Restoring class 1 chimney flue - thermalite blocks?

[woodster]

Hi,

I want to restore a chimney flue which was broken into in the first floor bedroom where a chest of drawers had been inset into the chimney breast. My initial thought was to use a good quality brick, but a friend has suggested using thermalite blocks for a quicker and easier job. Can I rely on these to keep the flue intact?

I will be putting a multistove in the downstairs living room so at the point where the flue is restored upstairs, it will have the usual output from a stove flue, but there will be no direct heat from the upstairs fireplace which I also intend to brick up. Bearing in mind I have no building experience.

Thank you

 

[bludger]

Hello Woodster,

The chimney stack is often an integral and vital part of the building structure. I'd feel happier, if this is the case and it was mine, to have bricks in it rather than thermalite blocks.

You also ought to check whether or not your chimney will need lining. Many modern stoves need a smaller flue than the normal brick chimney to get a good enough draught to operate efficiently.

Select your stove and its instructions will tell you about the flue size needed.

Bludger

 

[woodster]

Thanks Bludger,

You have confirmed my suspicion that I need to use brick. I am also going to have a chimney liner installed for peace of mind.

Cheers

 

[bludger]

Hi Woodster

They are wise decisions. If a chimney doesn't draw properly, the products of combustion (tars and gases) condense onto the brickwork because it isn't hot enough to take the smoke right out of the chimney. The condensed stuff can leach through the brick joints and spoil decorations and also contributes substantially to the danger of a chimney fire.

Best,

Bludger

 

[woodster]

Thanks Bludger,

would you advise insulating the liner then? One shop has told me this is essential for the life of the liner, yet other shops don't seem to thinkit matters???

 

[RigidRaider]

Insulating around the liner with that inert volcanic ash material (don't remember the name) will give you the most efficient flue and a roaring fire. With this quality of updraft you're well advised to go for the controllability of a multi-fuel stove.

However if it's a class 1 flue you might not need a liner. We had a lined/insulated flue in a previous house and the stove (Douvre) roared like a dragon from the moment you lit it. In our present house we have the very same stove but unlined class 1 flue, it takes a while longer to get into its stride but once there's a column of rising hot gases it performs just fine. The lining is pricey, around £50 a metre.

You really need a good chimney sweep to advise you on this - don't go for the trendy high street stove shops unless they are also proper sweeps/chimney experts.

I see you're in Cumbria. I strongly recommend Ian at Acorn Chimeys in Burnley though he is a busy man.

 

[woodster]

Yes, we were quoted £50 per meter for lining. I asked the shop owner what grade the lining was and he said it was 316 grade.

So why is it a simple google search can lead me to companies selling the same grade liner for £16 per meter? Is it different stuff?

example:
http://www.hotline-chimneys.co.uk/liner_class1_316_150mm.htm

It may be cheaper to buy all the equipment online as indeed the stove itself, and get a qualified fitter for the installation.

 

[RigidRaider]

Hmmm..... that's interesting, isn't it! Looks like the very same stuff.

The first step is to find a good chimney specialist. If you do need a liner it's not just a question of stuffing it down, you might find the flue obstructed with lumps of mortar or a bend. There's the chimney pot and cowl to consider, as well as the plate up inside the fireplace, which acts as a support and termination for the flue and locates the stove pipe. (Isn't this called the register plate?) Then you need to make provision for sweeping, which means a rodding port in an accessible place, properly fixed with stainless screws, as well as ensuring no exposed steel edges on the stove pipe to rust in the flue gases.

Have you found a log supplier? What about storage? You need to get the wood delivered now if it's to be anywhere near ready for burning this autumn, even now is too late really if the wood is green. We built a lean-to shelter on the side of the house with a long narrow sloping roof and some euro-pallets from work, on which we stack the logs. Our leftover logs from last winter are now burning fantastically while the new delivery is drying out. Make sure the log bloke doesn't give you too much yew or cypress as these produce nasty tars, which are bad news.