Wall air vent - anti-draught baffle?

A common problem, I know. The two 9"x 9" air vents in our lounge - necessary because of the open gas fire - allow through a blast of cold air in windy weather. I vaguely remember hearing about some kind of baffle, fitted within the cavity wall, which allows the air through but prevents draughts. However I can't locate anything like this. Did I imagine it?
Richard. http://www.rtrussell.co.uk / To reply by email change 'news' to my forename.
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I can't imagine what could allow ventilation (the flow of air) yet prevent draughts (a flow of air - but not desirable). The best idea might be to duct the vent to nearer the fire so it isn't drawing the air across the floor and making your feet cold.
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Isn't 'ventilation' related to the volume of air, but 'draughts' related (primarily) to the velocity of air?
Richard. http://www.rtrussell.co.uk / To reply by email change 'news' to my forename.
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Richard Russell says...

Interesting. I've got the same problem with a vent which allows fresh air into a downstairs room which otherwise suffers from damp problems. However in windy weather it doesn't half blow through. It's noisy too. Perhaps some glass fibre insulation stuffed between the inner and outer vent would stop the wind blowing through but still allow an adequate air flow? Or would it just get soggy and block the air completely?
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On Sat, 22 Mar 2008 16:12:30 +0100, David in Normandy

Or it might just blow glass fibre threads into the room.
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On Sat, 22 Mar 2008 14:04:39 GMT, John wrote:

You make the path longer and bendier, thus slowing down the (forced) draught but still allowing the (unforced) ventilation. With ventilation for a fire one has to do this without reducing the effective cross sectional area of the ventilation...
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wrote:

How do you measure that area? Is it the full area of the two 9" x 9" vents (about 0.1 sq.m. total) or something less because of the 'attenuation' of the inside grilles and the outside louvres? It would be possible, surely, to construct some kind of internal 'labyrinth' which would create the "longer and bendier" path without reducing the cross-sectional area below that of the holes in the grille.
Richard. http://www.rtrussell.co.uk / To reply by email change 'news' to my forename.
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Evidently I'm not the first to have the idea:
http://www.freshpatents.com/Vent-structure-forcing-a-z-pattern-air-flow-dt20071129ptan20070275652.php
Richard. http://www.rtrussell.co.uk / To reply by email change 'news' to my forename.
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Are the vents diametrically opposite? Could equivalent sized vents be installed nearer to the fire to reduce the effect of the draught? Have you got a solid floor - or is it a wooden one with space under it?
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The vents are either side of the fireplace.

They're about as near to the fire as they can reasonably be, given the width of the fireplace and the external chimney stack.

Solid, with underfloor heating.
At present a pair of loudspeakers are placed immediately in front of the vents (with a largish gap), which do help reduce draughts but do nothing for the dreadful howling noise!
Richard. http://www.rtrussell.co.uk / To reply by email change 'news' to my forename.
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