Capitol wrote:

The Natural Philosopher wrote in message ...

Rick Dipper wrote:


I had this issue, the opening was too tall, the local fire shop sole me a

small "hood" to fit in the top or the opening.


Ok, I hjad this problem in SPADES when the dumb builder built my

inglenooks.

There is a page on the web that I discovered that covers this all in

detail.

There are a few salient points you need to know.

The most important is that the fire APERTURE - if you like the area
bounded by the grate, the sides of the fire and the lintel over teh top
of it should be no more than 5, or at most 7 times the cross sectional
area of the flue. Any more than this and the velocity of air being drawn
into the fire will not be enough to suck stray smoke into the fire etc etc.


I'm not disagreeing with this comment, but it is possible to work with
aperture ratios approaching 14 if the entry to the chimney is funnelled.


I would agree with that to the extent that muy smike hoods are running
on estimated 10:1 ratio and work fairly well. They don't 'draw' like a
coal fire throtled down does though. I suspect my 5-7:1 was a ratio for
open hearh coal that needs a better draught.


Most standard fire places use an angled restictor throat at the entry to the
chimney, to produce a pressure change which aids gas flow. Sorry, I can't
remember all the details, perhaps someone else can enlighten us. When I
researched the problem of building fireplaces, I found that all the
experienced fireplace experts, said "Try it and see if it works!, but allow
for a fanned flue if it doesn't!!"


Those are hopeless. The noise is incredible. They are the open fire
equivalent to Saniflo.


I'd agree however that some form of a reduction in aperture is probably the
easiest solution. It's probably worth asking a few questions of an
experienced fireplace showroom, they may have an off the shelf solution for
a few pounds.


Few hundred pounds. They know bugger all as well, I tried. In fact I am
probably the nearest thing to an expert that exists. And I know next to
bugger all. You can get pre-desined coal fireplaces that will sork whjen
slotted into standard flues, but no one build wod burning firepalces any
more. After a struggle, mine are beginning to perform well - not just
adequately, but well - and the experience is as I summarised.

The key is reducing fireplace aperture by raising the grate, or fitting
a smoke hood.

Insofar as smoking is concerned. You can fine tune that by throttling
the flue in a smooth choke type design, that accelerates airflow around
the aperture top, but too much throttling will reduce flow rates too much.




Regards
Capitol