Multifuel Stove in Conservatory through polycarb roof - doable

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I have a 4Kw multifuel stove, brand new with certificate I am planning to put it in my conservatory & I have a few questions on both the method & legality before I make the final decision whether to do it or not.

I have been reading about the special flashing kits that enable the twin wall flue to exit straight up through a polycarbonate roof - this is the method I was contemplating, here are the details:
  • The stove will be against a cavity concrete block/brick wall (not PVC framework)
  • 4Kw output multifuel stove with a 5" flue outlet - both top & rear
  • The roof is 35mm Polycarbonate.
  • The distance from the flue exit to the wall of my house would be approx 3.5 metres
  • Distance to next door's wall even further, however very close to the wall of next door's outhouse
  • there is a vent fitted in the conservatory if required?
  • The flue could go through the wall using the rear exit on the stove, but obviously this involves more work, tools & materials

So based on the information above is it do-able? if so how tall would the flue need to be on exit to meet regulations?

How far from the wall would the stove need to sit (it is a plastered/emulsioned wall)

Would the twin wall flue have to be stainless steel?, or any twin wall?

Finally I am a very experienced multi-disciplined DIY'er with over 20 years experience (and no disasters!) basically If I can't do a job to a high standard I won't do it, so basically I am planning to do the installation myself is this permissible?, I believe you can do the installation yourself then contact your local authority to get it inspected & certified etc is this correct?, if so what would be the cost of having this done.

Any help or advice much appreciated

Thanks in advance
 
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Yes, it can be done, but it's a bit of a faff. Even twinwall flue gets hot, so you need to make sure it's far enough away from the roof to avoid any thermal effect. I've not come across any twinwall that isn't stainless and is rated for use on a solid fuel appliance. I don't know what else might be used.

Minimum flue length is 4.5 metres. You need to think carefully about how you're going to both support the weight (which can't be borne by the stove) and prevent it falling over in the wind. Rear exit - max distance is 100mm horizontal before going vertical, so unlikely you'll be able to use this.

The stove installation manual should tell you how far from surfaces it needs to be. Is it plaster on block, or dot&dab plasterboard skimmed over? If it's the latter, it's considered to be combustible and a suitable heat shield will be required.

You also need to consider the hearth, especially with regard to what the floor is made from. If it's timber, it'll need cutting out and a constructional hearth of at least 125mm thickness will need to be installed.

Some local authorities will inspect and sign off DIY installations, others won't. Contact yours to ask before you start work. They'll be able to tell you what their fee is. It's unlikely to be cheap.
 
Thanks for the reply

it's a concrete sub-floor, covered with laminate.

It looks more work than I first imagined, I'm probably not going to bother, as it's only an occasional /weekend use room anyway.

I read somewhere as the outside wall of my house is greater than 2.3M from the stove, the flue only has to be taken up 1M above the roof of the conservatory - is this correct? or rubbish/outdated. Also, as long as the twin wall flue is vertical with no bends (which it would be) a minimum length of 3.5M is permissable with modern flue systems

Also, as long as it's a non-combustible sub-floor, you can mount a suitable hearth of a minimum thickness of 50mm on the wooden floor? again fact or fiction.

Thanks
 
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No, all incorrect I'm afraid. 4.5m is the minimum height, regardless of what's around it or whether it goes straight up.

Fiction on the hearth too, generally speaking. You'd need to cut out a minimum of an 840×840mm square from the laminate and sit your hearth on that. The only exception to that rule would be if your stove carries a manufacturers certificate saying that its base will not exceed 100°C in use. If it has such a certificate then it can be mounted on a 12mm thick non combustible hearth, which could be glass if you want to keep the wooden floor effect under it
 
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Thanks,

Yes I can cut a square out of the Laminate easily & sit the hearth directly on the concrete sub floor, that wouldn't be a problem at all. The wall is currently papered - but the paper can be removed easily, or could I just use a heat shield?. How far from the wall will the stove need to be?. I believe the wall is just concrete block plastered over

The outlet of the stove to the roof inside is approx 2m - so as the distance from the flue to the wall of my house is greater than 2.3m I would only need the remaining 2.5m minimum length on the outside that correct? if so that wouldn't be to bad, so I may do it still. I'm just looking into what is involved in applying for a building notice certification from my local authority.
 
You could use a heat shield. The clearances to walls and other surfaces will be detailed in the stove's installation instructions or available from the manufacturer. Correct on the external flue but you do need do consider how you're going to support the weight and stabilise it against the effects of wind. It's normally only self supporting up to about 1-1.5m depending on the brand
 
Do you have enough wall space above the back of the stove to fit a base support bracket to carry the weight of the flue?
I guess a pic or sketch of your layout may be helpful ?
 
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Here is a photo of where I propose to put the stove, I can confirm the wall is concrete block, plaster boarded over & skimmed. The height from the flue exit on the stove to the roof is approx 2M. Obviously everything will be removed off the wall, including the dado rail + wallpaper if required
 

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Aside from any height issues and supporting it outside, the Power outlets and skirting have to be considered.
Whats within the stove manufacturers distance to combustables to the left of your proposed position.
As well as making allowances for flue manufacurers distance from that roof rafter you have to fit a suitable flashing ,if theres any capping over a sheet joint you may need to move flue to the left of it
 
Yep, you'll probably need to move those sockets & cut the skirting back, you'll definitely need to fit a heat shield to the wall, and you can't put the flue brackets on the plasterboard as they'll push through it over time - you'll need to cut through to the block. Might be easier to cut a section of plasterboard away floor to ceiling then get it hardwalled instead.
 
Thanks,

The Manual & plate on the back of the stove state 800mm from the rear & 600mm from the side away from combustible materials, which is obviously too far out from the wall - so I would have to remove the
sockets/skirting board & the plaster board & hard wall it, fit a heat shield & then I could have it closer to the wall? 600mm from the side isn't an issue I don't think.

Removing the sockets, skirting board, paper etc isn't a problem, but I assume I would have to remove the plasterboard aswel?

Can someone advice me on 'hardwall' how is it done & what would be involved - I'd certainly need the help of a tradesman here as I cannot plaster myself
 
You wouldn't need the heat shield with hardwall. The heat shield is there to protect combustible materials, such as your plasterboard, which has a nasty habit of catching fire on the side that faces the wall if it gets too hot. Seen that happen once, first they knew of a problem was smoke pouring out of the eaves...

Hardwall - cut out existing plasterboard to 600mm either side of stove, floor to ceiling. Spread hardwall on to the bricks / blocks. Do magicky plastering things to make it look smooth. Probably skim over the top. Heat resistant skim is available from Vitcas. They do a render too, which you could use instead of the hardwall.
 
Thanks, yes that all sounds very do-able without too much work, yes I'm going to do it!. The water pipes will go too, as it feeds a radiator just to the right of the stove wall that won't be needed with a stove (I can always stick an oil filled electric rad in it's place if no solid fuel burning required on spring/autumn days)

I can put a flue support straight into the concrete wall, and supporting the remaining 2.5M flue out the roof is do-able too I'm sure.

Still not looked into notifying my local authority regarding the inspection & certification - i.e. the cost compared to get a proper company to install it?

Even if I do get a company to install, I can still do alot of the work myself, such as cutting the floor, supplying & fitting the hearth, removing all combustible materials etc
 
Hi yes It came with a very detailed certificate with tests for both (as it's multifuel) I'll post cert on here tomorrow
 

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