Chimney Question

[Ed_MK]

Hi all

 

We are at the stage in our build, where the brickie is due ..and of course we are talking chimneys!

now its a Potton build and has an end/external chimney detail running up one side to the apex (see pic of very similar one built a few years ago)

 

I do remember the BCO asking about chimney detail, I was also told by someone "not too worry" as we are only fitting a 
gas "look-a-like" stove thingy ...(see other pic) ....

 

I took this to mean that we would not need all those liner tubes and stuff i "presume" are for REAL fires ...and that would only need to
stick one of those flexible fat tinfoil snake pipes up the brickwork to the top 

 

...or am i getting it wrong here? ...its been KNOWN !!

 

I have seen these flue "kits" online and they are like £700 and talk about vermiculite? and filling stuff with cement and the like.

talk of putting "starters" in (sigh) ....I mean don't get me wrong ...I dont want to die from co2 !! ..so i want it to be right.

I just dont want to have it to Power station spec and standards if i dont need to 

 

 

[nod]

We have a very simalar chimney 

and will instal a wood burner 

We build in a liner kit and don’t intend using a flexible pipe

The chimney kit was designed through our local plumbers merchants Bends etc and cost about £400 

The only thing that BC insisted on was that it was built in small stages and back filled around the liner with a 7-1 sharp sand mix to allow expanding and contracting 

Perfectly smooth joints and loads of photos

[nod]

21 minutes ago, nod said:

We have a very simalar chimney 

and will instal a wood burner 

We build in a liner kit and don’t intend using a flexible pipe

The chimney kit was designed through our local plumbers merchants Bends etc and cost about £400 

The only thing that BC insisted on was that it was built in small stages and back filled around the liner with a 7-1 sharp sand mix to allow expanding and contracting 

Perfectly smooth joints and loads of photos

[dpmiller]

Are those concrete flue pipes rather than clay?

[PeterW]

They look like Dunbrik liners. I’ve used them, should have some sort of vermiculite and cement around them as an insulation layer unless the ones @nod fitted are different. 

 

You have a choice with a built in liner - class 1 or class 2. Class 1 can be for anything including wood burners and solid fuel, oil and gas. Class 2 is oil and gas only. 

 

For the small difference in cost I would fit a class 1 liner and ensure it’s sealed correctly then fit a gas cowl to the pot. It means in the future it can be swapped for anything and is not limited to just gas. 

[nod]

3 hours ago, dpmiller said:

Are those concrete flue pipes rather than clay?

Yes 

[nod]

3 hours ago, PeterW said:

They look like Dunbrik liners. I’ve used them, should have some sort of vermiculite and cement around them as an insulation layer unless the ones @nod fitted are different. 

 

You have a choice with a built in liner - class 1 or class 2. Class 1 can be for anything including wood burners and solid fuel, oil and gas. Class 2 is oil and gas only. 

 

For the small difference in cost I would fit a class 1 liner and ensure it’s sealed correctly then fit a gas cowl to the pot. It means in the future it can be swapped for anything and is not limited to just gas. 

They are Dunbrik 

The flu guy said to use vermiculite or a very lean sharp s&c mix

He eeccomended the later 

Not picture But we have two sharp angles He seemed to think it would hold everything together 

[PeterW]

Are they not glued together too ..?? 

[Ed_MK]

thats AWESOME guys thanks,

Now I am getting an idea of how they need to be..
I was ridiculously naive by the looks of it ....

and I have a NEW Building Inspector coming today ....shame, I loved the one i had !

 

As usual (because i know you all love them LOL) ..I have attached a sketch !

and some photos too

 

Yesterday the wife asked me to slam on the brakes ...she had seen a reclamation yard ..

..well basically a company that grinds up demolition for hardcore ...but has a nice earner on the side flogging stuff too good to 

crush.

 

...and you guessed ...30 minutes later and £150 poorer we left with 2 great lumps of 2 inch slate ....17in square for the gatepost copings

(they are nice to be fair) ....oh and 2 chimney pots! roughly 30cm wide each (sigh) ...it seems 1 is never enough !

 

SO I was looking at your guys photos and stuff and did myself a little sketch ...I have the brickie coming and I wanted to make sure that 

me, him, the missus and the new BCO were on the same wavelength 

 

I hope you can see by my sketch how i "think" it goes together ....and you won't believe this ....but in the father in laws garage is about 10 circular
clay liners ....his missus was going to use them as planters ...but never did ...are they any good? will they save me a bob? ...I dont know
but they are there!

 

Anyway ...my questions to the wise

 

We only EVER plan to use a gas "pretend wood burner" thingy ...SO I dont want to over spec anything that would cost me more, but i want to keep the BCO
happy too and dont want to cut corners ...wit the above in mind ...

 

1. This 2 chimney idea of the wife's ...apart from having one working and one dead on the roof ....can i just block one up ..as its a dummy ?

2. I wouldn't need to run a liner up a fake chimney would i...so it could be filled all the way up?

 

If these are the case ...then please ignore the fact that my sketches have 2 liners/holes in them ..if i dont need them ..then they are OUT..

I mean these are over £20 each ....and its a 7m run ...mabye 5 to a metre?

 

3. does the rest of my ROUGH measurements make sense ?

 

4. them 2 voids on Nod's image ....do they get filled as you build up ?

 

5. The bottom of our house is brick skin on TF with a 50mm cavity ...but the upper store is going to be polymer render on cement board/batten etc.
How will this affect the chimney regarding regulations etc 

 

6. I see nod is using concrete block ....presumable these will be "faced off" ...my chimney is made of brick through and through (or at least i thought it was going to be)
there must be some regulation (there is for everything else) that specifies "thickness" ....Am i wrong here or does a single row of brick sound a bit "ropey" tied in well or not ??

Some people tell me ....oh its GAS only ...you will be fine, stop panicking ....it can be any thickness ...just sling a 6" metal flue pipe up it, might not even need masonry liners,

but then i am SCARED to ask the BCO in case he goes all "CYRIL SUPERSPEC" on my a$$ !!!

 

...and starts suggesting all manners of fire resistant this and special pumice backings imported from a volcano in the China Sea and terracotta tubes made from the finest flame retardent clay from the depths of the deepest mine in Stock on Trent ...some questions are better not asked ...as I am sure you will agree

 

 

 

 

[PeterW]

11 minutes ago, Ed_MK said:

n the father in laws garage is about 10 circular
clay liners ....his missus was going to use them as planters ...but never did ...are they any good?

 

No - clay isn’t suitable for gas unless it’s fullt sealed anyway. The sections have to lock into each other and you will also need the throat section anyway to close off the chimney at the base or your chimney has nothing to stand on. Go on the Dunbrik site and look at what you need. 

 

With 2 pots, one will be a dummy so make sure it’s got a weep route to let water out above the lead DPC. Both need bird cowls too so get a pair to match ... 

 

And it looks like you’ve “reclaimed” a pair of pretty new Hanson chimney pots ....!!

[Ed_MK]

3 hours ago, PeterW said:

 

 

And it looks like you’ve “reclaimed” a pair of pretty new Hanson chimney pots ....!!

 

£50 THE PAIR ....good deal ?

 

[PeterW]

9 minutes ago, Ed_MK said:

 

£50 THE PAIR ....good deal ?

 

 

Yeh you probably saved a couple of quid a pot... ?

[Ed_MK]

Result ...I will buy Stephen and his Labourer a 99 if the van stops LOL.

Anyways I just had a Building Control visit ....Nice Man ...Knows his stuff and 

he pointed out some bits i have to get sorted ....obvious stuff i should have seen myself (sigh).

 

..but i did ask him about the chimney , and started going on about liners and Danbrik and all that 

and he suggested i look into an "twin wall" flue ....So i did online 

 

seems very twinky ..could be the stuff of dreams ?

 

Problem is ...does this still need something to be shoved into ?

so am i back to liners at £25 a pop to get up to 7m or can this twinwall pipe "freefall"

as long as it is secured top and bottom ?

 

Dont you think its strange to be thinking about Fire and Heating as we sit around tapping on a computer

pouring in sweat and sat in just our underpants ?

no?

....just me then!

 

 

 

 

[PeterW]

9 minutes ago, Ed_MK said:

Problem is ...does this still need something to be shoved into ?

so am i back to liners at £25 a pop to get up to 7m or can this twinwall pipe "freefall"

as long as it is secured top and bottom ?

 

Twinwall has to be exposed to allow for inspection so you can't build it into that chimney.

 

Stainless liner can be suspended from the cap but it looks crap tbh...

[Russell griffiths]

Do you have to go up the chimney 

our fake gas wood burner goes through the wall, out the back of the chimney, not up it. 

Obviously you end up with a surface mounted flue on the chimney stack, so just depends if it’s in a noticeable area. 

 

Just a thought. 

[Ed_MK]

Well the wife wants a chimney ...
 

We WERE both long-term city rat-racers and she loves anything that says "countryside" or "cottage" or wher you can see a tree!
(where we used to live if there was 2 trees within 6 foot they called it a park !) The dog walkers used to wear waders so the animals
could cock a leg on THEM ....as there was nowhere else to go

 

anyways ..I have been in thee this morning ..tidying and measuring 

 

#I have some pics too.

 

 

Believe it or not that gaping hole in the side of the house is NOT a drive in lounge!

its the gap left for the usual MAHUSSIVE Potton Fireplace . I hope you can see from the pics below

the way it is currently and i have a sketch with sizes to help

 

The pic that came from the Home Exhibition is a different house...but the same style of chimney

and the picture of the internal fireplace is what we hope to get to ...although ours will be wider ...I know!

 

I suppose what I am puzzled with is how to START off ...

 

One of the issues I will encounter right off is that the Bricklayer will be here before the insulation and screed is laid 

...but does that matter ? Could we just MAKE a base out of engineering brick or something to screed height ? 

There will of course not be the Insulation or Screed...but I am still waiting for Potton to deliver the Floor Insulation Pack

 

Another is Insulation ...I mean the whole house is wrapped in all this Kingspan Foil Panels etc ....But of course the fireplace

back walls and base (see above) will NOT be ...Is it s stupid question to ask if there is ANY insulation back there or not or do I cavity fill the 

void ..or something ...but fill to what even ..as there is no framework at the back at all ....floor to ceiling ...

 

I suppose whatever i do with my "silver tube" I will need some sort of lintel or throat ...bricked out of sight above  the beam ? I am thinking I will have to 
fix a cowl or something to take the pipe up ?

 

And then I am back to the liners ? I mean do I need them as a path for the Silver Pipe to go up ...Danbrik or Clay (although i can't see there being much
point with a fire resistant ceramic of any description, as it won't get HOT enough) ...but I am possibly wrong

 

To be honest I have SO MUCH paperwork from Potton its unreal ....they really DO have details on everything ....I can't fault them for that, 
but when it comes to the chimney and fireplace (which lets face it ...they are KNOWN for houses with lovely fireplaces...check Google) ...there is SQUAT
in these folders on how to go about the construction and spec of the Fire and Chimney ...not even a basic guide ...(sigh)...what this means is the untrained
self-builder (that would be me) ...stands looking at a CAVE of a hole in the house, thinking ...What the Fudge do i Do

 

and everyone i speak to has a different opinion or method ...So Far I have about SIX.. LOL. The wife even rung Huntingdon ..where the Gas Stove is coming from,

....they "don't do the brick bit" , "don't know about the brick bit"  apparently its a "minefield of regulations" ...and to get it wrong is "lethal"

 

Yeah ....thanks for that, makes us feel a whole lot better !

 

 

 

 

 

 

 

[PeterW]

Fireplace will be built twin skins with insulation between. That needs to be min 150mm if you are wanting any reasonable thermal performance. 

 

Chimney can either be a liner hung from the cowl down an open block work hollow and terminated top and bottom (mega draughty and crap thermal performance) or built with standard flue components and sealed properly and then insulated all round with vermiculite. 

 

@Ed_MK Flues are one thing you can’t make up on the fly - read the regs carefully !! Faults here have the potential to kill. 

 

What have Potton drawn on the plans ..??

[Redoctober]

@Ed_MK I'm not sure this is going to be of any help just yet but we too are having an external chimney built which will house a WBS, so in a similar position to you.

The attached photos show the "hole" from the inside [left hand opening] and the external shot will show where the chimney will be built. 

Our builder is planning to start the external block work this coming week. The guy installing the WBS will also be taking care of the following -  

Supply & fit - 5kw w/b stove, 1 Fresh air kit, installation materials including liner, vermiculite,  Granite hearth, Wood  Beam mantle and HETAS Certificate.                                                               The Joiner will have to board up the "hole" as we will not be having the whole opening as a finished product if that makes sense.

Hopefully, once our work starts, some further photos will assist.

 

In a final attempt to offer something constructive - during our research stage we contacted Stoves on  line and they priced it all up for us and sent through some "plans" / diagrams of how it was to be fitted. Might be worth your while if time is on your side?

[Ed_MK]

Thanks Red!

that a lovely crisp roof on there too!

how are you facing the dorma's ? ....render?

[Ed_MK]

1 hour ago, PeterW said:

Fireplace will be built twin skins with insulation between. That needs to be min 150mm if you are wanting any reasonable thermal performance. 

 

Chimney can either be a liner hung from the cowl down an open block work hollow and terminated top and bottom (mega draughty and crap thermal performance) or built with standard flue components and sealed properly and then insulated all round with vermiculite. 

 

@Ed_MK Flues are one thing you can’t make up on the fly - read the regs carefully !! Faults here have the potential to kill. 

 

What have Potton drawn on the plans ..??

On Potton Plans?

 

Well nothing ....just a Void with a C shape where they "presume" the fireplace is going ...but no internal makeup

see attached from Architect Drawings...but cant see anything on the Key to indicate what the hatched areas are ...

so I too "presumed" it was laid out for a REAL fire ..so the inner layer would be suitable for that ...and the brick outer 

would be a skin ..like the rest of the house ...

 

looking at the cavity as it is represented ..it SEEMS to be exactly the same visually
as the cavity around the rest of the house ....which is 50mm

 

You (and others) have scared me enough ...I think I will spec and price up ...Plan B

If i go away from the chimney liner terracotta option (which seems costly)...I think Dunbrik look good ..I will send them an email
see if they are more helpful than the stove people 

 

 

 

 

Edited July 7, 2018 by Ed_MK

[Redoctober]

53 minutes ago, Ed_MK said:

Thanks Red!

that a lovely crisp roof on there too!

how are you facing the dorma's ? ....render?

 

Yes they will be finished in K-Rend. The thing that is still up for discussion is how to finish off the boards - over hangs etc. Sorry not really up to speed with the correct terminology as yet !!

[PeterW]

1 hour ago, Ed_MK said:

On Potton Plans?

 

Well nothing ....just a Void with a C shape where they "presume" the fireplace is going ...but no internal makeup

see attached from Architect Drawings...but cant see anything on the Key to indicate what the hatched areas are ...

so I too "presumed" it was laid out for a REAL fire ..so the inner layer would be suitable for that ...and the brick outer 

would be a skin ..like the rest of the house ...

 

looking at the cavity as it is represented ..it SEEMS to be exactly the same visually
as the cavity around the rest of the house ....which is 50mm

 

You (and others) have scared me enough ...I think I will spec and price up ...Plan B

If i go away from the chimney liner terracotta option (which seems costly)...I think Dunbrik look good ..I will send them an email
see if they are more helpful than the stove people 

 

 

 

 

 

Hatched areas mean block or brick. 

 

The two  stubs are to support the inside edge of the chimney stack above but I assume what he means by those is them standing on a lintel that spans the full width of the opening just outside the outer skin of the building. This will need to most likely be an RSJ as i can’t see a concrete lintel spanning 8 ft or more and taking the load. 

 

The demon joint in all of this is going to be getting the frame to chimney breast air tight - if this was me I would sacrifice the 100mm all round and build a block work cell that will enclose the fireplace. This can then support the steel, and then in turn you can then seal this inside and out to the frame opening. First with foam and then with air tight tape both inside and outside to create a “closed” box. 

 

This can then be clad outside (with a cavity) and then inside (tight to block) once the floors are in and the brick levels are known. 

 

The only issue with all of this is closing off the roof of the inglenook as these are usually inside the building so non structural and yours is going to be part in and part out. 

 

I had considered suggesting beam and block but that sounds overkill ..!!

[Ed_MK]

hmmm ...you are right though (again!)

 

I mean we have a lovely 16x16 inch beam for INSIDE the room ..just under 3m long !

and this should EASILY take the weight of the face course that will be above it INSIDE ...I mean it will be supporting

(technically) ..no more than 150-200 bricks running up to the inner ceiling ... ..which i guess to be about 500 Kilos ...tops ?

what do you think? ...its a bloody BIG beam ....3 man lift ! 

 

Now the chimney OUTSIDE is another kettle of sardines !

I mean the sides are brick and run all the way up ...so does the outer face ....

but the INNER wall ..technically that runs just OUTSIDE the normal external line

 

..what this means is that all the weight of that side of the chimney will be supported by 

...well bugger all

 

SO i guess i need to get an RSJ fitted across that gap of 2.7 metres, this RSJ will be of course
higher than the Internal Oak beam ...(so it cannot be seen) ..and If I am right I will have to overlap it
no less than 150mm on each side and have it on something substatial ...I am thinking dense concrete blockwork

7.2N Stregnth ...sound good. This will be the blockwork cell that Peter states above and will essentially form a full

inner SKIN too.

 

the pipe from the Stove (which sits well back anyway..as that is the style) will pass directly under and to the back of the beam; 

on its way upwards. If my calcs are correct the new RSJ will be virtually OVER the top of the Gas Stove...but of course out of sight

 

But what RSJ? ....Rather than s/e it ....I think as its not an internal or supporting wall (for a room anyway) I could just OVERKILL it

and fit an RSJ that was well over spec and be done with it ? What do you think ?

 

If I say that the beam will be 2700mm and it will have an overlap on each side of 150mm+ then the span will be 2400 at most

Not sure how to do the next bit ...as technically a chimney is a rectangle of bricks ....but if i presume that the RSJ is just holding 

its own side up ...

...looking at the calculation of bricks per m2 and the average weight of a brick ...it gives me about 1200 Kilos across that span.

 

So if i over-killed it ....what do you guys think ....1500 Kilos? 2000 Kilos ?

 

What beam would you recommend ...?

 

and i DID download the trial of Supabeam that another forum suggested ....but to be honest ...there are that many variables and 

acronyms on there ....you would need to be an SE to use it properly !.....so whats the point !

 

 

 

 

 

[PeterW]

I’ll run it through beamcalc later. Won’t need more than a 152 but will check. 

 

And  the inner chimney face has to be separated from the timber frame by a cavity for fire reasons. So that would be done in commons or blocks. 

 

 

[PeterW]

5 hours ago, Ed_MK said:

 

 

 

 

Sorry - I keep going back to this and I’m trying to engineer out the mammoth cold bridge where the outer skin is going to sit on the beam as there is nowhere for insulation to go. 

 

whats the minimum width fireplace you would accept ..?? That one above is 8.5 bricks wide or about 1900mm, would you settle for 7.5 bricks or a finished opening of 1680..?? Mantel in that picture is at around 1500mm high. You could easily make it 1650mm square which a pretty big  opening ..!!