# Forum Home Renovation Heating & Cooling  Installing wood burner in existing fireplace

## koots

Hi guys, first post here. 
We have an old open fireplace in our 100ish year old home, however smoke leaks into the roof space as some of the mortar has fallen away in the brickwork. It's just single skin brick. So we are going to install a slow combustion heater and run the flue straight up. 
Couple of quick questions.  
1) We were told by the people selling them that all we needed was the single active flue. I quizzed them on whether or not the gaps in the mortar changed anything which they assured me didn't - there is a piece of hard wood wood framing supporting the plaster about 1200mm above the top of the stove, other than that there's no combustibles on the other side of the brick. (That being said, the plaster is the old horse hair (??) type, I've always assumed it's not combustible until now...?)  Will there be enough heat radiating off the active flue that we risk a fire with the gaps in the mortar? There will be an air gap of about 25mm between the pipe and the brickwork. The old bricks are 110mm wide so where there is any mortar holes there will be a 135mm air gap between the flue and the wood - if there is any holes where the wood is. The chimney is too narrow to get inside so I can't be sure exactly where the holes that penetrate entirely are. 
2) We have push together SS flue pipes, is it ok to push them together not entirely square? They will be secured with stainless rivets. Whilst it sounds dodgy a few of them are extremely tight fitting, to the point where I will need to use a mallet to seat them completely. I only need to get a 10mm offset over a metre because of a couple of narrower courses or brick, so it's not very much. I'd almost assume that in these sort of installs, with no support other than at the top of the chimney this would almost happen naturally over a 5m run anyway? Especially after a bit of expansion and contraction? 
Cheers!
Koots

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## NRB

HI koots,did one years ago so will watch with interest what is ok today,one thing I was told is that the pipes join with the upper one going inside the lower one,this was expained to me  to allow any gunk to stay inside and not leak down the outside of the flue, as I said will watch replies.

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## SilentButDeadly

1.  The sales mob were right.  Make sure you fit a flue ceiling collar to the plaster panel - that'll prevent scorching etc. 
2. They can go together out of square & true (smoke isn't square so a flue doesn't need to be either!).  As NRB said....upper goes into lower rather than the more obvious upper over lower.

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## koots

Thanks guys, 
However, the flue doesn't penetrate any plaster, it extends entirely through a 100 year old brick chimney. My concern is the heat from the flue penetrating the mortar gaps and igniting any combustibles on the other side of the brick? There is 1 length of hardwood fixed horizontally to the brick with a very slight air gap, about 1200mm higher than the top of the wood stove. And does anyone know if the old plaster with hair in it is combustible due to the hair!? 
Cheers!

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## Moondog55

You will need a collar of some sort where the flue exits the old chimney and you will need a wind cap on the flue. You should be OK about heat loss through the gaps where mortar has gone but you should check after it gets a workout and heated up to be on the safe side
How close are the combustibles to the old chimney? if more than 25mm or so I wouldn't worry too much
As far as I know the old horsehair plaster isn't at all combustible

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## koots

Yep, I'm going to support it where it exits the brick work, and the existing clay chimney pot will sit over the top of it with a bit of clearance for expansion. 
The only combustible (the piece of harwood) would be about 5-10mm maximum off the brickwork, depending on how straight the brickwork is. It exits right on the join between the bottom of a gable and start of a skillion so viewing is extremely limited. I have to lie and crawl to the edge of the roofspace and hold my phone over the top of the wall and use photos to check it. Attached is a photo showing the clearance, bottom centre. The void is due to the width of the chimney breast from floor to ceiling, though the chimney itself is a single lined structure inside it - and before anyone says anything, I do plan to try and vacuum those leaves out haha. We use an industrial vacuum service at work so hoping to get their hose in by pulling a roof tile out. 
Nice to see others agree with the shop, I wasn't too worried until the installation manual had minimum clearances of like 500mm from any combustible walls to the flue and I thought christ, I've not got anywhere near that where mortar has fallen out. Stainless doesn't transfer heat as well as mild steel or other metals so hopefully after the first section of flue it won't be all that hot anyway. 
Cheers

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## koots



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## Moondog55

My experience tells me that the only top that will work with a SS flue is a dedicated circular [ annulus] style and insulating the section of the flue that is above the chimney is almost essential to get a good draw up the flue http://wildcatindustries.com.au/wp-c...nching-017.jpg

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## koots

Why is that mate? Is the chimney pot too restrictive? The one I have already is similar style to this : http://img.archiexpo.com/images_ae/p...93-6232609.jpg though with 4 holes at the top not 2. 
I wasn't going to have any of it above the chimney, the brickwork already extends over a metre above the tiles. Or did you mean insulate that section as the brickwork is exposed to wind etc? 
Cheers

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## Moondog55

> Why is that mate? Is the chimney pot too restrictive? The one I have already is similar style to this : http://img.archiexpo.com/images_ae/p...93-6232609.jpg though with 4 holes at the top not 2. 
> I wasn't going to have any of it above the chimney, the brickwork already extends over a metre above the tiles. Or did you mean insulate that section as the brickwork is exposed to wind etc? 
> Cheers

  No I mean that you need to extend the flue above the chimney height to allow fitting of the windcap and insulating that small section to stop cooling of the hot flue gases [ smoke] otherwise when the wind blows the smoke cools and becomes denser and you get a blow back into the house. The annular style is simply been shown to be the most efficient as it handled wind from any direction plus vertical down-draughts
About 300mm is enough tho but the exterior shielding may need to be cut down to size. 
What sized flue has been recommended to you? Bigger is often better and 150mm diameter is the usual minimum these days

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## Marc

If you want your flue to work properly you need double skin. The inside 6" the outside 8" as a minimum. You don't say what size slow combustion you are buying. A single skin flue in a closed cavity without ventilation next to wood is clearly a no no, and as mentioned by others, single skin cools down and you get your flue clogged by tar very quickly and it will not draw properly. The brick chimney does not provide the same insulation a second flue provides and keeps the smoke hot and flowing fast

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## koots

Ah right o. Yep its a 6 inch flue. The heater  is a Nectre 15 LE and is designed for 6 inch.

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## koots

Thanks Marc, as for not ventilated,  I had decided against installing a register plate at the bottom. The shop (who also do these  installs reguarly but didn't  want to because they're  very busy currently) recommended closing up the bottom to stop heat going up the chimney as well as the top obviously sealed. I figured that  closing  both would  as you say leave it un-ventilated so was going  to leave  the bottom open to begin with. 
What do you think? The gaps in mortar aren't  huge but they were enough to leak a small amount of smoke upon initial lighting of the open fireplace.

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## Moondog55

Install the register plate or you lose too much heat up the chimney. Using a second skin inside a chimney isn't usual here but I have heard of it being done, definitely needed exterior to the chimney
An alternative idea [ merely an idea] may be to fill the chimney space with non combustible high temperature resistant  insulation like rockwool

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## koots

If installing the register  plate then should I provide some sort of ventilation at the top?  Otherwise  any heat has nowhere to go but through  the cracks  in the mortar?

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## SilentButDeadly

> If installing the register  plate then should I provide some sort of ventilation at the top?  Otherwise  any heat has nowhere to go but through  the cracks  in the mortar?

  It's not that much heat transmitted to begin with (because air is a good insulator) and what little there is will be absorbed by the bricks.  Fit the bottom register plate.  If there's room and you are still concerned then you could go with a second skin and then the cowling at the top will cover both and allow the air space between the skins to breathe. 
Nice choice with the Nectre by the way.  Very very good fireplace...

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## koots

That was what I was hoping to hear, air being the best insulator. I'll leave it off to begin with so I can shoot a temp gun up the chimney to settle my nerves initially haha. Thanks fellas. If there's any dramas I'll update the thread. 
Cheers

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## Marc

With this DIY install you have to beware of insurance. In the remote case of a chimney fire and a claim, if it is not done according to regulation it may backfire (pun intended). 
My experience in installing slow combustion is limited to 3 installations done in two different houses. Two with all metal flue and one in an existing brick chimney.
One of the heaters has double skin since it is single storey. Second heater goes through mezzanine so has 3 skin, 6-8-10 from the ceiling all the way to the hat. 
Third one I installed in an existing fireplace. It was a disaster and never worked properly. I could only fit a 4" flue inside the very small chimney no chance for a second one. The heater was small but the flue never worked as it should. In hindsight I should have gone to a sheet metal place and get a rectangular flue custom made to fit in the brickwork and a second one inside. 
In your case it seems you have enough room for a 8". Bottom plate to close the gap off, is needed, at the top you can have a short piece of 10" and seal around it, and cover with the right size top that allows for ventilation of all 3. Remember you must go I believe it is one meter? Better check that with council, over the ridge of the roof.

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## koots

Yea the insurance part is why I'm asking the questions. The shop, having done these installs for 20 years apparently and 'always passed any inspection' were adamant single skin is fine and just bring it to whatever height the existing chimney is, as it is an existing chimney. That part I doubted as it may be an existing chimney but it's a new flue install. They didn't even mention the 300mm forward required on the hearth. I found that out afterwards and have now had to re-tile the floor aswell... haha. Anyway here is the code for anyone interested: 
a)  the minimum height of a  flue system within 3m from the highest point of the roof shall be 600mm above that point  
b)  the minimum height of a  flue system further than 3m from the highest point of the roof shall be 1000mm above roof penetrations 
Even though I'm pretty handy with most jobs (make a living as a fitter), I had wanted to have it professionally installed for the purpose of insurance. I mean let's face it, the whole point of the install is so I can light a fire in my loungeroom. Seems silly when you say it like that I reckon haha. When I asked about install though, they not only wanted the cost of the contractor to install it, but also wanted to charge more for the stove. Apparently they'd given me the 'cash and carry' price - which I might add I bargained down a bit because it was $250 more than anywhere else anyway! 
Anyway, the actual job is a breeze for me, just wanted opinions on the mortar gap issue and whether it was 'acceptable' to join the flue pipes at slight angles. My experience says of course it's not an issue, due to them not being sealed anyway and being at negative pressure due to draft, but once again was worried about code etc.  
Cheers guys

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## koots

Hey guys, 
Fireplace is installed and working beautifully. Plenty of draft, and none of the brickwork gaps is leaking too much heat. Ended up having to pull plaster off around it to clear the leaves in the above photo, (just gotta work out how they got there now! all were fresh to can't have been there long or it would be a compost pile. filled two shopping bags full!) so was able to check the brickwork in a few different places. 
Definitely losing heeeaps of heat without the register plate, so was going to make it today and just thought I'd run an idea past you guys. Has anyone not bothered with a plate, and just packed it full of non combustible insulation? Was thinking that then I can remove the insulation easily in summer as the natural draft on the chimney helps with keeping the house cool. If the steel plate is definitely needed then I'll make it in two pieces so it can be removed easily. 
Anyone done something similar? 
Cheers

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## Moondog55

Lots of ways you can improve the efficiency and recover that heat in the chimney space if you don't mind a hole in the plaster. 
Can we see a picture showing the installation?

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## koots

Here you go mate. I know someone is going to mention the tiles - they're not finished yet as I wanted to install the stove and then measure my 300 forward as I want to have the minimum number of rows. 
I'm assuming you're going to suggest a fan in the brickwork that pulls the air back into the room through a vent in the plaster? What are your thoughts on my idea of just jamming the bottom with insulation and not having the steel plate? I know bugger all about insulation, only been a homeowner for a year now but it would make sense to me that perhaps the steel is required. 
Cheers

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## Moondog55

If you don't mind removing a few bricks from the chimney [ with a suitable lintel and grill or holey bricks] you can put a decorative grill up near the ceiling and allow natural convection to recover that heat from the chimney and heat the room. You put the collar over the flue just slightly below the ceiling height and fill the rest of the cavity above that with rockwool
Very pretty room BTW. So the flue heats the space in the chimney then as convection takes the hot air up and into the room cool room air flows into the bottom of the chimney space

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## koots

Brilliant idea. Wish I'd thought of it myself when I could still access it all from the top, before I redid the concrete chimney cap haha. I'll have to remove enough bricks to get my arm up inside and pack the rockwool in hard as I won't be able to get a plate in up there now.  
For curiosities sake, was my idea about swapping a steel register for rockwool at the bottom any good? I still like the idea of being able to open it up in summer to draw heat out of the room.  
These god damn DIY projects never end do they, just keep on evolving haha.

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## Moondog55

Smashing the new concrete cap will  be easier and in the end possibly cheaper
To draw heat out of the room in summer just prop the door open
I've only done this chimney mod once but it was brilliant, can't do it here now as I demolished the chimney to get a big window in

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## koots

Yea sounds really effective. Was it noticeably different when you did it or did you just find you were using less wood to heat the place? The jetmaster inserts work on convection and are supposedly pretty good too. Just when I thought I was nearly finished too...  haha 
Thanks mate appreciate the input.

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## Moondog55

Seemed to be warmer all around, probably because the convective currents broke up the stratification effect where the warmer air sets up high and it gets progressively cooler as you get closer to the floor

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## Marc

Sorry guys but I doubt that is a good idea at all. 
A brick chimney is hardly a good barrier for foreign matter to accumulate against the metal flue that can reach temperatures of 800 degree if you get carried away with the fire, and in normal circumstances easy 200. You have already found that out with the amount of leaves you found. Add to that rodents building a nest with straw and feathers and rags and paper and you get the picture.
That is why you need a second flue to shield the combustible material that can accumulate around it and to make it draw better and avoid creosote condensing against the sides, further up the flue. The second flue must also be on a perforated plate so that any rubbish accumulating can either fall through or be seen and cleared. 
To stuff insulation around it is just a disaster awaiting to happen. The rockwoll will not burn but add to it creosote and rubbish and you get a fire chimney quick smart. Furthermore... if I remember correctly you had wood work visible inside that cavity? Close to the naked flue at 800 degree? 
To recirculate heat from the flue is possible but should only be done within a metal jacket that covers the brick, and goes through the bottom plate leaving an opening to draw air from the room and blocked off at the top with a side opening to get back in the room at celling height.  
Simple device but must be done with all the precautions of a conduit that carries FIRE not only smoke right against the wooden structure of your house. 
Google chimney fires and you will find a lot of info.
My 2 cents worth

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## Moondog55

Woodwork is outside the brick chimney.
Marc a second flue would imply a double flue when I think you really mean a heat-shield
in this instance the original brick chimney is acting as the heat-shield
 Rockwool goes between the  flue and the brick of the chimney and it's purpose is to keep what remains of the heat in the smoke hot enough so it doesn't condense . No fuel inside the cavity between the flue and the brick so a chimney fire isn't possible. The passive convection around the steel flue is enough to stop the temperatures inside the brick chimney getting too hot anyway. You can extract a lot of heat as there only needs to be 200C difference in the top to bottom temperatures of the smoke for a good draw
I've done one of these but have seen a lot of them in and around Mt Beauty / Bright and in no instance did the old brick chimney need secondary lining

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## Marc

So you are saying that a flue that can get red hot can be safely packed with insulation around it and allow combustible debris to accumulate against it without any risk of fire ...  

> No fuel inside the cavity between the flue and the brick so a chimney fire isn't possible

  I beg to differ. 
I am afraid that the fire brigade will have something to say about that.
I had my say. 
I am not interested in winning a debate, just stating facts.

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## Moondog55

No Marc; I am saying that you are making assumptions about things you have not examined properly.
I'm wondering how you think all that combustible material is going to get inside the sealed chimney in the first place?
I've done the course and I see no risk

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## Moondog55

Yes I see how you are thinking but that picture is not the chimney, it's the space surrounding the chimney. Actual chimney looks to be on the left of that picture and if it is the same as one I just demolished the gap between timber and brick is about an inch in old money
Before the flue was inserted into the chimney there would have been the possibility that a fire could have started there and the OP should seal off the gap under the eaves to keep the cavity clean for the future but the chimney itself is both an excellent heat shield and non-combustible buffer. Even if the flue has a temperature of 1200C at the bottom where the smoke exits the firebox the brick exterior will take a long, long time to heat to the point where it radiates sufficient heat to set fire to the timber on the outside, in it's own right it is a non combustible shield
By ventilating the chimney cavity and extracting the flue heat to warm the room the brick should never get hot enough to be a risk, my experience is that the convection can actually rob so much heat from the flue that getting the fire to draw initially can become a problem so a the vent near the ceiling needs to be closable so the flue can heat up when starting the fire.
I would not be encouraging koots to do anything that was a fire risk

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## Marc

Yes, I understand that the frame as seen in that picture is safe, however if you have done the course you probably know that chimney fires in proper full brick chimney that are covered with creosote can catch fire and the fire can travel through the loose mortar, between the bricks and get to  the roof. That is why when a slow combustion is retrofitted the council requires a second flue as heat shield to safeguard from this hazard. Insulation packed between brick and flue would make things worst. the brickwork that is 100 years old will hardly provide a safe firewall, but hey, like I said, not here to win any arguments, just making my view heard that is all. 
 mm I wonder where did that picture go?

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## Moondog55

Council in NSW must be taking a totally different view to Victoria. 
When I last checked [ just before demolishing the chimney ] only the primary flue was required.  
I hope this hasn't left koots totally confused
PM incoming

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## koots

It seems to me there is a post missing about now from you Marc? Or perhaps Moondog just posted twice in a row. 
What I am confused by Marc (not getting up you either, just trying to learn), is what combustible material is going to be inside the chimney? There is no creosote build up inside from past open fires. Some staining yes, as would be expected, but no buildup. The leaves were like moondog says, in the cavity between plaster and brick - external from the chimney. It can be seen in the pulled back photo showing the holes I cut to clean it out. I've left those holes open for now so I can check the brickwork and it is stone cold even after 3-4 hours or running the fire. I will add that the wood framing isn't an inch off but barely 10mm in some spots. I would've expected it to have been at least an inch personally. I've had the top of the wood stove at well over 300+ measuring with a temp gun (it maxes out at 300andsomething), and can hold my hand on the brick surrounding it inside the fireplace. Hot, but can still hold my hand on it for a while. At the moment the chimney cavity is ventilated at the top so heat is rushing out of the old brick chimney. Hence the most recent question regarding register plates etc. 
As for it being law, if that is true I'll have to look into it, as when I was looking at different fires, two different fireplace shops both said I only needed the single skin active flue if installing it inside an existing brick chimney. One of them is part of a larger construction company too.
That being said, it still could be a regulation. I had actually looked and couldn't find anything regarding installing into brick chimneys but also couldn't get an entire copy of the standards. Do you work in the industry? Or know someone who does that can actually confirm it for me?? 
Cheers guys

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## Marc

I personally know of one home fire that was traced back to a chimney fire in an unlined brick chimney. Fire made it through the gaps in the bricks aided by buildup of creosote and tar.  
A single skin flue efficiency compared to a double skin flue is day and night. Many obvious reasons for this. The brick of the chimney does not act as a second metal flue would.
With time, there will be build up of matter between the flue and brickwork. You need to be able to remove the bottom plate and clean this out. A second liner with a proper perforated bottom plate that allows a small amount of air to circulate between the first and second flue, will keep this gap free and effective as a heat shield. The top of the flue has a ring to cover the second lining and vent it. 
Of course all this is academic if you don't have the room in the chimney for a second lining. 
Legalities aside, that is not my area of expertise, I have seen single skin flue go through plaster ceilings without anything else and through metal roof and past rafters and the house did not burn down. Probably because the owners were stingy and burned green rubbish and the flue probably never got hot. 
So your install may or may not be dangerous, as long as you don't stuff insulation around it.

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## Moondog55

Well you do need to seal the top of the chimney where  the flue exits , that should be a priority, otherwise you are losing all your heat to the outside [ also stuff can and will fall in there] as to the register plate you should do something to make the heater more efficient. 
I prefer my way but given Marcs comments I am going to do some double checking on the situation here in Victoria.

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## koots

Thanks fellas. I'll  have to give it a bit more thought myself as there isn't  room for a second skin anyway like you mention Marc. 
What's  your opinion Marc on the usual steel register plate  at the bottom having a layer of insulation on it? Obviously fire resistant insulation. I was going to make the plate  removable anyway because I just don't  like the idea of not being able to get in there for an inspection once in a while.

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## Marc

I personally don't want anything in the way of inspection and cleaning. The plates used for ceilings have a second ring with a second shield to protect the celling and avoid direct heat from hitting the plaster.  In your situation there is nothing to protect. What do you want to achieve with insulation? Heat escaping thought the plate up the chimney cavity? If you have the top capped, there isn't much circulation happening. Recovering the heat from the flue that is trapped between flue and brickwork would be nice. You can always line the brickwork with a custom made rectangular liner, but anyway, I have interfered with your project far enough ...  :Smilie:

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## koots

Thanks for the advice bud.
Cheers

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## koots

Sorry blokes one more thing. Once I decide what  road to take. Can anyone see a problem using bgc fibre cement to make the register plate or top seal? Non combustible but will it smoulder at these sort of temperatures? 
Cheers

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## Moondog55

Use steel, as you can buy the top plates ready made with the hole in and trim them to size.

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## Moondog55

Heating and cooling | YourHome  http://www.vba.vic.gov.au/__data/ass...el-Heaters.pdf 
According to the Victorian government we are considered to be too stupid to follow directions and common sense so it's a restricted trade here apparently, not that this has bothered anybody I know in the country areas

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## David.Elliott

Moondog, 
There are indeed some stupid folk out there...it's all well and good to have directions, but some folk don't think to refer to them.. 
The neighbours are in the local volly fire brigade. In that capacity last year they had some fun in attending a fire in a two storey home near us.
Recent new owners
Previous owner had installed wood fire
SINGLE flue straight through the chipboard flooring with they think 15mm clearance all around
Then the carpet was taken all the way up to and neatly tucked in around and touching the flue. 
Surprise, surprise stuff caught fire. 
Worst of all was the floor framing was all TP, and for many many days continued to smoulder inside the timber releasing God only knows what 
Same day, same development, fire on stove, caught the PVC ducting which then melted and fed the fire which the grew out into the wall cavity and ......on from there

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## Moondog55

Candidates for the Darwin Awards should not breed.

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## plum

> No Marc; I am saying that you are making assumptions about things you have not examined properly.
> I'm wondering how you think all that combustible material is going to get inside the sealed chimney in the first place?
> I've done the course and I see no risk

  I read this with interest yesterday, and wondered, 'what course'?  I am registered to install 'SFH', but not licensed, and am not interested in becoming licensed in them. Is there a backdoor way of becoming licensed?

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## Moondog55

CFA Fire risk assessment course. Not any sort of "license" just training in looking for and seeing how things could go wrong

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## SilentButDeadly

> Candidates for the Darwin Awards should not breed.

  Then we'd have nothing to watch on Youtube... :Cry:

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