How to block (cover) large air vent in bedroom

[confounder]

Hi All,

We live in a 1930's semi-detached house with 3 bedrooms. The box room has an air vent around 20cm x 20cm with a grille on the outside and a plastic cover purchased from B&Q on the inside.

We are looking to permanently cover this air vent since it makes the room very cold.

What risks are involved if we cover this up? Also, what is the best way to do this? I guess expanding foam probably won't work for an air vent of this size.

Thank you in advance for any advice.

 

[PrenticeBoyofDerry]

You risk condensation becoming present in the bedroom, that is likely why it was installed in the first place.
You can buy internal vent plates that can be opened and shut.
Does the one you have linked to allow you to do this, does it slide left-right/right-left?

 

[confounder]

Yes, it allows the shutters to slide left and right (open and close). However, the draft through the vent is still quite strong.

I agree that condensation will be an issue since even with the air vent, the windows steam up every now and then.

What are the options in terms of blocking up the air vent?

 

[PrenticeBoyofDerry]

Brick up and plaster.
You could tape a plastic bag/polythene sheet over the vent as a temp measure, just to see how the room reacts without ventilation.
You may find that you start not only condensation on windows but also behind furniture that is up against walls.
Is the area above insulated and are the windows double glazed and in good condition?

 

[confounder]

The windows are double glazed and in very good condition. However, the house is on the small size and windows tend to condense up.

Loft is insulated. I don't recognise any other insulation in the box room which has the air vent.

Thanks.

 

[StephenW]

I have a similar sized vent in my kitchen to supply sufficient air for the floor-standing gas boiler. Now that the boiler has been removed (replacement now in the garage), I have stuffed up the vent with bubble wrap (full thickness of the wall) and then put gaffer tape on the inside of the inner cover and screwed it back on. Result - a much warmer kitchen with no "waterfall" of icy air. Other ventilation is still sufficient to avoid condensation issues.

 

[foxhole]

I have a similar sized vent in my kitchen to supply sufficient air for the floor-standing gas boiler. Now that the boiler has been removed (replacement now in the garage), I have stuffed up the vent with bubble wrap (full thickness of the wall) and then put gaffer tape on the inside of the inner cover and screwed it back on. Result - a much warmer kitchen with no "waterfall" of icy air. Other ventilation is still sufficient to avoid condensation issues.

Hope you don't have a gas stove.

 

[garyo]

Hope you don't have a gas stove.

So - a genuine question - how do these modern air tight barret homes manage with gas stoves? Come to think of it, how do their extractor hoods ever manage to suck anything out when they're fighting against such a well sealed envelope?

 

[StephenW]

Hope you don't have a gas stove.

Thanks for raising the issue, I should have mentiioned it as a caution.
Yes, I do have a gas cooker in said kitchen but the ventilation and extraction is still within specifications. It was just the big vent which provided the extra fresh air needed for the boiler which I blocked up.

 

[foxhole]

Hope you don't have a gas stove.

So - a genuine question - how do these modern air tight barret homes manage with gas stoves? Come to think of it, how do their extractor hoods ever manage to suck anything out when they're fighting against such a well sealed envelope?

No one builds air tight homes with no ventilation.

 

[Perry525]

Water vapour from breathing and sweating is always a problem in a bedroom with little heating.
Having written that, there is no point in having a hole as large as you describe, as this is overkill once you take the wind into consideration.

Water vapour is programmed to always move to the nearest cold surface, this works OK in most bedrooms as once the curtains are drawn or the blinds closed the air temperature behind the curtain or blind drops and all the water vapour moves to the window and condenses, where it can be mopped up.

The cheapest controllable way to deal with water vapour is to vent it to the outside, where it is usually drier, by opening a window for a few minutes. If it is cold outside, then use a dehumidifier.

From 2016 all new houses will be built to Passive house standards (as near to being air tight as they can be) that will come with mechanical ventilation and the use of heat exchangers to save money.

I recommend that you avoid using anything thin where the inside temperature will be below the dew point and will result in condensation, go for a plug of polystyrene or similar at least three inches thick, this will ensure the indoor surface remains warm and above the dew point.