Cob Chimney?

[Frank Duffy]

In message <199804262327.SAA24447 at bminet.bminet.com>, Chuck Learned
<clearned at bminet.com> writes
>I have the same interest as Mike in building an exposed Chimney. Mike I am
>currious why you
>have two flue's. I know nothing but it would seem that with all that good
>air circulation and linseed
>oil that the chimney would ok. I look forward to this reply. Also I am
>wondering how high above
>the roof the chimney needs to be?
>
I may be able to offer specialist advice here from my professional
background. I lurk out of personal interest and read most of the
postings.  However chimneys are my game!

There are a couple of points that spring to mind in relation to cob
constructed chimneys.  The main problem could be moisture from the
inside rather than from the outside.  The biggest problem will be caused
when the chimney serves a stove, cooker or other closed appliance.
Modern appliances are far more efficient than they used to be.  In days
gone by when the chimney probably served an open fire then large amounts
of air would have also been drawn into the flue.  This helps to keep the
flue walls dry.


Modern appliances have high flue gas temperatures though a smaller flue
gas volume.  So you have less actual heat put into the chimney.  This
means that condensation occurs in the flue and can lead to liquid
running down the inside or soaking in and destroying the cob.

The other problem could be that if the flue is taking the higher
temperatures from appliances these days then the cob itself may not
last.  A wood burning stove can have flue gases leaving it at 550C
(1000F)

-- 

Frank Duffy
Personal email to                  frank at chimney.demon.co.uk

at work...
ISOKERN - the safety chimney       fduffy at isokern.co.uk
                                   http://www.isokern.co.uk