[Stoves] Building my Heat / cook stove.

Tue Feb 8 06:57:30 CST 2011

Hello Stovers,

     Spent some time working on the stove last week and things are 
beginning to take shape.

     You can see a basic diagram of what I'm working towards on the 
attachment to my mail to this group on 30th January.

     Some photos of things as they stand. -

     http://www.b-e-t.org.uk/uploads/images/firebox.jpg

shows the ceramic lined combustion area.  The gases will exit through 
the heat exchanger behind this and the fuel hopper will be to the left.  
You can just about make out the secondary air inlet here in the middle 
of the back wall, just above the ceramic block - the air will be flowing 
in through the box section you can see running across from the left 
through the fuel hopper. This runs across and then down to where the air 
will exit into the firebox.  This box is 20mm x 20mm ID.

***** Do people think this should this provide sufficient secondary air 
or should I put another similar secondary inlet in the front of the 
burner??? *****

The ceramic blocks are not fitted correctly in this picture.  Currently 
aiming for a 'throat' area of 10cm x 10cm

http://www.b-e-t.org.uk/uploads/images/choke.jpg

this shows the choke / bleed hole in the heat exchanger section.  We 
decided to make a sliding 'door' in channels that can be moved (between 
burns, by reaching down into the burner after lifting away the flue) and 
then wedged or welded into place when set right.  With this 'door' wide 
open the bleed hole is 5cm x 10cm

http://www.b-e-t.org.uk/uploads/images/top.jpg

Finally a poorly focussed top view that shows a bit more of the layout.

We decided to make the hopper smaller than on the diagram - if I 
remember correctly 20cm x 25cm.

My friend had a grate from an old coal stove that appeared to be a 
suitable size and we intend to use - from memory this grate is approx 
15cm x 20cm.  Thinking of having the 15cm side in front of the 10cm 
throat through into the combustion area.

If anyone has got any comments/ideas I'm hoping to get some more work 
done on the stove tomorrow (if I can correctly diagnose a spluttering 
Mitsubishi diesel engine today)

Also I had some questions below, to which some answers would help guide 
the construction process.

Best

Darren

On 30/01/2011 00:31, Darren Hill wrote:
> 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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