[Stoves] Converting a Chiminea into a Rocket Stove

[Kevin Chisholm]

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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