hearth help?!

[theoldship]

Hi everybody

 

I'm trying to install a Valor Arden stove into my boat. The manual says the stove must be placed on "a constructional hearth of non-combustible materials not less than 125mm (5") thick" Any ideas how I can achieve this or what I should use? I'll be replacing the stove with a bigger one before next winter and putting a new floor down and therefore new hearth, I'm still at the fit out stage, so it's only for the next few months that I need to get this one in for so I can carry on working on the boat, I just need a safe quick and cost effective solution for now. The footprint of the hearth would be 800mm by 700mm minimum but it's going in the middle of the boat so there's no need for a surround I literally just need something I can sit it on and bolt through. It doesn't have to look pretty as it will be gone in the summer just needs to be safe! I can't find a ce Mark on the stove for en13240 and nothing is mentioned of that in the manual. It's a 5kWh stove. Also I'm in the Uxbridge area if that might mean anything to anyone in terms of sourcing materials. Any advice would be greatly appreciated. Thanks all.

[cariad]

make a frame to the manufacturer's specification then fill it with concrete, place your fire on top, but make sure you put your fixing bolts in place while still wet.

when the time comes to break up the concrete and do a permanent job.

[Ally]

Agreed, framed concrete, keep it just below floor level but good sized, can then be tiled flush to the surrounding floor.

[rjasmith]

Before you start up the concrete mixer might it be worth giving Valor themselves a call and asking to speak to their Tech Dept?

 

When I was researching the installation requirements of our stove (a Hamlet Hardy 4) in the early days of the dreaded BS 8511 Code of Practice, I got a great deal of help from Richard Drake, Arada's Tech Director. Since then Arada seem to have put all their stoves through the EN13240 approval process. Maybe Valor have as well.

 

If you can get them to put in writing that an Arden is now approved, you can use any of the alternative hearth arrangements given in BS 8511. If so, perhaps the non combustible 12mm min. thick hearth material is all you will need, on top of a wood floor.

 

The 5" concrete job was of course originally lifted out of the Building Regs Document J (for houses) and caused a great deal of amusement when BS 8511 (for boats) first came out. Unfortunately, you are right that any of the much more sensible arrangements now included in BS 8511 can only be used if the stove is approved to EN 13240.

 

Richard

[Ryeland]

My Valor Willow on the boat gives very little heat downwards, I just have tiles on 3/4 ply with no problems.

 

Just for interest I have just put my hand under the Clearview 6KW stove at home and the tiles are just lukewarm!

 

I think the main reason for fireproof covering is in case of embers falling out of the stove. I think the 5" hearth in houses covers the old open fires which would get very hot.

 

Richard

[rjasmith]

My Valor Willow on the boat gives very little heat downwards, I just have tiles on 3/4 ply with no problems.

 

Just for interest I have just put my hand under the Clearview 6KW stove at home and the tiles are just lukewarm!

 

I think the main reason for fireproof covering is in case of embers falling out of the stove. I think the 5" hearth in houses covers the old open fires which would get very hot.

 

Richard

 

Hello Richard,

 

Yes the EN13240 test that's relevant to this is that the stove must not raise the surface temp of the hearth underneath it to greater than 100°C. If it can't pass this you need the concrete mixer!! (Or you can mount direct it on the steel hull - one of the better ideas in the later version of BS 8511!)

 

Richard

Edited January 11, 2014 by rjasmith

[Québec]

Ours is bolted onto a block of 25mm fireboard (same material as fire bricks) covered in slate tiles. Just had a BSS inspection. No problems.

[The Bagdad Boatman (waits)]

The 5 inch base is recommended for wooden flooring. Look out for a york stone slab which is good.

[theoldship]

Hi and thanks for all your replies. I've done a bit of research and pouring concrete seems beyond me. What I think I might do is securely screw my plywood floor down into it's bearers around where the hearth will go, and then screw into that a wooden frame into with I will neatly fit a sheet of 12.5 mm aquapanel cement board, on top of that will sit eight aerated concrete blocks, again neatly fitted to the frame, then top the whole thing with another sheet of 12.5 mm aquapanel screwed into the wooden frame and the stove will sit on that. I'll secure the legs of the stove by bolting them to two strips of steel angle which can be screwed to the wooden frame using brackets. The concrete blocks are A1 fire rated and are apparently good thermal insulation and the aquapanel is non combustible and combined will give me the 125mm thickness for the hearth that the manufacturer reccomends, and the wooden frame will be considerably further away from the stove than the manufacturers guidelines for the size of the hearth. I need to get the stove in as fast as possible but safely and I have most of the materials for this apart from the concrete blocks which are cheap, and there are no aesthetic considerations whatsoever it all be gone in the spring. What do people think of this plan?

[Bee]

Just a thought, if your `proper` stove has a backboiler and you run a gravity system from it you need to get the stove as low as poss. this makes sense anyway as it keeps your feet warmer. I cut a hole in the 3/4 ply floor and made a metal tray to sit in it, bit of cement and tiles and stainless trim and it looked good and it kept the stove nice and low and minimal contact with any wood etc.

[rjasmith]

Hi and thanks for all your replies. I've done a bit of research and pouring concrete seems beyond me. What I think I might do is securely screw my plywood floor down into it's bearers around where the hearth will go, and then screw into that a wooden frame into with I will neatly fit a sheet of 12.5 mm aquapanel cement board, on top of that will sit eight aerated concrete blocks, again neatly fitted to the frame, then top the whole thing with another sheet of 12.5 mm aquapanel screwed into the wooden frame and the stove will sit on that. I'll secure the legs of the stove by bolting them to two strips of steel angle which can be screwed to the wooden frame using brackets. The concrete blocks are A1 fire rated and are apparently good thermal insulation and the aquapanel is non combustible and combined will give me the 125mm thickness for the hearth that the manufacturer reccomends, and the wooden frame will be considerably further away from the stove than the manufacturers guidelines for the size of the hearth. I need to get the stove in as fast as possible but safely and I have most of the materials for this apart from the concrete blocks which are cheap, and there are no aesthetic considerations whatsoever it all be gone in the spring. What do people think of this plan?

 

Not worth giving Valor a call before doing all this then?

 

If they say they've had it approved then all you will need is one 12.5mm aquapanel sheet on the floor and you'll have a hearth that meets BS 8511!

 

If they can't then your solution above would seem fine to me and will be much easier to take apart later than a lump of concrete!

 

Richard

[SamKingfisher]

I mean, like, don't actually do it but pouring concrete is definitely not beyond you. It's one of the easiest jobs in the world. But don't do it, especially for a temporary install . . .

[bizzard]

If a sheet of industrial polythene is laid down on the floor first the concrete won't stick and can be lifted out. And there's always the trusty old paving slab, granite preferably. Dig one up in the high street.

Edited January 13, 2014 by bizzard

[theoldship]

Hi everyone

I've spoken to Valor who's only advice was to speak to a hetas engineer but when pressed about specifics they suggested I speak to Arada. They advised me that this model of stove was never tested to en13240 and that I would have to raise it 125mm from the wooden floor but that a wooden frame topped with something 12mm noncombustible with an air gap underneath would be fine which I'd be a lot happier with because then I could manually check how hot the floor was getting anyway. So now I'm thinking to build a wooden frame by putting four lengths of timber down screwed into the floor, one at each side of the hearth and two in the middle positioned underneath the legs of the stove so I could screw them into that. I could top this with the 12mm aquapanel I've got I'm just wondering if its solid enough/may crack? Any thoughts on whether this is a good plan and what a suitable 12mm material is, does it need to be tiled over etc.? Thanks

[stuart]

I personally would have used paving slabs to pack up the floor - if the stoves not approved, I wouldnt want to risk it. Aquapanel won't burn - but it still transfers heat to the other side, so don't get wood too close.

[theoldship]

Hi again

As I've now had sort of conflicting advice from valor, and then from Arada who said I have to raise the stove 125mm from a wooden floor but that I could achieve this by building a wooden frame with 12mm of noncombustible material on top of that which seems contradictory as large sections of that frame would have to be right under the stove to support it and therefore nowhere near 125mm away To follow valor's advice and build something that big out of concrete or similar for a 5kw stove to probably get just a couple of months use out of it seems ludicrous. I'm kind of out of ideas?!

[rjasmith]

Hi again

As I've now had sort of conflicting advice from valor, and then from Arada who said I have to raise the stove 125mm from a wooden floor but that I could achieve this by building a wooden frame with 12mm of noncombustible material on top of that which seems contradictory as large sections of that frame would have to be right under the stove to support it and therefore nowhere near 125mm away To follow valor's advice and build something that big out of concrete or similar for a 5kw stove to probably get just a couple of months use out of it seems ludicrous. I'm kind of out of ideas?!

Are you sure you've been talking to the real tech dept people at Valor/Arada? It's been my experience in the past that you can get put through to the "monkey" rather than the "organ grinder" on these occasions.

 

I don't know if Richard Drake is still part of Arada (who are the firm that are behind quite a few stove product names, ie they manufacture Aarrow, Hamlet, Stratford and Villager. These makes are not separate companies at all. I didn't think Valor was one of theirs but perhaps they've told you that they are?

 

Richard used to be the Arada Tech Director so a big wheel but I think he may be semi retired now and is just their consultant. It would be worth trying to get chapter and verse from him if you can. If it helps, I think I may have an email address for him and could PM it to you.

 

In my case, I was originally going for an Aarrow Acorn 4 but at the time Richard told me that they hadn't got this approved. However he said their Hamlet Hardy 4 is an identical stove and had been approved! In the end I bought the Hamlet with it's shiny "CE" plate on the back and will be installing it on a bit of 25mm vermiculite board with quarry tiles on top. All of this is fixed straight on the plywood floor and will easily meet BS 8511. The floor will have 4 coach bolts poking up through it to take care of the anchoring of the stove feet.

 

Since then (about 2 years ago) Arada have also got the Acorn range approved which is why I thought it might be worth checking more carefully re the Valor Arden.

 

Don't forget the EN 13240 test checks to see that the stove can't heat its hearth up to more than 100°C. If you can get the firm to put that in writing for you (even if they haven't actually done an official test) you would be home and dry. Richard did that for me originally before I decided to go for the Hardy which turned out to be cheaper than the Acorn anyway in a deal being promoted by a local store!

 

Richard

Edited January 14, 2014 by rjasmith

[theoldship]

Thanks for your advice Richard

The people at Arada said the stove definitely didn't comply with en13240 so can't go down that route, I think I'll follow the guidelines on the soliftec guide and use calcium silicate board that I'll get from midland chandlers, with an air gap underneath and cement board and tiles on top. At least then I'm following someone's guidelines, and to my mind that amount of insulation plus an air gap underneath will be safe. Would still like to hear any advice or opinions on this generally, and any tips on cutting and fixing calcium silicate board.

Thanks all

[Barry]

I think the 5inch thick base is recommended for houses where the floor is wood or the hearth is supported by wooden joists.

 

It is a fire prevention measure.

 

As such if you have nothing flammable below your stove you could lay slabs on top top of the metal bearers in your bilge and it would be fine. You could stand the thing on bricks if you wanted

[rjasmith]

Thanks for your advice Richard

The people at Arada said the stove definitely didn't comply with en13240 so can't go down that route, I think I'll follow the guidelines on the soliftec guide and use calcium silicate board that I'll get from midland chandlers, with an air gap underneath and cement board and tiles on top. At least then I'm following someone's guidelines, and to my mind that amount of insulation plus an air gap underneath will be safe. Would still like to hear any advice or opinions on this generally, and any tips on cutting and fixing calcium silicate board.

Thanks all

 

Annoyingly for you, the only reason they say it isn't compliant is probably because they haven't paid TUV or some other test house to have the test done! Looking at a picture of the stove, I bet it would pass the hearth heating test because it's legs are quite a bit longer than the ones on my Hardy 4. Perhaps there are other aspects of 13240 that they suspect it won't meet and hence don't want to bother with doing the approval. I see that the Valor website says the Arden is "not available at the moment" - perhaps they're redesigning it - is it actually made by Arada for Valor?

 

I think the calcium silicate board from MC is something called Super Isol or Skamolex Blue which is a board made in Scandinavia somewhere. I got some from the sole importer 2 years ago before it was more generally available. It's the board with the lowest thermal conductivity figs given in BS 8511 and is ideal for the fire surround but not really good for a hearth as it's not got great strength in compression. Compressed vermiculite board might be better for that and is what I'm using. Maybe MC keep it as well? The Soliftec Boat guide drawing says use "sturdy non flammable" board for the hearth, not Calcium Silicate! You need to be a bit careful with that guide, it's good and full marks to Soliftec for allowing everyone to see it for free but it only shows the "popular" bits of what is in BS 8511 and not all the possible approved ways of doing things. Unfortunately seeing a copy of BS 8511 is either expensive or difficult!

 

Although air gaps are good, again the Soliftec drg expects them to be used on the surround, not the hearth where the stove needs support as well as the fireproofing.

 

Bazza's suggestion is good - can you cut a bit of your wood floor out and put your "sturdy non flammable" hearth stuff straight on to the hull steel framing underneath. You might need a few extra bits of steel bolted to the frames to help take the weight of the stove legs perhaps and provide fixing points, plus a few bricks as well maybe? When you get the later (approved?) stove you could replace the cut out floor section and make a new simpler hearth in accordance with Soliftec/BS 8511 ie 12mm thick minimum non combustible material on top of the replaced wood.

 

Finally - it's very easy to cut Super Isol! Just use any old wood saw. It's not unlike plasterboard in consistency but without any paper on the surfaces. It is not strong at all and is why the smallest available thickness is 25mm.

 

Richard

Edited January 14, 2014 by rjasmith

[dor]

Coming a bit late to this one...

 

I'm not actually familiar with the stove in question; what is it - a blast furnace? 5 inches of concrete!

 

As what you are looking for is just a temporary measure, I would think a concrete slab on the floor would be fine. Restrain it with some wooden strips round the sides screwed to the floor or drill through the slab and screw it to the floor. Assuming the legs of the stove have holes in for screws like most stoves, then drill and plug the slab and screw the stove to the slab to satisfy requirements that the stove shouldn't move. Surely this will satisfy the BSS examiner? If you haven't got enough of the hearth extending in front of the stove you can have a separate piece of fireproof material on the floor which doesn't have to be fixed down.

 

My hearth is a 30mm slab of stone fixed to 4x2 bearers with silicone and four screws. Stove is screwed on two legs through slots in the stone to the bearers underneath. This satisfied the picky surveyor who oversaw my RCD compliance and has satisfied two BSS examiners since.

 

You just don't get that much heat directed downwards - plenty of people dry their kindling by putting it under the stove!

[blackrose]

Coming a bit late to this one...

 

I'm not actually familiar with the stove in question; what is it - a blast furnace? 5 inches of concrete!

 

As what you are looking for is just a temporary measure, I would think a concrete slab on the floor would be fine. Restrain it with some wooden strips round the sides screwed to the floor or drill through the slab and screw it to the floor. Assuming the legs of the stove have holes in for screws like most stoves, then drill and plug the slab and screw the stove to the slab to satisfy requirements that the stove shouldn't move. Surely this will satisfy the BSS examiner? If you haven't got enough of the hearth extending in front of the stove you can have a separate piece of fireproof material on the floor which doesn't have to be fixed down.

 

My hearth is a 30mm slab of stone fixed to 4x2 bearers with silicone and four screws. Stove is screwed on two legs through slots in the stone to the bearers underneath. This satisfied the picky surveyor who oversaw my RCD compliance and has satisfied two BSS examiners since.

 

You just don't get that much heat directed downwards - plenty of people dry their kindling by putting it under the stove!

 

I was beginning to think it was just me who thought it was a bit over the top (along with some of the advice given in this thread!)

 

My 9kW stove sits on a sheet of 8mm masterboard which is tiled over. I remember at the time some people were telling me that I didn't need masterboard under the stove, just behind it, but I did it anyway. Now they're saying you need 5" of concrete or massive slabs! I don't now what sort of stoves other people have but my stove doesn't throw much heat downwards.

 

Anyway, if they're saying you have to put 5" of concrete below the stove, what thickness of fireproof material would you have to put behind it - 2ft?

Edited January 15, 2014 by blackrose

[Barry]

Coming a bit late to this one...

 

I'm not actually familiar with the stove in question; what is it - a blast furnace? 5 inches of concrete!

 

As what you are looking for is just a temporary measure, I would think a concrete slab on the floor would be fine. Restrain it with some wooden strips round the sides screwed to the floor or drill through the slab and screw it to the floor. Assuming the legs of the stove have holes in for screws like most stoves, then drill and plug the slab and screw the stove to the slab to satisfy requirements that the stove shouldn't move. Surely this will satisfy the BSS examiner? If you haven't got enough of the hearth extending in front of the stove you can have a separate piece of fireproof material on the floor which doesn't have to be fixed down.

 

My hearth is a 30mm slab of stone fixed to 4x2 bearers with silicone and four screws. Stove is screwed on two legs through slots in the stone to the bearers underneath. This satisfied the picky surveyor who oversaw my RCD compliance and has satisfied two BSS examiners since.

 

You just don't get that much heat directed downwards - plenty of people dry their kindling by putting it under the stove!

 

 

 

I was beginning to think it was just me who thought it was a bit over the top (along with some of the advice given in this thread!)

 

My 9kW stove sits on a sheet of 8mm masterboard which is tiled over. I remember at the time some people were telling me that I didn't need masterboard under the stove, just behind it, but I did it anyway. Now they're saying you need 5" of concrete or massive slabs! I don't now what sort of stoves other people have but my stove doesn't throw much heat downwards.

 

Anyway, if they're saying you have to put 5" of concrete below the stove, what thickness of fireproof material would you have to put behind it - 2ft?

 

I think the minimum 5" thick hearth stems from the days when there were open fires in each room in a house. On the upper floors in almost all cases, and on ground floors in some cases, the floor construction was wooden joists or beams supporting a floor layer which could also be wooden. The hearth would be constructed with a layer of stone or concrete and the fireplace surround placed on top of that. The fuel grate would thus be a short distance from the hearth.

 

There were many cases of house fires caused because the hearth was too thin, or cracked. the heat from the fire set fire to the floor structure beneath the hearth, setting fire to the house

Edited January 15, 2014 by Bazza2

[Rob@BSSOffice]

Ours is bolted onto a block of 25mm fireboard (same material as fire bricks) covered in slate tiles. Just had a BSS inspection. No problems.

 

The BSS would not check this matter of the thickness of the hearth.

 

The only relevant check for BSS examinations is that the stove must be secure e.g. foot bolts or side brackets etc.

[rjasmith]

Unfortunately, those of us referring to more exotic hearth arrangements than it would seem to others to be necessary are only quoting from the dreaded BS 8511 Code of Practice that was produced about 3 years ago by BSI in response to a request made by the MAIB inquiry following the Lindy Lou fire which involved a fatality. Please don't shoot the messengers!!

 

Remember (and this is only my understanding having taken an amateur interest in the whole process of producing BS 8511) that this document was not sponsored by the Boat Safety Scheme and as Rob says, most of its requirements are not part of a BSS inspection. However BSS do refer to it and recommend it as good practice.

 

Nor does BS 8511 have anything to do with the RCD requirements, in fact NONE of the RCD ISO standards even mention a solid fuel stove (they do have one that covers general fire safety but it is not specific to solid fuel).

 

When BS 8511 first came out, it was clear that the drafters had plagiarised much of the Building Regs Document J that covers houses, not boats! This is why the famous 125mm concrete hearth got put in it, causing not a little derision from people like me who sent in comments! What was worse was that the drafters had not even copied the Doc J drawing correctly!!

 

It still appears in the final version now but only applies if you have a non approved (to EN 13240) stove and don't want to use one of the other alternative (much easier) hearth suggestions that were added later.

 

As I suggested in an earlier post, many stoves have now been approval tested so we KNOW they can be put on a 12mm non combustible hearth on top of eg wood instead of just guessing that it will be OK! Unfortunately insurance companies may not go along with a guess when you claim after a fire!

 

Richard