# Forum Home Renovation Heating & Cooling  Wood heater flue replacement

## Cliff Rogers

We have just bought a new wood heater & the flue needs to be upgraded/replaced. 
Following are the pics I took along the way. 
Does anybody have a copy of AS/NZS 2918:2001 ? 
I used the one page instructions that came with the new flue kit & bits I managed to find on the internet. 
Pages 4 to 7 of this doco was handy even thought it was for a different wood heater. Fig. 6 & 7 suit my installation best. 
First 4 pics are of the old flue coming apart.
Pic 5 shows the framing after I lifted the sheet.

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## Cliff Rogers

pic 6 spreading the framing to suit the larger flue 
pic 7 using some of the old sheet screws to hold the framing in place 
pic 8 metal brackets cut & bent to shape 
pic 9 outer flue hung in place supported by a sheet of material tacked across the beams inside the house. Positions marked & metal bracket tacked in place. At this step, a torpedo level was used to get the flue verticle & holes were drilled through the metal brackets into the flue ready for rivets 
pic 10 outer flue removed & metal brackets nailed in place.

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## Cliff Rogers

pic 11 non-combustable packing nailed in place 
pic 12 new flashing put in place. (not supplied in the kit, I had it made to suit) Thanks to the tip from Journeyman Mick for this idea. 
pic 13 hole maked & cut out undersize 
pic 14 edges kerfed(?) ready for bending 
pic 15 closer pic of 14

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## Cliff Rogers

pic 16 bending up the flashing with the correct metal bending tool.  :Rolleyes:  (tile cutters  :Biggrin:  ) 
pic 17 ready for the outter flue 
pic 18 outer flue hung in place 
pic 19 close up from the top 
pic 20 lined up verticle for fixing. (rivets through holes made earlier)

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## Cliff Rogers

pic 21 flashing folded in to the outer flue & coated with neutral cure silicon  
pic 22 dektite put in place & streached down & marked & the pulled up to have silicon bead run aroun the mark so it will seal 
pic 23 dektite put in place & popriveted down with more silicon under the edge 
pic 24 stay brackets put in place making sure it is verticle 
pic 25 strap fixed to the outter flue

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## Cliff Rogers

pic 26 the finished flue kit with the cowl in place

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## silentC

I like the metal flashing idea. Is that a standard practice in canetoad land, or was that your invention? 
I installed a fire the weekend before last. Just used a dektite straight onto the roof sheet. It hasn't leaked as yet. 
One thing I noticed the first time I lit it. The cowl was sitting right down over the outer when we put it on but after the flue warmed up, it lifted by about 20mm and exposed the vent holes. Does yours do that?

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## Cliff Rogers

Journeyman Mick may wish to add some comments but he said the trick was to pretend that silicon hadn't been invented & have the flashing made with that in mind. 
The flashing I have neatly spans the corrigations in the custom orb & has a sligh crease down the middle to make the water run off to the sides instead of straight down the flashing. 
Turning the flashing up as in pic 16 is so that any water that does make its way under the silicon will not drip down inside the ceiling. 
Any questions, comments, corrections in spelling & nomenclature welcomed. IE: dektite, thanks SC

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## Cliff Rogers

> ...One thing I noticed the first time I lit it. The cowl was sitting right down over the outer when we put it on but after the flue warmed up, it lifted by about 20mm and exposed the vent holes. Does yours do that?

  We haven't used ours yet. 
I'd guess that the active flue expanded more than the outer flue & lifted the cowl up.

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## silentC

Well yes, that's what's causing it. Just seems like a poor design to me. I reckon the cowls should be made to allow the inner to expand and contract without raising the cowl. The inner ring of the cowl is a tight fit over the end of the flue though, because the fat end is up. We thought about screwing the cowl to the outer but that would probably be a bad idea if the inner doesn't give. 20mm is a lot.

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## Cliff Rogers

Ours is a Maxiheat Drop Box Default Flue Kit.
The instructions say "Trim the two layers of gal to allow the cowl to sit neatly onto the active flue lenght. The gal should be trimmed not at the top but at the bottom, where it joins the lenght underneath. Now secure the cowl onto the active lenght of flue"  :Confused:   
The queer bit is that the picture right below it shows screws through the skirt of the cowl into the outer flue & the tube in the centre of the cowl that goes down inside the active flue is marked as "100mm Telescopic Extension"  :Cool:   
That suggests to me that the cowl is held to the outer & the active can slide up & down the centre part of the cowl.  
I will get up on the roof & have a look at it right after I finish my coffee. 
Oops, urgent job just came in, have to do it later.

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## silentC

Don't forget your PPE  :Smilie:

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## Cliff Rogers

Sunglasses.   :Cool:

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## Barry_White

> Just used a dektite straight onto the roof sheet. It hasn't leaked as yet.

  Hi Darren 
I have had two flues with the Dektites just siliconed down to the corrugated roof for 23 years and they have never leaked.  
The flue for the slow combustion stove doesn't have a cowl on it and the flues are just galvanised pipe and it is just starting to corrode around the top. I wish I had used stainless steel now but back then there wasn't much stainless around for flues. It looks like I might have to replace it next year.

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## silentC

The stainless doesn't last forever either, but it's better than gal! It ain't cheap though. I had to get my BIL to make up a replacement length for me and it was $46 in the book. Lucky for me he married my sister  :Smilie:  
The dektites seem to work pretty well. They should at least last for the life of the flue. We got this flue with the fire - both second hand. One of the s/s inner lengths had burnt through a seam but the dektite that was still attached to the outer was in good nick. We thought about reusing it but it was a bit small and we had a nice new one, so it's gone to the tip before it's time. 
Hope Cliff hasn't fallen off the roof. I'd feel a bit guilty about it...

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## ptc

You guy's would make a fortune in tassy.
Cliff super job.

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## MurrayD99

The council made me isolate the outer flue from the (square) support structure up at ceiling height. This was not required in the installation instructions but, OK, OK, sure, no problem, tear it out and re-do it with a bit of a gap and some 3/4 channel.  Suspecting such a development, I had not fixed the frame to the rafters properly.   You did a nice job Cliff.  Many happy warm nights.  BTW, it gets cold in QLD????  Really?  I thought it was a tropical paradise.

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## Cliff Rogers

Back now, panic over. 
The piece of tube in the cowl is a sliding fit inside the SS active flue pipe. 
I have about 100mm for movement & currently the active flue fits about 40mm over the cowl piece so it can expand at least 60mm before it starts to push the cowl off. 
Yeah Muzz, we are 865M above sea level, just below the clouds most of the time & just in the clouds some of the time. 
Coldest during winter is 5° normaly around 11 or 12°

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## Cliff Rogers

> ....The dektites seem to work pretty well. ...

  I recycled the one I had on the old flue 'cos it was only a couple of months old.
The old one leaked heaps, I must have poured 2 tubes of silicon onto it trying to stop it & when I ripped it off to put the new one on I found that the previous job had been done by a dill who didn't clean the roof properley before he glued it down with some tacky grey goop.
There was mould under it so it wouldn't seal properley. 
The new one done right was working fine but when I mentioned it to Mick, he came up with the flashing idea. 
Those 2 lengths cost me $72 & I reckon it is good insurance.   

> ....Hope Cliff hasn't fallen off the roof. I'd feel a bit guilty about it...

  Sorry, I had to dash off & just edited the post that said I'd get back to you after I finished my coffee.  :Redface:

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## Cliff Rogers

> The council made me isolate the outer flue from the (square) support structure up at ceiling height. This was not required in the installation instructions but, .....

  It is covered in AS/NZS 2918:2001 (that you have to pay for  :Rolleyes:  ) 
See the link to the pdf in my first post....page 4, para 5 & page 7, fig.8 
There should be 25mm of non-combustable packing between your outer flue & any combustable material if you intend to use it as a support.

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## joe greiner

I totally, completely, thoroughly agree that flashing is the first line of defense/defence. One of the first things they teach in civil engineering school is that water goes downhill. Any encouragement you can give it is time and money well spent. 
Joe

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## journeyman Mick

While it's entirely possible to just use a dektite and not get leaks I've fixed enough leaky roofs not to place my trust in them or sealant alone. It's the only waY I'll do roof penetrations. 
Mick

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## MurrayD99

> It is covered in AS/NZS 2918:2001 (that you have to pay for  ) 
> See the link to the pdf in my first post....page 4, para 5 & page 7, fig.8 
> There should be 25mm of non-combustable packing between your outer flue & any combustable material if you intend to use it as a support.

  
My BIL installed a pot belly stove in his upstairs lounge and "dogged" the heavy steam pipe he used for a flue onto the rafters.  Sort of zero clearance approach, very strong!  That stove could be made to go translucent when stoked with coke.  Also the steam pipe got a nice red.  Very warm indeed.  Even warmer the day the rafter caught fire and the fire brigade appeared....  But that was an extreme case I think.   :2thumbsup:

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## Cliff Rogers

It is because of pyro's like him that we now have the standards.  :Rolleyes:   :Biggrin:   
We used to just have a 4.5" SS active & a 9" Gal outer that was screwed straight to the wooden boxing in the ceiling.
We could get our old Masport Fatso to glow in the dark too & it didn't even discolour the timber in the ceiling.  :Tongue:   
Now we have a 6" SS active, a 9" Gal inner & a 10" Gal outer & it has to have another inch of seperation from anything combustable.  :Cool:   
It rained today & it hasn't leaked. (yet)  :2thumbsup:

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## Barry Hicks

G'day Cliff.
Where you when I lived near Millaa?  I had to get a plumber to do mine as I couldn't afford a divorce. 
Barry Hicks

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## Cliff Rogers

When did you live up here? 
We are at Minbun, have had the place for a bit over 4 years now.

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## Cliff Rogers

And up she goes.    :Biggrin thumb: 
Only 18° outside, don't need it realy  :Rolleyes:   but I wasn't going to wait since I just finished it.  :Biggrin:  
I does help to dry things out a bit 'cos we are in a cloud at present.

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## ozwinner

Theres nothing quite like a fire is there?  :Cool: 
Just as long as its supposed to be there.... :Doh:  :Shock:  
We lit ours last weekend and it will stay lit until 2025.... :Biggrin:  
Al  :Smilie:

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## jack620

I know this is an old thread but I thought some of you might be able to answer a few Q's for me. 
The guy who installed my wood heater flue (in VIC it has to be done by a licenced person) was some kind of silicone junkie.  the stuff is everywhere and I'm sick of looking at his dodgy work every time I go on to my deck for a beer.    
I'm going to remove the ugly angle bracing he used on the roof (not required as the flue only penetrates out about 1m), fit internal support brackets to the ceiling joists (as per the flue manufacturer's instructions) and replace the dektite flashing. 
When the guy installed the flue he screwed the outer casing to the roof sheeting.  I recall reading somewhere that you shouldn't do this but I can't recall where.   Does anybody know if this is prohibited in the applicable AS?   If so, I will need to remove his screws before I fit the new dektite.

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## Cliff Rogers

> .....When the guy installed the flue he screwed the outer casing to the roof sheeting. I recall reading somewhere that you shouldn't do this but I can't recall where. Does anybody know if this is prohibited in the applicable AS? If so, I will need to remove his screws before I fit the new dektite.

  I wouldn't join them together as the expansion & contraction of the roof sheeting would push & pull the casing around. 
I don't know for sure as I don't have a full copy of the standard but if you look at my pics & the last 4 pages of this doco, the roof sheeting does not contact the outer casing at all. 
The outer casing is fixed to folded metal brackets that are fixed to the roof frame underneath the roof sheeting.
In the old days, the outer casing was screwed/nailed/fixed directly to noggins in the roof cavity.
Now, under the standard, there has to be a 25mm (1in) minimum separation between the outer casing & any combustible material.

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## bricks

> Now, under the standard, there has to be a 25mm (1in) minimum separation between the outer casing & any combustible material.

  
Two questions clif- is your flue single skin or double skin?
Is it bigger than 150mm and single skin? 
If it is then the required clearance is now 75mm  
Nice work tho bloke, I do roofing a fair bit and I'm not too proud to admit it aint my strong point. Usually the faster I work, the longer it takes me.
well done. :2thumbsup:

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## Cliff Rogers

> Two questions clif- is your flue single skin or double skin?

  Double, it has an outer & an inner casing & the active goes inside that. 
The old one had been there nearly 20 years & it was a single skin, 230mm casing with a 115mm active & the casing was screwed directly to the hardwood frames in the roof & they had barely even changed colour & we have had the active glowing in the dark.  :Biggrin:    

> Nice work tho bloke, I do roofing a fair bit and I'm not too proud to admit it aint my strong point. Usually the faster I work, the longer it takes me.
> well done.

  Ta, Journeyman Mick gave me the tip on the turned up flashing.
He said to try to do your roof penetration as though silicon sealant didn't exist & then it wouldn't leak, thanks Mick.  :2thumbsup:  
I did the same trick for my exhaust ducting roof penetration.

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## bricks

looks like you have it all under control,

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## wonderplumb

Roofing isnt my strong point either, I like doing gutters and downpipes etc but anything too involved in the roofing dept. goes to the professionals. :2thumbsup:

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## bricks

I'd prefer someone else did it most of the time too.

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## jack620

> I wouldn't join them together as the expansion & contraction of the roof sheeting would push & pull the casing around.

  That's what I figured.  I notice the document you linked to says the Standard requires the flue to finish 4.6m above the hearth.   Mine is nowhere near that tall.   Seems the bloke who installed mine didn't know his a#*@ from his elbow.  He also used bugle-head screws to join all the pieces together which will make sweeping the flue interesting. 
Looks like I've got some work to do.

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