Flues

On the plans from the structural engineer the size of the flue pipes to each of the fireplaces is shown as 200mm diameter. To get a good draw on a fire the rule of thumb is that the fireplace opening should be 8 or 9 times the area of the narrowest part of the flue.

Using some schoolboy maths (pi-r-squared) gives a flue area of 31416 mm2 which, using the rule of thumb translates to a fireplace area between 251328 and 282744 mm2.

Back to the drawings, the fireplaces are all specified as 500mm x 550mm which is an area of 275000 mm2. So far so good - this is slap between the two limits from the flue size. However, a fireplace of 500 x 550 mm is not very big - less that 2 feet square in "old money". This certainly seems too small for a room that is over 6 x 6 m. I realise, of course, that the fireplace feature can be much bigger than the actual opening, but even so, what do I do if I want an inglenook, for example ?

I tried to find suppliers of flue pipes larger than this, but it seemed nothing larger is available. I asked the builder and he said he would speak to his supplier, but it doesn't seem very hopefull. One solution, of course, is to use a wood burning stove. It doesn't matter how big the opening is then, because the smoke-stack is "plumbed in" to the chimney. This is certainly what we shall do in the basement, but I have to confess to a hankering for a "propoer" open fire in the living room. However, I want it to be a decent size !

Does anybody have any ideas as to how this problem is usually solved ? Does the builder have to hand-craft a flue size any larger than the 200mm standard or are there specialist suppliers ?