# Forum Home Renovation Heating & Cooling  Mini orb on wall behind wood heater

## Kirsty B

I am new to renovating but both myself and my partner are obsessed by the idea of framing mini orb on the walls behind the wood heater that will sit on a slate hearth in a corner of the lounge room.   I haven't been able to find much info about it on the internet other than it is advised to leave room between the mini orb and the wall for air flow.  Is there anyone who could give me any more information?

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## Moondog55

Seen this done many times, first response is always to ask you local council to see if they have any specific requirements but in one friends house she had to use cement sheet behind and against the wall with vertical  steel *"U"* or *"Z"* brackets, the mini-orb screwed to the brackets and a 25mm air-gap between the cement sheet and the mini orb and all the way, floor to the ceiling. from memory the gap at floor and ceiling was also 25mm to allow the air to move ( it was single skin flue and it was a while ago- these days I think a double skin flue is the minimum) and the gap had a layer gal steel angle against the sheet on the wall. 
I have seen similar installations where two layers of steel were required by council, each with a 25mm air-gap, the first steel sheet usually flat plate and often decorative pierced plate used as the second, visible shield.
I love the look of these myself and I'm trying to convince the Minister of War and Finance to plan a wood fire for our extension.

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## SilentButDeadly

Moondog has it fine.  Basically you fit Rondo furring channel to the wall behind the fireplace and attach the miniorb to that with wafer head screws.  Top or frame out out the wall with a metal flashing to suit and you are done.

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## cherub65

Just looking at the BCA, and it states where a heat shield is used it must not be less than 90mm masonry. It should rise 600mm min above the top of the unit and have a 25mm gap between the existing wall and the masonry wall and a 50mm gap between heat shield and unit 
So would put up a masonry wall first then fix sheets to that

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## Moondog55

Not sure that's right Cherub, there must be deemed to satisfy provisions for alternative construction hidden in there somewhere, otherwise we could not use compressed sheet underneath the buggers.
There would be absolutely no point in using both masonry and metal.
I know I would be happy with double layer steel heat-shields myself with even the most basic of pot bellys but i would also not want to quibble with an insurance company trying to weasel out of a claim

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## Moondog55

http://www.sustainability.vic.gov.au...od_heating.pdf  *Heat shields*
The distance required between a wood heater and a plaster or wooden wall can be safely reduced by the use of correctly installed heat shields. Heat shields may be constructed from brick, metal, high-temperature fibreboard or a proprietary heat shield material. In all cases a ventilated or air gap must be left between the heat shield and the wall. 
that is the Victorian view at the moment as far as I can tell

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## cherub65

Would check through AS 2918 for confirmation on substitutes. Will try to dig it up later

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## Gaza

Fc sheet is normal not sufficient to provide fire rating, you will need a wall system of fire rated plasterboard ie 2 layers 13mm = 2hr or a fire rated board light promat makes.

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## Moondog55

I just noticed that SilentButDeadly has hit his second millennium with 2000 posts. Break out the bubbly and party

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## Moondog55

But we are not talking about a fire rated wall.
Anyway fire rated plaster is only rated for ceiling use, had that particular issue in another life. Although i think there are some new products that are designed for walls, need to double check.
Heat shields are used to lower the allowable distance between a hazard (wood stove) and a combustible wall. 
I have seen literally dozens of wood stoves installed with-in 100mm of a timber stud and plaster wall using a double steel heat-shield with air gaps, never heard on any of them burning down accidentally except in bushfire, so I would say it was safe.
 Perhaps the standards have become tighter, but that is not necessarily to say the old standards were unsafe. 
If it were my wall I would specify Compressed sheet and be very happy, 13mm compressed cement sheet is very heat resistant, not to be confused with ordinary cement sheeting like Hardieboard

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## Moondog55

Under the Building Code of Australia Compressed
Fibre Cement sheeting is deemed to be non-combustible.
When tested in accordance with Australian Standard AS
1530.3 the Early Fire Hazard Indices are as follows:
Ignitability Index 0
Spread of Flame Index 0
Heat Evolved Index 0
Smoke Developed Index 0  1  *Cut and pasted from the BCG website*

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## Gaza

> But we are not talking about a fire rated wall.
> Anyway fire rated plaster is only rated for ceiling use, had that particular issue in another life. Although i think there are some new products that are designed for walls, need to double check 
> If it were my wall I would specify Compressed sheet and be very happy, 13mm compressed cement sheet is very heat resistant, not to be confused with ordinary cement sheeting like Hardieboard

  Incorrect normal fire rated p/b can be used for walls or ceilings, 
compressed fibro does have fire ristant properties but fire rated plasterboard is cheaper even if you need two layers.  
You will need to check that 12mm Cfc is suitable.

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## Moondog55

Gaza I refer you back to post #11

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## Gaza

> Gaza I refer you back to post #11

  Does not rate to fire rating in terms of mins.  Only flame transfer ie will nnot catch on fire but will allow thermal transfer. Plywood also can be found that has low flame index. Some timbers ie ironbArk very low flame index.  
Under BCA it sets out the requirements as 
Structural adequacy / Intergity / insulation.  
For eg a 2hr fire rated wall system is two layers 13mm fire check each side of the studs.

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## Moondog55

Sorry GAZA but you have lost me on this one. 
In the application we are talking about a wall is either flammable or not. 
The question was about heat shields in front of flammable walls and we seem to have got side tracked. I think I'm going to call my local council and see what the Greater Geelong position is as this is something we need to fund if we decide to go with a wood fire ourselves

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## Moondog55

Well I just got off the phone with the Geelong building section.
New BCA documents were released on 01 May and they do not yet have copies, old standard was a 90mm masonry wall with 25mm air-gap which is pointless, you may as well just build a masonry wall.
Lovely woman is going to send me photo copies of the new document as soon as they arrive, what she did tell me tho is; as long as the fireplace is installed in accordance with manufacturers instructions it is OK and the ripple iron would be just a decoration, clearances would be to the original wall not to the ripple iron surface.
This woman just spent 20 minutes looking through the BCAs trying to find a definition of what constitutes a "combustible wall/surface" without luck and ditto for "non-combustible" wall and I thanked her for her effort.  
How are inspectors supposed to do their job properly if the information in the regulations is so hard to find??

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## goldie1

I'm getting a little confused here. I have a freestanding wood heater installed two years ago. I just got out the  
installation instructions from the manufacturer ( Australian) which state that the fire box to comply with AS etc etc 
must be installed a minimum of 150mm from a combustible wall surface at the rear and 300mm at the side 
and if placed diagonally across a corner the two back corners must be a min. of 75mm from a combustible wall 
surface. If the wall is lined with mini orb why should this change? 
Just read your last post Moondog which seems to state that it doesn't

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## Moondog55

hi goldie 1
The point of a heat shield was to be able to reduce clearances.
It seems as if the BCA has gone thru a few changes so rapidly that some sections do not make a lot of sense.
Just imagine tho that you had an antique pot belly stove you wanted to install in your lounge room, and to be compliant it needed 1500mm or more of clearance to a "Combustible wall" the use of heat shields should be able to reduce that distance to 100mm or so.
The OP can do whatever they like if they keep to the manufacturers installation instructions as the ripple iron is considered "Decoration" but it was common practice to use dual layers of steel sheet with dual 25mm air gaps when installing wood heaters.
Heat-sheilds work in the same way as the newer "Zero clearance" wood heaters; an air-wash keeps the outer skin of the heater from getting too hot by a combination of convective and radiative cooling, a heat shield keeps the inner skin , the one next to the combustible wall, cool from the same mechanism.

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## goldie1

Understood. Thanks

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## cherub65

Don't worry about the BCA to much, you need the AS/NZS 2918 [sorry cant find it]. 
Clearances for different materials are determined by testing in this standard, Then BCA minimums are used if not using AS

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## Moondog55

I have a very real problem with forking out that amount of hard earned cash just to do a little research on feasibility, like most on the forum I feel that if compliance with a standard is mandatory the information should be available FOC.

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## cherub65

I'm hearing you, we fork out considerable amounts of money just to keep up to date. Tradespeople  at least should have access to relevant information to perform there jobs to the standards.

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## r3nov8or

I've been following this one for a while, and it seemed logical that the box manufacturer is the one who needs to provide relevant clearance info in the installation guide, as they are the only ones who know how their boxes are built

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## Moondog55

While it may seem logical, sometimes the space available isn't there, that was and is the whole point of the low profile heat shields, sacrifice 50mm of wall space to gain 550mm of room space. Made sense and it worked 
This is one rule ( the 90mm masonry heat shield ) that simply makes no sense, OK I don't have access to the relevant Australian standard ( they cost too much money to buy ) but it seems like common sense and good building practice has been thrown out the doorway.
It would help a lot if there was a definition and description of "Non-flammable" wall that could be understood by some-one who does not have a degree in engineering.
No good having a performance based building standard if they won't tell you what the performance should be.

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## Kirsty B

Wow.  I just want to thank you all for your response to my post.  I have found the information very useful.

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## Moondog55

You probably got a lot more than you asked for, these threads and their daughter threads often take on a life of their own.
Your pictures of the finished project are expected.

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