Green Building Forum - Square stove in corner - how close to solid plastered wall without risking blowing?

Square stove in corner - how close to solid plastered wall without risking blowing?

greenfinger — Mon, 31 Jul 2023 13:30:15 +0100

Hi all

We're looking to have a wood stove installed. It will go into the corner of a room, at 45 degrees to the walls. Both walls are external, cavity, with plastered block / brick on the inside.

One installer has said so long as the two back corners are 100mm minimum from the walls, there won't be a problem with blowing the plaster.

But another has said it is best to follow the stove guidelines for distances to combustibles (even though the wall isn't combustible; but to prevent blowing) - which in our case would be 400mm.

Quite a difference! Would anyone mind sharing your thoughts on which sounds most realistic?

Many thanks

Square stove in corner - how close to solid plastered wall without risking blowing?

owlman — Mon, 31 Jul 2023 18:33:53 +0100

If aesthetics or flue outlets are an issue are an issue and you'd prefer the stove further back but are worried. Then you can always fit some FR board into the corner and finish the top and leading edges with a SS channel as required.

Square stove in corner - how close to solid plastered wall without risking blowing?

Mike1 — Mon, 31 Jul 2023 21:14:24 +0100

What does the manufacturer say about the distance to non-combustible materials? Treat that as a minimum and add more according to your risk tolerance.

Square stove in corner - how close to solid plastered wall without risking blowing?

WillInAberdeen — Tue, 01 Aug 2023 10:51:06 +0100

https://www.stovefitterswarehouse.co.uk/pages/rules-for-wood-burning-stoves answer probably here

NB the distance from the flue pipe to the wall might also be an issue, unless it is the bulky twin-wall kind?

FR board is only good for an hour or two of resistance, if you need a heat shield it would have to be steel with an air gap behind it.

Square stove in corner - how close to solid plastered wall without risking blowing?

greenfinger — Tue, 01 Aug 2023 11:12:29 +0100

Many thanks for the replies. The manufacturer says 150mm to non-combustibles. But seeing as it is only the stove corners that would/might be less, and the majority of the stove would be more than 150mm, I wondered if 100mm (from the back corners) might be enough. Furthermore, in the past the manufacturer have said that because it is not a "requirement" as such, it is ultimately down to the installer. As above, two installers have wildly different thoughts on this.

But perhaps I should see if I can make 150mm minimum work to be on the safe side...

Thanks for the link @WillInAberdeen. That was useful, as most of his articles are.

I was going to ask about whether there is some kind of THIN fireboard that can be applied directly to the boards without an airgap (and the painted the same colour as the wall to help it disappear), but based on the post above, and the article in the link, it looks like that doesn't exist.

Thanks again

Square stove in corner - how close to solid plastered wall without risking blowing?

WillInAberdeen — Tue, 01 Aug 2023 12:28:04 +0100

Should have mentioned, I had to look into this because the previous owner of our place had DIY installed a stove and the separation distances are a bit short to comply. We asked a couple of guys to sweep the chimney, they said they couldn't touch it because it's not compliant and they would have to condemn it. Just to bear in mind that in future you might have someone round with different opinions from the original installer!

Square stove in corner - how close to solid plastered wall without risking blowing?

owlman — Wed, 02 Aug 2023 11:37:21 +0100

Posted By: greenfingerMany thanks for the replies. ..............

I was going to ask about whether there is some kind of THIN fireboard that can be applied directly to the boards without an airgap (and the painted the same colour as the wall to help it disappear), but based on the post above, and the article in the link, it looks like that doesn't exist.

Some boards like Hardibacker @ 12mm are about the thinnest. Vermiculite boards, some with decorative patterns for painting, can be bought from 16mm upwards. Thinner than those it'd be fibreglass mesh and FR plaster.

Square stove in corner - how close to solid plastered wall without risking blowing?

Mike1 — Wed, 02 Aug 2023 12:41:28 +0100

Posted By: greenfingerFurthermore, in the past the manufacturer have said that because it is not a "requirement" as such, it is ultimately down to the installer.

I'm a bit rusty in this area, but I seem to recall that if the manufacturer's 'recommendations' aren't followed, then the minimum distances in Part J of the Building Regulations apply instead. I don't recall it being left to the opinion of the installer. But maybe someone else can chip in on that?

Square stove in corner - how close to solid plastered wall without risking blowing?

GreenPaddy — Wed, 02 Aug 2023 15:14:50 +0100

If the manuf says 150mm to non-comb, I would stick with that. That happens to be the same number as building regs. I'm guessing you're in England, so it will require a self certified installer (HETAS??), [or else notify building control and go that route], and so they will have to follow the regs, or manuf requirements if more arduous. Make it 150mm perp to the stove sides, which will end up with the corner closer to the perp dist from the wall. Check the stove sides and back min dist, not always the same.

If you go closer than 150mm, then your walls need to be 200mm thick.

As above, the flue (if uninsulated) needs to be at least 3 times the flue diam from any combust materials, which can sometimes be the determining factor, but since your wall is non-combustible block of more than 75mm, then ingore that.

Read Part J of the building regs (Section 3.17 onward in Scotland). You'll likely end up with more understanding than your installer. There are lots of details in the regs for a stove install (understandably), and I've seen enough new installs that don't comply, to make double checking any installer worth while.

Square stove in corner - how close to solid plastered wall without risking blowing?

greenfinger — Sun, 06 Aug 2023 17:54:31 +0100

Thanks for all the additional replies, much appreciated.Â Â

I think once we've decided on our stove (new thread coming up to help with that), I'll speak to the manufacturers about distances to non-combustibles, risk of plaster cracking, minimum distances for good airflow, etc.Â And I'll discuss it with the installer as well.Â Â

I'm hoping we won't have to do anything.Â But if we do I guess my favoured option would be to fix some thin fire rated board to the walls around the stove, and paint them in the same colour as the walls to help disguise them.Â If that's not sufficient, then perhaps remove the plaster in the necessary areas, get the walls back to brick/block, and then replaster with Vitcas type stuff *OR* use the thin fire rated board,Â fixed directly to the brick/block.Â Â

With regards building regs, I've read in several articles that there aren't any which reference minimum distances to non-combustibles. If that's wrong, would you mind letting me know what the regs say (or which section it is, so I can look it up)?

Thanks again

Square stove in corner - how close to solid plastered wall without risking blowing?

GreenPaddy — Mon, 07 Aug 2023 15:58:14 +0100

Document Part J, pages 36-42. Interestingly (for me) having followed these guidelines (& Scottish equiv) for many years, it seems that there is some uncertainty in my reading of the regs. You can ignore the 150mm appliance to edge of a wall abutting hearth requirement, if the wall is masonary/conc of thickness given in a table. The Scottish Regs explicitly state this. The Eng/Welsh regs don't, a little more interpretation.

Every day is a school day

Square stove in corner - how close to solid plastered wall without risking blowing?

djh — Mon, 07 Aug 2023 21:25:16 +0100

Posted By: GreenPaddyYou can ignore the 150mm appliance to edge of a wall abutting hearth requirement, if the wall is masonary/conc of thickness given in a table. The Scottish Regs explicitly state this.

But what if the wall is plastered?

Square stove in corner - how close to solid plastered wall without risking blowing?

greenfinger — Tue, 08 Aug 2023 00:42:32 +0100

Posted By: djh
But what if the wall is plastered?

From my limited understanding it doesn't make a difference. Plaster is still counted as non-combustible. It can crack and blow but I don't think that is covered by the regs as I guess it is cosmetic? More than happy to be corrected though!

Posted By: GreenPaddyDocument Part J, pages 36-42. Interestingly (for me) having followed these guidelines (& Scottish equiv) for many years, it seems that there is some uncertainty in my reading of the regs. You can ignore the 150mm appliance to edge of a wall abutting hearth requirement, if the wall is masonary/conc of thickness given in a table. The Scottish Regs explicitly state this. The Eng/Welsh regs don't, a little more interpretation.

I'm in Wales, and have stupidly just been looking at the "For use in England" doc. Will have another look at the For use in Wales doc in the morning.

But from what I've read so far regarding distances to non-combustible walls, only p.42 applies. And for my situation, where the hearth will indeed abut the wall, my understand is that:

- If the stove is less than 50mm from the wall, the wall needs to be 200mm+ thick.
- If the stove is between 51mm and 300mm fro the wall, the wall needs to be 75mm+ thick.

Does that sound about right?

Next... how to work out how thick my inner leaf of wall is! Although that being said, for good airflow alone I wouldn't want the stove less than 50mm away, which puts me in the walls @ 75mm+ thick camp, which I'm hoping I easily meet.

Many thanks