[Stoves] Converting a Chiminea into a Rocket Stove

Fri Dec 29 10:08:01 CST 2006

Dear Ken
----- Original Message ----- 
From: "Ken Boak" <kenboak at stirlingservice.freeserve.co.uk>
To: "Discussion of biomass cooking stoves" <stoves at listserv.repp.org>
Sent: Friday, December 29, 2006 11:34 AM
Subject: Re: [Stoves] Converting a Chiminea into a Rocket Stove

> Kevin,
>
> Thanks for the advice.
>
> I am already using a PC radial  blower fan for forced draught -

If you think that is impressive, try a high speed jet of air. Wowsers!! :-)

but I
> regularly light barbeques in the Summer with a hot air gun - and ideal
> source of hot draught.

If your chain saw has a single point of exhaust discharge from teh muffler, 
that is an impressive way to goose up a smaller fire. If you want "awesomely 
impressive", use a leaf blower.
>
> I'm doing some temperature logging tests to see how well the litte stove 
> heats the room.  The room is only 8' x 9' x 8 ' ceiling - so 4kW should be 
> more than ample.

If you just want to be practical, then stick with the PC fan. :-)
>
> I was taught, time, temperature and turbulence are the best ways to 
> improve
> combustion, and the little PC fan is certainly causing the products of
> combustion to whip around the inside of the globe like a cyclone and
> hopefully heat up the outer casing.

Try for central placement of fuel, and true tangential introduction of PC 
air.
>
> The main problem is that almost all of the stove is "buried" within the
> brickwork of the firplace aperture, not giving much of an opportunity to
> re-radiate into the room.

Can you fashion a damper with a hole in it, that would prevent "room air" 
from drafting up the chimney, while at teh same time, providing an outlet 
for the strove gases? It would probably be even more effective to increase 
heat transfer area by installing a 6" diameter elbow and horizontal flue 
pipe, prior to chimney entry.
>
> I really need on of the low cost boxwood stoves from Vogelzang (Northern
> Tools)  which would stand fully proud of the fireplace brickwork.
>
> http://www2.northerntool.com/product/796_796.htm
>
> However, as we pay in pounds in the UK, for what sells for dllars in the 
> US,
> I am happy to continue my experimentation with my "gift horse" stove.

Having to work within the confines of an existing fireplace certainly 
imposed space constraints.

Best wishes,

Kevin
>
>
> Happy New Year,
>
>
> Ken
>
> ----- Original Message ----- 
> From: "Kevin Chisholm" <kchisholm at ca.inter.net>
> To: "Discussion of biomass cooking stoves" <stoves at listserv.repp.org>
> Sent: Friday, December 29, 2006 2:56 PM
> Subject: Re: [Stoves] Converting a Chiminea into a Rocket Stove
>
>
>> Dear Ken
>>
>> The 4 kw output would require in the order of about 3 CFM of combustion
>> air.
>>
>> If you want to have some impressive fun, get a vacuum cleaner, and 
>> operate
>> it in reverse, as a source of pressurized air. (Put the hose on the 
>> vacuum
>> cleaner discharge.) Typically, they are about 10 CFM at 10" static
>> pressure.
>> Get a length of 1" black iron pipe, 3' or 4' long, threaded on one end 
>> for
>> conventional pipe fittings, and duct tape it to the vacuum cleaner hose.
>> Drill out a cap or plug to give a jet passing about 3 cfm, and introduce
>> the
>> air tangentially above the grate. This is how to make a Tornado Stove. 
>> :-)
>>
>> Be careful that the cast iron does not get hot enough to melt, or to 
>> cause
>> a
>> radiant fire hazard.
>>
>> Please report back on your results. Pictures would be appreciated.
>>
>> Best wishes,
>>
>> Kevin
>> ----- Original Message ----- 
>> From: "Ken Boak" <kenboak at stirlingservice.freeserve.co.uk>
>> To: "Discussion of biomass cooking stoves" <stoves at listserv.repp.org>
>> Sent: Friday, December 29, 2006 10:23 AM
>> Subject: [Stoves] Converting a Chiminea into a Rocket Stove
>>
>>
>>> List,
>>>
>>> I have aquired a cast iron Chiminea stove which I have installed into 
>>> the
>>> open fireplace in my study room.
>>>
>>> The Chiminea, is a 14" diameter sphere, fitted with a 6" dimeter chimney
>>> approximately 8" long.  There is a 10" diameter grate placed in the base
>>> of
>>> the globe, and access is through a front aperture approximately 8" in
>>> diameter.
>>>
>>> The spherical shape appeals, as it provides the maximum internal volume
>>> to
>>> surface area ratio, so that the heat flux reaching the outer cast shell
>>> can
>>> be quite high.
>>>
>>> These Chimineas are sold cheaply across the UK at garden centres and
>>> intended to be used as patio heaters for outside use.  They  probably
>>> originate from China.
>>>
>>> One thought is to provide a rocket type fuelling tube near the front of
>>> the
>>> grate, to increase the velocity of the draught.
>>>
>>> I have been experimenting with using the Chiminea as a heat source for 
>>> my
>>> small study room.  The Chiminea fits neatly into the brick built
>>> fireplace
>>> opening  16" wide x 16" deep x 26" tall. The flue pipe of the Chiminea
>>> goes
>>> directly up the existing brick chimney - an estimated 16 feet tall.
>>>
>>> My intention is to try to retain as much heat in the brickwork
>>> surrounding
>>> the stove, so that it might re-radiate into the room.  The cast iron
>>> casing
>>> of the stove gets fairly hot and also re-radiates into the room -
>>> although
>>> it woyld brobably benefit if the stove body was not so enclosed in the
>>> fireplace aperture, but stood forward of the chinmey - sadly not 
>>> possible
>>> because of the vertical fluepipe connection.   In terms of size and 
>>> power
>>> output, the chiminea is probably about the same as the smallest of the
>>> commercial cast iron pot-bellied stoves, about 4kW.
>>>
>>> Initial tests have shown that currently much of the heat is lost 
>>> directly
>>> up
>>> the flue, and flames have been observed emerging about 6 to 8" above the
>>> top
>>> of the flue pipe.  This is probably because there is no baffle within 
>>> the
>>> stove, and  therefore no restriction to the exhaust gases.
>>>
>>> It should be quite simple however to create some sort of internal 
>>> baffle,
>>> to
>>> encourage the products of combustion to swirl in the flue area, and thus
>>> improve the retention time and also the heat transfer to the cast iron.
>>> It
>>> may also be possible to allow some secondary draught to allow secondary
>>> combustion in the upper hemisphere of the stove, thus reducing the
>>> flammable
>>> gases that go straight up the flue.
>>>
>>> Another idea is the provision of a stainless steel cylinder shaped 
>>> basket
>>> to
>>> allow the burning of woodchips.
>>>
>>> Many ideas to try out, and it will be good fun keeping warm whilst
>>> experimenting.
>>>
>>>
>>>
>>> Happy New Year
>>>
>>>
>>> Ken
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
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>>>
>>
>>
>>
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>
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>
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