I'm appealing for some help from anyone who has had experience with flue's
going from a fire (in living room) up through into attic, and then
eventually through the roof. I have just had a fire fitted and the 'smoke
test' worked fine but after the install the flue is not 'pulling' or sucking
up enough and so the install is not complete. My fitter has tried fitting a
flue extension kit with unfortunately the same results. The fitter concede
I must have a blocked flue and recommended an electric fire or an electric
power-flue directly behind the fire in living room (which is noisy
I wasn't taking his opinion lightly and took my digital camera into the
attic and took a shot down the flue and the picture I got is posted here:
Now my query is that I do not know what to expect when looking down the flue
but it does appear that I have approx a third of what seems to be hollow
breeze block half way down the flue. Is this what I should expect to see or
is this perhaps causing my problem? Is this the way my flue was supposed to
be installed when the house was built or is it just a shoddy job?
The angle I have taken it at seems as if the block is hollow and my initial
thoughts are to hire some rods and try and break this off... however your
comments are very much valued before taking this a step further.
There is a simple formula that says for a fire to draw properly and not
smoke, it needs an aperture not more than 7 and preferably 5 or less
times the flue cross sectional area.
Not really gleaning anything useful from your photo sadly, I can't tell
if this is the case in your case.
Smokey fires are cured by raising the grate, or dropping a smokehood
down to reduce the aperture
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On Thu, 6 Nov 2003 00:04:00 -0000, "MR" <no-email-address> wrote:
It appears that you have a pre-cast concrete block flue or similar.
First things first,check the makers instructions for the fire and see
if it is suitable for a pre cast flue?
did you have a fire fitted to it and did it work ok before??
This is a common problem with this flue type and rodding out any
cement "snots" is a common fix. Access is a problem though. I have
done flue inspections using a remote camera in this sort of situation
A fan powered flue assistance device is probably a no in this
Something is bothering me about photo 1. It looks to me as if the inside
of the termination flue block slopes up and away from the front lip.
This suggests to me that the block is upside down !!. Can you actually
see *down* into the flue blocks below the termination one ?. I.e.
looking down towards the fire ?.
I have just come onto this thread. Oh Sh*t.
We have a really bad installation here:
1 Flexible liner used where rigid flue pipe should be used.
2 Terminal block on flue block system looks completely wrong - should be
45 degrees not vertical.
3 Flexible liner detached from flue block. (Though that may have been
done for the camera.)
Looks like at _minimum_ a doouble wall metal flue system needs to be put in,
also the top block block need removing and replacing with the correct
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at www.diyfaq.org.uk
Thanks for the updates guys. To answer some questions posed...
1) The picture pointing down the flue was taken by carefully sliding in my
digital camera into the hole you see in the attic (PIC 2 here:
http://tinyurl.com/tz1q ) This hole is a 90 degree angle so it goes in say
10-12inches or so then goes straight down. (like an upside down L ).
2) I have had several people comment onthe flexible metal tubing coming from
the hole and after reading up this SHOULD be a rigid flue pipe.
3) Liner was detatched from block - this was very loose as previously
mentioned and basically came out without any force! The blob of compound was
not secure at all.
I'm working with them to come out armed with the info and BS Standards/regs
quoted in this thread. I'll update you on what comes of the visit... your
further comments are still appreciated.
Thanks once again...
It is hard to tell what part of the flue this is. It looks like a pre-cast
one but not sure why you are able to take a pic 'down' the flue from inside
the attic. Does it have a soot box in there?
The most common cause for lack of draw is the wrong type of flue terminal on
top of the pot. What does yours look like?
Also, can you give me an idea of age of property?
Many thanks for all the posts and suggestions so far. I've been back in the
loft and taken some more pics that can be found here:
Pic 1 = This is the Flue 'hole' in the loft with the metal tubing that was
used with the flue extension kit.
Pic 2 = Now this is with metal tubing removed with a heavy blob of what
seems to be cement/putty on the end (this incidentally was loose and I have
not used ANY force at all to remove the tubing for the photo).
Pic 3 = This shows the flue in relation to the pitched roof.
Pic 4 = This is the fire we have had chosen and had installed.
Now I'm wondering from the posts whether the loose tubing in Pic 2 could be
posing a problem as this is not secured fully (flush/air-tight) to the hole
in the loft. Should this be in any way loose or am I correct in thinking it
should be flush/fully sealed to the exit hole?
Again your thoughts and comments are appreciated.
PS - The fire that was there previously seemed to work OK, but we have only
recently bought the house and the fire was one of the first things we
changed. The house is 30years old. And the flue did leave through a roof
tile at the utmost point of the roof, but then when the flue extension was
tried it was taken out around 1/2 way up the roof where a tile was cut etc.
I have a similar block type flue, and when I was discussing my heating
with a heating engineer, he asked me if the flue was connected to a
flexible pipe, or a dual skin solid pipe, mine is the latter, but he
said that if it had been a flexible pipe, he would have advised me not
to use it until it was replaced with a solid one. I did not ask why,
as it was not relevant in my case, but it seemed important to him.
That round hole leads up to a chimney/external vent I take it and you
can feel an up draft at that round opening? The other end of the pipe
then goes to the rectangular hole in your earlier photograph.
All these joints need to be gas tight otherwise the flue gases will
seep out. Flue gases aren't the best things for ones health...
There looks plenty of room in the box flue I'd be tempted to take that
single skin flexable liner right down to a register plate above the
fire or even to the flue outlet of the fire (if it has one) with just
the single joint into the round hole. In fact I'd probably investigate
getting the liner right up to the pot as well.
Dave. pam is missing e-mail
In my system, the flue is similar to a breeze block, with the centre
piece missing, and would be nowhere near wide enough to take the
I have just had another look at the original picture, and I do not
think the concrete is a blockage, merely an infill, at the side of the
block built flue.
On Thu, 6 Nov 2003 22:24:53 -0000, "MR" <no-email-address> wrote:
I presume your house is fairly modern and that it doesnt have a
chimney pot as such on the roof?
As i have said,it looks like you have a pre-cast concrete block flue
system. It might be terminated with a ridge terminal or a standard 5"
GC1 type terminal. The flexible liner is a joke,it should be twin
walled flue pipe rising as vertically as poss to the terminal with
pipe properly supported,clamped and joints taped to seal.
Check the manufacturers instructions for the fire,does it say it is
suitable for fitting to a pre cast concrete block flue.
Flue blocks and associated accesories should comply with BS 1289. The
cross sectional area should not be less than 16500mm 2 with a minimal
internal dimension of 90mm. Before 1986 these dimensions where csa
13000mm 2 and 63mm
Agreed - see www.dunbrik.co.uk - they make the flue block system.
You should never use single wall flexible pipe to connect flue
termination block to the ridge terminal, that is what twinwall (Selkirk)
is for. Flexible tube is only for lining existing brick chimneys.
Also, it is not allowed to have angles less than 45 degrees from the
vertical - and yours looks like it is horizontal, apart from having what
looks like a horridly bodged connection.
The smoke test failure is probably caused by the horizontal part of the
flue. What was there before ?.
My guess is that the fire that was fitted before was not of the 'living
flame' type. at least with flames that are open to the room, Possibly it
was a radiant fire or the flames were behind glass? Let me know.
Either way, it would be helpful to see what flue terminal you have fitted up
top as I suspect it is incorrect for the fire you are using. The Corgi
fitter who did the fire should have been able to advise you on this.
You are correct that ALL the joints must be gas tight. The idea is to get
as near as possible to a continuous and constant diameter flue running all
the way to the terminal, which of course, should be the correct type. In my
experience, about 80% of all older homes with gas fires have the wrong type
of terminal fitted. Even none at all would be better, but invites those
pesky pigeons to fall down after becoming intoxicated on the flue gases
whilst sitting on the pot for warmth.
Hope this helps a bit.
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