vents in your house, have you got someone that services your boiler that can give you advice?

Yes, so I asked them. Their opinion is that the vent has nothing to do with the current boiler - it's a standard modern condensing boiler that's a sealed (from the room - it vents to the outside through the wall) unit, has no need for external vents in the room and couldn't make any use of them anyway.

So...what's the best thing to fill it with? I'm not sure if it's single brick or cavity wall...I think it's cavity wall but I've no idea how to check. I had cavity wall insulation put in about 10 years ago, but I'm not entirely sure if that included the kitchen extension or was just the main house. I can't check for external drill holes because the whole house is cladded with insulation. That foam filler would be easy, but I'm thinking that it's probably next to damn all use for thermal insulation.

Here's something interesting:

In older brick homes, air vents were placed in walls to let moisture move out of the space between the exterior and interior walls so that mould would not grow there. Modern moisture barriers and sealants have largely replaced this function.

From http://www.ehow.co.uk/facts_7455505_air-vents-walls-older-homes_.html

My house was built ~1900, but the kitchen extension is newer (no idea when that was built - it's in the surveyor's report somewhere, but I forget). Long enough ago for the bricks to look as old as those in the original house, anyway. So I doubt if there's anything modern in its construction. Maybe I do need the venting not for the boiler but for the moisture. I have no idea if the above statement is true.

Aha, here's a possible answer from a forum about it:

Have filled in the inside vents using patching plaster. A year later no problems. Air can still circulate through the cavity between the inside and outside walls via the external vents and I don't plan to block these.

http://forums.whirlpool.net.au/archive/1897762

That looks like the best bet. Although if there is a cavity then it's filled with insulation anyway. I'm still not sure. Although one thing I am sure about after reading a few forums - don't use expanding foam. Time and time again, I've seen people saying that they tried it and it was rubbish.

 

[Angilion]

Or indeed the house.

OP if you're living in a building with lime mortar/ render I would seriously advise you seek professional advice before blocking vents. Old properties needed to breathe in order to prevent damp issues.

I've no idea what the mortar is made of, but the main house is much older than the kitchen and the main house doesn't have vents in the walls. There's a problem with damp in one bottom corner of one room, but I've had that looked at by two builders and they both said it's due to the back yard being higher than the house and the only real fix would be to lower the back yard (rather impractical at best).

I was in two minds about the vent when I started this thread, but now I'm in at least three