[Stoves] Building my Heat / cook stove.

[Crispin Pemberton-Pigott]

Dear Darren

 

First the cast iron grate is about right for the 4 kW (average, not peak)
power you want. I have been trying to make a 4 kW stove that burned clean
and the whole grate area is about 155 x 220 after discounting the parts that
are hiding under shields. What matters is the volume of coal or wood burning
at once. That sets the power level.

 

I just want to confirm that the bleed hole takes hot fire gases from the top
of the combustion area into the flue before they go down into the heat
exchange, in other words like a GTZ 7.5 (now to be called a GIZ 7.5 after
their name change).

 


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



Actually I can’t see it clearly. How big is it?


>With this 'door' wide open the bleed hole is 5cm x 10cm



That is easily large enough.


>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.



The whole grate does not need to be under the combusting zone. About ½ is
correct to give a crossdraft through the bottom of the fuel in the hopper.





>>Based on the hopper size, and presuming you have about 4 metres of
chimney, 


>If the chimney was shorter what would be the effect?  

 

Power is related to the draft, taller chimney means more draft means more
power. You can choke it of course with a damper.


>The primary air hole should be 30x120mm?  With a valve so its adjustable?



Yes. If you are quite short, it will be obvious in the thermal efficiency
number because too much excess air (secondary air oversupplied) will give a
cool burn and a high Stack EA (= low efficiency).


>Shes got plenty experience making air tight doors



 Good!

 

The Hopper size:

>Am I better reducing dimensions more than we are talking here?
>Throat?
>Hopper area? 

 

You can easily slim the hopper by dropping clay slabs inside it to narrow
it. Ditto with the grate actually.

 

>- or do I not want the entire floor of the hopper to also be a grate?



Yes, almost. As the air is not rising into the hopper other than enough to
get over to the combustion area, making it too small or too much tucked
under the combustion area will limit the power, maybe to the point of it not
working well. In your drawing you have the grate nicely angled but stopping
before it got under the combustion area. With the angled grate extending
from under the hopper (except perhaps the bit at the very front) to the back
of the combustion area (the flame runs vertically from there) you can make a
crossdraft fire that is adjustable across a pretty good heat range.


Perhaps you can make a good drawing in cross section of what you have now.

 

Regards

Crispin

 

 

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