Insulation in fireplace behind wood burning stove

[Kaymo]

Hi,
I have a wood burning stove installed in an old fireplace which works really well except that the fireplace back is the bare stone external wall - see pic below. We like the look of the stone fireplace but we lose a lot of heat to the outside. I currently have a piece of leftover underfloor heating insulation, with some radiator reflector foil behind the stove, and then the logs stacked up which provides reasonable reflection of the radiated heat and insulation but the logs (especially as they get drier) are a fire risk and the foil is unsightly.

I am looking for a way to insulate the fireplace area without completely losing the 'look' of the old stone fireplace. I considered external insulation but this would look terrible against the old sandstone exterior, then stacking the logs on the outside of the wall to give a limited exterior insulation but this goes against the advice of keeping the log pile away from the house. I am now looking at these http://shop.vitcas.com/vermiculite-fire-resistant-board-brick-effect-fire-proof-insulation-670-p.asp brick effect boards but the amount of boards I would need to fully insulate the back and sides of the fireplace alone would be about £300.

Are there any cheaper/better ways to achieve the insulation without losing the traditional look of the fireplace, or am I being unrealistic? Just seems that to spend £300+ is not cost effective as it would take me years to recoup that cost against the heating bills.

View media item 58919

 

[Jackrae]

Why bother, With a good going fire and all that wood stashed up the side and to the rear, you won't have a house in a few weeks.

Seriously, you have a fire waiting to start.

You can get fire resistant plasterboard (pink I think) , 12mm thick, which will do all you need. Cut to size and glue into position, then paint to whatever colour you desire. At least, that's what's behind mine and it shows no sign of distress.

 

[diynoob]

How much heat are you losing out of the back of the stove? I can run mine all day and the back wall is cool enough to touch because the stove throws all the heat out of the front and top.

Are the fire bricks in place around the back and sides of the inside of the stove? Maybe they need replacing. You can get them made out of the Vermiculite stuff in your link.

 

[Kaymo]

diynoob,
I measured the temp on the outside wall during the winter comparing the wall behind the stove and the same wall further away from the stove. I cant remember the numbers but it was significant enough for me to be concerned that I was losing a lot of heat from the wall. The fire bricks seem ok, and the issue with the wall heating up at the back was there since the stove was new. It might in part be the design as it was quite cheap stove, although apart from the stove putting heat out the back it has been good and have had for 2 years now

Jackrae,
As I said in my OP I recognised it was a fire risk and the wood has already been removed since the pic was taken. It was a temp experiment using wood that wasnt well seasoned to see if it made much of a difference to the heat passing to the wall and we only had the fire on when we were in the room while the wood was there. Thanks for the tip on the Fire resistant plasterboard, will look out for that.

thanks

 

[masona]

Do a search on cast iron fireback, bought mine from ebay £58, total 2 hrs driving to get this then I got the blacksmith to make a couple of feet stands and what a difference with the heat back into the room, you can even use a cast iron drains cover This way everything match with the stove and my marble wall panel behind the stove doesn't even get warm let alone hot

Cast iron fireback

• masona
• 10 Jul 2013
• 2

http://www.ebay.co.uk/bhp/cast-iron-fire-back

http://www.fireplacemall.com/blog/2013/05/choose-fireback-stainless-steel-cast-iron/

I also have a Ecofan, works well but not cheap!

http://www.youtube.com/watch?v=Wqw-Rw70Euw

Just found out you can buy difference fireback feet set, need to make sure the thickness of the panel will slot in.

Doh! just seen your Ecofan

 

[Kaymo]

Thanks Masona, that looks good, but my stove pipe comes out the back so it might be a bit tight against the wall. I had been thinking before though about some sort of metal reflector and what you have there looks a lot better than a flat sheet of metal. I have got an ecofan too and it does work well but back wall does still get quite warm.

 

[masona]

my stove pipe comes out the back so it might be a bit tight against the wall.

I reckon it's possible

If not, you could get made to measure custom fit etc

 

[Kaymo]

Hi,
I know its been a while since I started this post but I got pulled away from this project due to a number of other priorities such as the lath and plaster ceiling collapsing in the same room!

I found it really difficult to find much information on insulating behind a stove so I thought it might be useful to others in the future to update this. I looked at vermiculite insulation but this was way to expensive to offer payback in a reasonable amount of time so in the end I settled with Rockwool and cement board which are both A1 fireproof and relatively inexpensive. I found this link to be really good and was where they suggested the cement board but again I was surprised that there was no suggestions on insulation so I checked out the data sheets on rockwool myself to ensure that it was fully fireproof and would maintain its effectiveness against that level of heat.

http://www.stovefittersmanual.co.uk/articles/lining-a-fireplace/

The pic below shows the rockwool slabs cut to fit the back and above the stove and I have cut cement board to fit in front of this. The only question that I am still considering before I seal it all up and paint is whether this scenario would require a vapour barrier and I would welcome any thoughts on this? I am not sure how much vapour would pass through the cement board and if it did and there was some moisture reached the stone wall whether the sandstone and lime mortar would allow it to breathe, there is not anything there to rot as the insulation is straight on to stone and is tiled at the bottom.

View media item 70452 View media item 70453

 

[parisproctor]

Hi,

I have been looking to create a solution to this exact problem. We are still in testing phase however I have managed to reduce the thermal bridge by 50% and the composite panel I have made is only 13mm thick. I will share more info as and when I am able. Also looking at slightly thicker options in order to provide various routed patterns in the panel that will mimic stone or brick. The problem is definitely real as my wall shows!

Untitled

• parisproctor
• 19 Dec 2013
• 1

 

[Kaymo]

Hi Paris,
That's very similar to what I see on the outside, although I dont have a thermal image I used an IR thermometer last winter and and the full section of wall behind the fireplace was a good few degrees higher than the rest of the wall.

 

[Kaymo]

Hi all,
Happy new year!

Just following up on my above post about moisture barriers. Since my last post I left the insulation in place, and cut a concrete board and fitted in front of the insulation to about 1m up from the bottom. I pulled it all out again today and there is indeed a lot of moisture behind the insulation but the insulation behind the concrete board is fairly dry and the only moisture that is there appears to be dripping down from above. This is making me wonder whether fitting the cement board over all of the insulation and sealing any gaps with cement based mortar would provide a suitable vapour barrier? Does anyone know if moisture will permeate through cement and concrete?

The other option I am considering is to put a spacer in the back between insulation and the wall and a few holes through the cement/insulation at the bottom to allow some airflow behind the insulation to the stack, but I have very little space left to come out due to the flue so the most I could leave at the back of the insulation is about 10mm.

On the plus side (provided I can deal with the moisture issue), the last few weeks with the insulation against that wall has made a huge difference to the comfort levels in that room, even when the stove is off the cold draft that used to come off that wall is completely gone.

Thanks in advance for any comments.

 

[Blagard]

You can get fire resistant plasterboard (pink I think) , 12mm thick, which will do all you need. Cut to size and glue into position, then paint to whatever colour you desire. At least, that's what's behind mine and it shows no sign of distress.

That is bad advice

Plasterboards designed to give a fire rating are to protect the structure from collapse for 30/60minutes or whatever after which they will probably collapse themselves. They are not suitable for sustained exposure to high temperatures or for use in this situation. You are just lucky your situation may not be extreme enough to find out the hard way!

This explains it better
http://www.fahrenheitstoves.com/2013/02/17/pink-plasterboard-is-not-fireboard/

Noted the original posting is old but the issue is still current

 

[Kaymo]

Hi Blagard,
Thanks for the response but I haven't used plasterboard, I have used cement board, which is A1 fire rated, as is the insulation. I agree with you about the plasterboard.

My intent is to face off the insulation with cement board and paint the cement board as close to the Sandstone in the original fireplace as possible. There are no flammable materials my only remaining problem is the moisture and whether the cement board will be a suitable moisture barrier.