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

tusmaith

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.

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.

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

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."

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.