[Stoves] Heat / cook stove - proposed design

[Darren Hill]

Hello Crispin,

     Thanks very much, once again for the detailed response...  
responses and a few more questions in your text....  Also latest design 
attached.

On 29/01/2011 04:10, Crispin Pemberton-Pigott wrote:
>
> Dear Darren
>
> Based on the hopper size, and presuming you have about 4 metres of 
> chimney,
>

If the chimney was shorter what would be the effect?  I know less draft 
but how would that effect the fire in practical operation?  difficulty 
lighting?

> that size is probably going to be enough air to heat a home. Do you 
> have a kW rating in mind? I think you should be able to get 40 kW from 
> it. Do you want that much?
>

No - 4kw would be enough most of the time!!  I picked the stove 
dimensions in a fairly arbitrary way - what felt right (based upon ?) + 
the space I have available.  I'm happy to modify to suit.

> *>>*The area of the hole should be about 30 x 120mm.
>
>
> The primary air hole should be 30x120mm?  With a valve so its adjustable?
>
>  The hopper should have no air leaks into it at all.  I hope you saw 
> the stove from Eastern Canada that Kevin passed around. That top was 
> good -- it had a woven seal.
>
My friends has been constructing fire-in-a-metal-box stoves for some 
years and most of her customers have wanted air tight stoves that they 
can fuel-up and then shut-down so that they are still alight in the 
morning.  Shes got plenty experience making air tight doors
>
> >>Lastly, constrain the entrance into the combustion area (where the 
> secondary air enters) to about 1/3 of the area of the hopper. Keep it 
> square-ish, definitely not long and thin as is often seen in furnaces.
>
>
> >You mean the 'throat' from hopper (A) to combustion area (B).  Third 
> of the hopper width >would be about 7cm.  7x7 then?
>
> No, a third of the area, not a third of the dimension. If you have 20 
> x 30 cm = 600 cm^2 then 1/3 = 200 cm^2 = about 140 x 140. My little 
> model says 14.5 x 14.5 but that is a bit big, just looking at it 
> (subjective opinion). If you only want 20 kW, meaning a max of 20 and 
> sometimes 4, make the constriction smaller, say 100 x 100mm. That 
> constriction is perhaps 100 to 125mm above the lower end of the grate, 
> just as you drew it.
>

I dont need anything like the KW ratings you are suggesting here.  The 
20x30 hopper was as big as I thought I could get away with in the space 
I have available.  I was thinking of the amount of fuel I could fit in 
the hopper and the time it could burn between refuelling.  I think 4 kw 
output would be fine for me, possibly a bit more occasionally.

Am I better reducing dimensions more than we are talking here?
Throat?
Hopper area? -which I guess is also the grate area? - or do I not want 
the entire floor of the hopper to also be a grate?

> About the bricks, you can use any bricks. Go for the hardest, 
> strongest bricks you can find, if you can't get genuine low thermal 
> expansion materials. Put them in a way so that when they crack they 
> don't fall out of place.
>
>
My friend has a few spare bricks bricks she 'rescued' from a disused 
cement kiln - shes got some in the bottom of her coke fired blacksmiths 
forge and they've not cracked yet.

Actually I should have mentioned something before about the termination of
the grate on the left (lower) end.

It really should extend farther under the combustion area. The grate will
never really get covered by ash and char, so it lets air enter the gas
stream at the bottom end (part of the secondary air not coming through the
secondary air port I mentioned before).

>>>Changed on image.  Far enough??

I like the angle shown. We made it movable perhaps 15-20 mm left-right by an
external ring (which can be hooked and moved by a lot of convenient tools).

>>>  Is this to loosed up the coal?  Is this necessary/advantageous for a wood stove?

The divider between the combustion chamber and the hopper will get really
hot.

>>>  I'm going to try to use Ceramic blocks.

There is a stove called the Kitchen King made in Pretoria that uses a
similar secondary air entry method but places it as the hopper/fire divider,
passing the air into the gas stream as it goes under the divider. The
advantage is that the part gets really hot but remains an 'air cooled' part
= longer life.

>>>  If for some reason I cant make the blocks work I'll try something like this, although I guess from your previous descriptions it would be best if the secondary air did not join the combustion here.  I could have it ducted through this part though.



Oh, yeah, what is your chimney height?

>>>  As short as I can get away with....  Will insulated stack pipe help?  Thinner?


Thanks again

Darren

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