<div dir="ltr"><div class="gmail_default" style="font-size:small">Good question, Robert.</div><div class="gmail_default" style="font-size:small"><br></div><div class="gmail_default" style="font-size:small">Other sizes work. 25x25x25 cm works well with maize stalks in home kitchens. We recommend 45x45x30 for school kitchens for more firepower.</div><div class="gmail_default" style="font-size:small"><br></div><div class="gmail_default" style="font-size:small">Different sizes may work better depending on the fuel and cooking needs. 25x25x25 seems to be a good general recommendation since we train on a mass scale and cannot customize based on the specific needs of a family or community.</div><div class="gmail_default" style="font-size:small"><br></div><div class="gmail_default" style="font-size:small">Squared holes work best with stacked fuels like maize stalks. For a 25x25x25 hole, the stalks should be cut to about 23 cm and stacked in crisscrossing layers. This method seems to get the most fuel in the hole while allowing air to circulate within the pile. Cylindrical holes would work better for fuels like wood shavings and cow dung patties.</div><div class="gmail_default" style="font-size:small"><br></div><div class="gmail_default" style="font-size:small">Generally, the area across the top equals firepower and depth equals burn time. 25x25 area across the top gives good heat with maize stalks. If the depth is more than 25 cm, the fire goes out before the bottom fuel burns.</div><div class="gmail_default" style="font-size:small"><br></div><div class="gmail_default" style="font-size:small">Denser fuels burn longer. For example, normal size firewood burns over three hours in a 25x25x25 hole. This is much longer than needed. We will put common bricks in the hole to raise the floor, reduce the burn time and save fuel.</div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Wed, Jun 22, 2022 at 1:17 AM Robert Taylor <<a href="mailto:rt@ms1.hinet.net">rt@ms1.hinet.net</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div>
<font face="Microsoft JhengHei UI">Hi Kevin<br>
<br>
Very interesting. What's the significance of the hole size and
shape, 25 x 25 x 25 cm? Is it optimal for good combustion, or
simply convenient based on pot size and fuel quantity?<br>
<br>
Best regards<br>
<br>
Robert<br>
</font><br>
<div>On 22-Jun-22 5:13 AM, K McLean wrote:<br>
</div>
<blockquote type="cite">
<div dir="ltr">
<div class="gmail_default" style="font-size:small">
<div class="gmail_default">Adding a 25x25x25 cm hole to
traditional open-fire cookstoves may end the collection of
firewood from forests in many areas. By piling fuel in the
hole beneath the cookpot and lighting the pile on the top,
the fuel burns long, hot, with no tending and with less
smoke. And by quenching the embers, cooks make biochar.</div>
<div class="gmail_default"><br>
</div>
<div class="gmail_default">We found that most woody biomass
bigger than thin twigs burns well in the <a href="https://youtu.be/DmzQFCp2kNI" target="_blank">cooking hole</a>. Firewood the
size that is typically burned in unmodified three stone
cookstoves burns for three hours without tending. Much less
smoke is emitted than from an unmodified three stone
cookstove. A colleague estimates that the amount of wood in
the cooking hole would burn for 30-40 minutes in an
unmodified three stone cookstove. Here's a <a href="https://drive.google.com/file/d/15V4vTJxO1Lcm0wFzB96pQT9jvgjaXkwh/view?usp=sharing" target="_blank">video</a>. </div>
<div class="gmail_default"><br>
</div>
<div class="gmail_default">Thick twigs burned without tending
for 1.5 hours. Thick twigs and small branches are abundant
and unused in much of Africa.</div>
<div class="gmail_default"><br>
</div>
<div class="gmail_default">The cooking hole also works with
crop waste (maize stalks and cobs, cassava stems, banana
peels, bean stems, ...), elephant grass, bamboo, large
sawdust and wood shavings, sawdust briquettes, dung patties
and more. Depending on the fuel, the fire will burn without
tending for 20 minutes to several hours. Here's our <a href="https://youtu.be/DmzQFCp2kNI" target="_blank">training
video</a>.</div>
<div class="gmail_default"><br>
</div>
<div class="gmail_default">Women can:</div>
<blockquote style="margin:0px 0px 0px 40px;border:none;padding:0px">
<div class="gmail_default">- All but stop collecting
firewood.</div>
<div class="gmail_default">- Leave the kitchen to do other
things once they start the fire.</div>
<div class="gmail_default">- Make biochar.</div>
</blockquote>
<div class="gmail_default"><br>
</div>
<div class="gmail_default">And 8-12 common bricks can support
two cookpots over one cooking hole allowing two meals to be
cooked with the same amount of fuel and time it takes to
cook one meal. The time to boil is only a few minutes
longer than for one pot.</div>
<div class="gmail_default"><img src="cid:18189cf675efccc1bfb1" alt="2
burner drawing.jpg" style="outline: 0px; margin-right: 0px;" width="338" height="263"><br>
</div>
<div class="gmail_default"><br>
</div>
<div class="gmail_default"><br>
</div>
<div class="gmail_default">In much of Africa, most people know
how to make bricks. We show them how to make free custom
bricks to line the cooking hole. Here is a <a href="https://drive.google.com/file/d/1b2WvePKX_ofnELUWhexqQZR4NyCrXxnH/view?usp=sharing" target="_blank">video</a>.</div>
<div class="gmail_default"><br>
</div>
<div class="gmail_default">Kevin McLean</div>
<div class="gmail_default">Sun24</div>
</div>
</div>
<br>
<fieldset></fieldset>
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