open fireplace throat size

[markymark2406]

I'm Shortly to be building an open fire place, I just want confirmation of how big the throat needs to be?

 

[theprinceofdarkness]

With out any knowledge I would say 1/2 to 2/3 of the grate area. This is to make sure that the flue sucks hard and the air which is not rising through the grate is being sucked from the room. This is to make sure that all the smoke goes up the flue. In your picture that sharp protruding edges on the back wall are not what you need, ready made fire backs have a nice smooth curves to allow the gases to flow smoothly, but I suspect this is more diagramatic drawing.
Frank

 

[markymark2406]

http://shop.vitcas.com/heat-resistant-concrete-fireback-16-530-p.asp

http://shop.vitcas.com/heat-resistant-fireback-lintel-16-657-p.asp

Yeah I know what you mean about the drawing, I'm purchasing as above links

Just need to know the min max distance from back to front lintel throat

 

[theprinceofdarkness]

Have you heard of Wikipedia? its an ace place. This is a link from it :-http://www.designingbuildings.co.uk/wiki/Flue_throat
Seems to have a lot of gen.
Frank