of floors, hearths, woodburners, and heat 'loss'

[tycarregydwr]

We are preparing for our woodburner, finally, at last, allelulia, etc. We are getting a small wood-fired range (with an oven), in the living room. The house had concrete floors poured probably in the 1960s/70s, and a hideous tiled fireplace installed, which we have ripped out (lots of smashy fun!). We had lengthy talks with the stove installer as to the hearth. His initial suggestion was that we should insulate the hearth, possibly with celotex, rather than 'waste' energy heating the slab. Then he changed his mind and said it's probably not necessary with a cooker, since they throw the heat more upwards anyway. So we haven't bothered. We've laid a slate tile hearth over the concrete, the tiles are quite thin so it's only about 1/2" above the concrete slab.
This week I visited friends in their (completely and utterly amazing) G2 listed pre- and Georgian mansion, in the kitchen they have thick slates and an aga (electric). The slates were warm underfoot for quite a radius around the range, and purely as a result of it - no underfloor heating.

So my question to those of you with cold solid-ish floors and range cookers is, does the floor warm up and, is this a good or bad thing?

The stove installer said it would be a 'waste', but I'm thinking, if some of the energy goes into the slab then surely that's just the slab acting as a heat sink/thermal mass, and therefore no bad thing?

 

[Andrew Bodenham]

tycarregydwr,

Your 'stove installer' is coming up with some 'interesting' suggestions there. I'd point him towards the Building Regulations and Approved Document J which gives details of typical hearth constructions, and clearly states that all the materials under or near an appliance should be non-combustible. Is Celotex considered non-combustible for this application? I certainly wouldn't want it in any part of a hearth or fireplace construction.

As you rightly say there's no such thing as 'waste heat' if it's all going into the thermal mass of the house. Ideally your floor slab would have an insulation layer below, but I'd not worry about it at all. Our woodburners sit on tiles on concrete and eventually everything warms up nicely.

 

[Stevie816]

Hi Ty
Can I call you Ty ?
Just get a modern stove from a reputable manufacturer not a cheap chinese one.
These are so efficient and can safely burn all night . and make sure your chimney is safe, it may well require lining We recently upgraded our 30 year old Jotul stove to a clearview and are amazed at it's performance. If your chimney is on an outside wall then concider moving it away from the wall further into the room. Most modern stoves can have a back flue.
Steve

 

[tycarregydwr]

Well his suggestion was to put down celotex and then put our slate tiles over that which would have completely encased it in non-combustible material. But I'm glad we didn't bother!
He is aware of all regs I'm sure and has been keen to do everything else by the book (we have to remove a section of poorly installed plasterboard that is too close to the stove site, and he gave us all the necessary dimensions of the hearth with regards to distance from the front of the stove). He's just very keen on maximising efficiency from wood heat, hence his slight obsession with insulation.
He comes extremely highly recommended by pretty much everyone I've spoken to in the area including 3 conservation builders, and I've seen his work in 8 houses plus his own, so I trust him.

Thanks for your reply, I've happy with how it looks and it was definitely less work this way!

 

[Penners]

My very inexpert option is that the lack of insulation in the construction hearth is not worth worrying about. We all know that hot air rises, so the majority of the heat from your stove (cooker or not) will head upwards. A small amount of radiant heat will tend to warm the hearth, but I don't believe that any significant amount of this will actually be lost - most of it will, as you suggest, just be stored in the concrete heat sink and given off when the stove cools down at night.

Yes, you'll probably find that the floor nearest the stove will become warm, but I don't believe this effect will extend very far into the room.