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Removal of Cast Iron Chimney Flue & Fitted Fireplace From inside a BISF House.

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Removal of Cast Iron Flue Pipe & Fireplace From a BISF House by Member Doug.

(Admin note: BISF House member Doug has kindly put together the following excellent post showing the complete process of a cast iron flue removal inside a typical BISF hous.e. In creating this post and taking the time to record the entire process, Doug hopes that he can share his experience with other members and more importantly he hopes that it may be a useful resource for others. Our sincere thanks to Doug for this valuable contribution)

Hello everyone here at BISF House.

I recently removed the cast iron flue and fireplace from a BISF house and thought that I would share it with you all. This post relates to BISF Houses where the fireplace is fitted to wall between the living & dining rooms.

Before starting there are few safety points to bear in mind.

  • You will need a 6-12 inch cast chain cutter. This is a heavy item and will require 2 persons to complete the job.
  • Always wear safety glasses and gloves and if possible, steel toecap shoes just in case.
  • Always wear a high quality dust mask and wherever possible always dampen down any insulation material that may surround the flue with a spray bottle of water. Although not prescribed, we can never rule out the possibility that installers may have used asbestos insulation in some cases. If you suspect the presence of asbestos do not undertake this work until the material has been correctly tested by an approved body.
  • Always wear a disposable worksuit with hood. This can be an extremely dusty job.
  • Never use an angle grinder as sparks can easily ignite insulation or travel under floorboards, causing fire.
  • A strong working platform and extra lighting in the roof would also be a good idea.
  • Don't remove any of the supporting frames yet as it contains the pipe clamps which keeps the flue pipe in place. You can work around the frame without any problem.E
  • Ensure that any and all pipework leading into or out of the fireplace are disconnected or safely capped off away from the work area.
  • All gas pipes should be diconnected by a Gorgi registered plumber.
  • Water pipes if present should also be removed and capped if of no further use.
  • Always turn the gas off at the mains prior to undertaking any work as there may be hidden gas pipes that you are not aware of.

Originally, BISF houses were fitted with open coal fires that heated a small sealed back boiler that was situated behind the main firebox. This was a basic water or oil filled unit that heated radiators in the house. If still present, the box and pipework should be capped and carefully removed.

Admin Update: There have been a number of safety incidents including one fatality where old solid fuel back boilers have exploded due to the recommisioning of old coal fires. Such events are not specific to BISF Houses. Please see

In the 1980's many BISF properties were fitted with Baxi Bermuda gas fires with integrated backboiler. The back boiler was positioned inside the firebox, directly behind the fire itself.
This fire is fairly straightforward to remove once the gas feed has been safely disconnected. The front of the gas fire can pulled forward and carefully separated from the independant back boiler. You may find several mounting screws that need to be removed and possibly a pipe connection but the two parts of the fire and boiler should seperate.

First, completely remove the existing fireplace surround. The surround is usually constructed from large slabs which should be pretty easy to break up using a lump hammer or similar. It would be wise to dismantle the top mantle slab first. One stripped away you should be left with the concrete firebox surround. (Images 1 & 2) and also the boxing from around flue in the front bedroom.  ( Images 3 & 4) Note the flared joint located 2 thirds up in the bedroom. (Image 5)

Firstly remove the fire place surround

Side view of fireplace

First, remove the fire place surround (Images 1 & 2) and also the boxing from around flue in the front bedroom.  ( Images 3 & 4) Note the flared joint located 2 thirds up in the bedroom. (Image 5)

 Starting in the attic the below image shows the cast iron flue tube passing through the ceiling plate as it starts its journey down through the house via the first floor ceiling (Image 6)

The next image shows the flue at the point where it exits the roof toward the chimney. You can see at this point that it is clamped into place by a surrounding bracket. (Image 7)

Loft Support

As I won't be disturbing the top part of the flue, my first cut will be just under this top clamp, The chain cutter is feed around the tube and locked into position then slid up to the first cut. (Image 8)

Pipe Cutter

 The cutter works on a ratchet system which slowly tightens the chain until it cracks the tube, it's quite noisy and a bit scary. Also a note as there was a gas back boiler and fire a liner has been fed through the tube as this needs to be removed first I made 2 cuts. (Image 9)

Cut Pipe

Then using a reciprocating saw through the small gap I cut through the liner then removed the small flue section before removing the liner by pulling down and out from the lounge fireplace. I found this the dirtiest job so be warned lots of soot rust etc. came down with the liner. (Images 10 & 11)

A manageable flue section was cut lower down near the ceiling plate. (Images 12 & 13)

*CAUTION* if you cut off a flue section which is unsupported the top cut section jumps upwards due to the force of the cut, BE PREPARED.

My next cut was in the bedroom tight to the ceiling pic 1 then half way above floor level Pic 2 then at floor level pic 3. You could cut larger sections but I opted to keep small sections. (Images 14, 15 &16)

One more cut in the lounge third of the way from the ceiling the cut section being removed from above. The last section which sits in a plate on top of the fire box you can wriggle until its lose and tilt back to lift out. (Image 17)

Flue Frame

You are now left with the frame which is bolted together in 4 sections then another 4 sections in the bedroom bolted to the downstairs frame. (Images 18 & 19)

There are wood batons nailed in the corner angles to which the plasterboard was nailed too, you can pull the nails out to remove the baton to enable to access the frame bolts. This is straight forward but a fiddly job. The bottom of the frame is cast into the concrete plinth I cut the frame at floor level to enable me to remove it as won't be taking up the concrete plinth just yet. Once all the frame has been removed the concrete fire box can be removed in sections although a little heavy easily removed. (Image 20)


Then making good the ceilings and floors is the last job but as I'm about to undertake a major refurbishment of the lounge the making good will be part of that project. (Image 21)

My local scrap merchant took all the scrap away at no cost to me he even loaded it himself!

Hope this is helpful any questions just ask

Topic starter Posted : 1:09 am
race liked
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Hi I'm in the process of removing my flue but I carnt find anyone with a pipe cutter larger then 6". And would love to no where you hired yours thanks

Posted : 4:47 pm
Grangey (Senior Member)
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Trust me, it may be somewhat messier, but I found using a sledgehammer far quicker. I too couldnt find pipe cutters big enough so also tried a disk cutter, it takes ages. Give it some very hard smacks from the top down and once it starts cracking its easy enough

Posted : 7:31 pm
Member Admin

Hello Dan
I have to go with Grangey on that too, albeit not the safest way of removal.
I used a sledge hammer to remove mine and it was certainly a chore and ear defenders and goggles are a must. It breaks into segments but once it has started to crack it was much easier. It's getting the first crack in the cast iron that's the hardest part.
It's a bit like smashing up a large cast iron bath only much thicker. Just make if your working in the loft that you have some floor covering or temporary boards in place to prevent large pieces falling through the ceiling board. If working in the bedroom or living room try to cover any windows with tarpaulin to prevent any flying bits from hitting the glass.
Also make sure you wear a mask and disposable boiler suit if you have to remove any insulation from around the pipe as there is some debate that it may or may not contain asbestos fibres. I wrapped mine with cling film to help keep the fibres in place and also used a water spray bottle to keep them damp and prevent fibres from flying round.
It is much safer to use a pipe cutter though and due to safety it is the only method that we can recommend. It makes the sections far easier to handle with less likelihood of large pieces dropping down.
When working from the living room as I did, once the lower section is cracked, you can thin chip away fairly easily until the lower section loosens up and it can sometimes be pulled out in one piece. The upper section should remain in place due to clamps that hold it secure and one is visible in the loft but you should not always rely on these being secure and you should check they are tight before you start.
The worse case scenario is that once the lower pipe has been smashed. the upper section could drop down if not held securely and believe me it is heavy.
Make sure that you have a clear working area and are able to move away quickly if you think it may drop.
Once again though I must stress that using an industrial pipe cutter which can be hired from certain hire shops or drainage companies is the only method we can endorse. We take no liability for any of the suggestions given as they are only personal views.
At what stage are you at now, have you stripped back the fireplace and boxing?

Posted : 12:30 pm
Member Admin

A quick Google search for industrial chain pipe cutter hire list Brandonhire who have a 19" cutter but if I am honest I cannot recall the diameter of the pipe.
In my case I also used a large angle grinder with a special high performance blade that cuts wood, metal, stone etc that was ridged and made of steel rather than normal grinding blades that wear down very quickly when faced with thick cast iron.

Posted : 12:39 pm
Member Registered

It's out!!!!! went with the sledgehammer wasn't as bad as I thought thanks everyone. Trying to remove the framework now any tips? It seems to be held in place just above the living room ceiling and won't come free?

Posted : 2:54 pm
Grangey (Senior Member)
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For that, its far easier using an angle grinder tbh

Posted : 12:04 pm
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I took out my whole flue yesterday which in all honesty was unplanned as I only intended to take out the ground floor and first floor sections and leave the attic section. This article was really useful.

Had our back boiler removed which allowed us the opportunity to open up the living room more and get rid of the fireplace.

I am about to start a refurb/ decoration of our lounge. Bisf houses are brilliant even as a beginner DIY'er I have enjoyed pulling down walls and re configuring parts of the house. Will upload photos of the things we have done soon .

Thanks for everyone else posting articles like this one which have helped me so much

Dave and Nic

Posted : 2:55 am
Member Admin

Hi Dave & Nic
Glad you decided to take the plunge, it will be well worth the effort in the end. :0)
Which method did you use to break up the flue?
Once started it's pretty much plain sailing although it does take a fair bit of hard graft. Don't forget you can still install a new gas fire if you ever feel the need as there are many flueless systems available that don't require a flue, although you do need to create a new air gap, but that's another story.
Have you removed the chimney cowl from the top of the roof covering otherwise known as the chimney pot on a traditional house?
Keep us updated and well done with your project

Posted : 11:55 am
Ed (Senior Member)
Member Registered

We have just had our back boiler removed and I'm planning on taking out the flue, starting in the loft and bedroom. I have noticed though that it doesn't seem to be made out of cast iron but looks like steel to me. I used a hacksaw to cut into it as a test. Cast iron wouldn't do that.

Obviously cast iron and steel would be removed in different ways. Steel can be cut more easily than cast iron but can't be broken/smashed. Were different types of flues used in BISF houses or is this just a case of mistaken identity?




Posted : 9:11 am
Ed (Senior Member)
Member Registered

Hi all,

I've started removing our flue the other day. I couldn't find a chain cutter locally large enough to hire, so I have been using an angle grinder instead and done it in a slightly different way from Doug.

First of all I cut the flue off in in the loft as close to the roof clamp as possible and then again about half way down to the loft floor, to keep the size of the pieces manageable. As I didn't have a special saw to cut through the flexible flue liner inside, I used the angle grinder to cut this section of flue in half length ways. Once so exposed the liner was very easy to cut with the angle grinder. Then I cut the next section off the loft floor. The pipe is big enough that when you cut fully through it doesn't risk toppling over and injuring you, it just sits on the part below, which is an advantage of the angle grinder over a chain cutter. Also the flexible flue liner helps keep it in place - I found I had to lift the cut section up off the flue liner and then cut the liner.

I found it was better to dismantle the steel frame around the flue in the bedroom first so it was easier to cut it. Even so it wasn't possible to get the angle right behind it in the corner between the wall and cupboard so there was a bit at the back of the flue that remained uncut, but if you free the flue first by taking off the clamps it breaks off fairly easily if you push against it.

I found the flue liner was too tight to pull out in one piece as it's quite a snug fit and the inside of the cast iron flue is very rough.

I haven't yet got down to floor level in the bedroom. The next step will be to repeat the process in the living room. I'm still deciding whether just to gain the extra space in the bedroom where the flue has come out, or to build another cupboard in its place for extra storage up against the end of the existing built-in cupboards.


Posted : 9:08 pm
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