On Sat, 10 Nov 2012 23:08:31 +0000 (GMT), "Dave Liquorice"
wrote:

On Sat, 10 Nov 2012 18:18:44 -0000, Lawrence wrote:

Can you not fit the largest flue and them put a spigot plate at the
bottom to match your stove?

You can as in physically but I don't think the BCO would like it as it is
probably against the installation instructions of the stove.

I don't think he can complain as long as it is greater than 150mm id

A large flue will slow down the flow of gases, the longer they take the
cooler they get and more chance of tar/soot deposition in the flue.

Yes but to some extent this will depend on heat loss to the sides, if
the flue is insulated or the brickwork has reached a constant
temperature then there may not be a lot of difference. I imagine many
brick chimney are 9" and would still pass.

It will also affect the draw. I can't decide if it won't draw enough,

The draw is dependent on the buoyancy of the air in the column, if
it's cooler then less draw.

I still cannot figure why a sophisticated bit of kit like a modern gas
boiler, which is fueled by a gas that is readily combustible, has a
fan, yet a wood fire which has a low cv fuel which is difficult to
cleanly burn and would benefit from the turbulence and air control is
resisted.

AJH