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Hello Crispin,<br>
<br>
Thanks very much, once again for the detailed response...
responses and a few more questions in your text.... Also latest
design attached.<br>
<br>
On 29/01/2011 04:10, Crispin Pemberton-Pigott wrote:
<blockquote cite="mid:009501cbbf6a$768afd50$63a0f7f0$@gmail.com"
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<p class="MsoNormal"><span style="font-size: 11pt; font-family:
"Calibri","sans-serif"; color: rgb(31,
73, 125);">Dear Darren<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family:
"Calibri","sans-serif"; color: rgb(31,
73, 125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family:
"Calibri","sans-serif"; color: rgb(31,
73, 125);">Based on the hopper size, and presuming you have
about 4 metres of chimney, </span></p>
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</blockquote>
<br>
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? <br>
<br>
<blockquote cite="mid:009501cbbf6a$768afd50$63a0f7f0$@gmail.com"
type="cite">
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<p class="MsoNormal"><span style="font-size: 11pt; font-family:
"Calibri","sans-serif"; color: rgb(31,
73, 125);">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?</span></p>
</div>
</blockquote>
<br>
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. <br>
<br>
<blockquote cite="mid:009501cbbf6a$768afd50$63a0f7f0$@gmail.com"
type="cite">
<div class="WordSection1">
<p class="MsoNormal"><span style="font-size: 11pt; font-family:
"Calibri","sans-serif"; color: rgb(31,
73, 125);"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family:
"Calibri","sans-serif"; color: rgb(31,
73, 125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><b><span style="font-size: 10pt;
font-family: "Tahoma","sans-serif";
color: windowtext;" lang="EN-US">>></span></b><span
style="font-size: 11pt; font-family:
"Calibri","sans-serif";">The area of the
hole should be about 30 x 120mm.</span><o:p></o:p></p>
<p class="MsoNormal"><br>
The primary air hole should be 30x120mm? With a valve so its
adjustable?<br>
<br>
<span style="font-size: 11pt; font-family:
"Calibri","sans-serif"; color: rgb(31,
73, 125);"> 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.</span></p>
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</blockquote>
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<br>
<blockquote cite="mid:009501cbbf6a$768afd50$63a0f7f0$@gmail.com"
type="cite">
<div class="WordSection1">
<p class="MsoNormal"><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family:
"Calibri","sans-serif"; color: rgb(31,
73, 125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family:
"Calibri","sans-serif"; color: rgb(31,
73, 125);">>></span><span style="font-size: 11pt;
font-family: "Calibri","sans-serif";">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. </span><o:p></o:p></p>
<p class="MsoNormal"><br>
<span style="color: rgb(31, 73, 125);">></span>You mean the
'throat' from hopper (A) to combustion area (B). Third of the
hopper width <span style="color: rgb(31, 73, 125);">></span>would
be about 7cm. 7x7 then?<br>
<br>
<span style="font-size: 11pt; font-family:
"Calibri","sans-serif"; color: rgb(31,
73, 125);">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.<br>
</span></p>
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</blockquote>
<br>
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. <br>
<br>
Am I better reducing dimensions more than we are talking here?<br>
Throat?<br>
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?<br>
<br>
<blockquote cite="mid:009501cbbf6a$768afd50$63a0f7f0$@gmail.com"
type="cite">
<div class="WordSection1"><span style="font-size: 11pt;
font-family: "Calibri","sans-serif";
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<p class="MsoNormal"><span style="font-size: 11pt; font-family:
"Calibri","sans-serif"; color: rgb(31,
73, 125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family:
"Calibri","sans-serif"; color: rgb(31,
73, 125);">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.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size: 11pt; font-family:
"Calibri","sans-serif"; color: rgb(31,
73, 125);"><o:p> <br>
</o:p></span></p>
</div>
</blockquote>
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.<br>
<br>
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<pre wrap="">
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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