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description and dimensions of “throat”, see BS 8303: Part 1:1994

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  • 03-07-2013 9:04pm
    #1
    tusmaith
    Registered Users Posts: 42 ✭


    Hello There,
    I am trying to work out what size of a vent I need to install in a room where I am considering putting in an open fire in an extension I am building.
    I have checked TGD J of the Building Regulations and it states that "A ventilation opening (or openings) with a total free area of at least 50% of the appliance throat opening area (of which at least 6500 mm2 is permanent ventilation) shall be provided.
    I was considering installing a normal fireplace with a fireback and flue gatherer over it. I estimate that the throat in this scenario might be approx 150mm x 300mm (area 45,000mm2) so applying the logic in the building regulations I would need a vent of 22,500mm2 this would equate to 3 rytons brick vents????? surely this is not correct - I never see 3 vents installed in any room......
    That is why I am looking for the definition of "throat" as per BS8303, I know I could just go and buy the document, but it is £120 sterling or something like that....
    If the throat ends up being the flue dimension then it will have a big impact on the size of the vent required in the room.

    Any opinions / guidance would be appreciated.

    Thanks in advance.


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    #2
    Robbie.G
    Registered Users Posts: 1,884 ✭✭✭Robbie.G


    tusmaith wrote: »
    Hello There,
    I am trying to work out what size of a vent I need to install in a room where I am considering putting in an open fire in an extension I am building.
    I have checked TGD J of the Building Regulations and it states that "A ventilation opening (or openings) with a total free area of at least 50% of the appliance throat opening area (of which at least 6500 mm2 is permanent ventilation) shall be provided.
    I was considering installing a normal fireplace with a fireback and flue gatherer over it. I estimate that the throat in this scenario might be approx 150mm x 300mm (area 45,000mm2) so applying the logic in the building regulations I would need a vent of 22,500mm2 this would equate to 3 rytons brick vents????? surely this is not correct - I never see 3 vents installed in any room......
    That is why I am looking for the definition of "throat" as per BS8303, I know I could just go and buy the document, but it is £120 sterling or something like that....
    If the throat ends up being the flue dimension then it will have a big impact on the size of the vent required in the room.

    Any opinions / guidance would be appreciated.

    Thanks in advance.
    Someone will probly correct me but a vent size of 150mm should be adequate for the fire.Is there any other vent currently fitted in the room.


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    #3
    Robbie.G
    Registered Users Posts: 1,884 ✭✭✭Robbie.G


    Robbie.G wrote: »
    Someone will probly correct me but a vent size of 150mm should be adequate for the fire.Is there any other vent currently fitted in the room.

    There is some info here that might help
    http://www.soliftec.com/airsupply.htm


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    #4
    tusmaith
    Registered Users Posts: 42 ✭tusmaith


    Hi Robbie,
    Thanks for your replies!
    That is a brilliant website!!!!
    I think that getting the definition of "throat" in the BS is key to getting the actual requirement.
    I note that the website states that Open Fires have a different, often very large, air requirement."


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    #5
    jiggerypokery
    Closed Accounts Posts: 53 ✭✭jiggerypokery


    Your definition of the throat area is correct - 3 quarters of the width of the fireplace multiplied by the depth. But as you say when have you seen 3 vents in a room.


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