Larry Winiarski's Rocket Stove Principles
Dean Still, April 2002

Dear Friends,

I was typing up Larry's latest simple stove principles for Aprovecho's

newsletter, "News From Aprovecho", (two to three times a year, $30/year,

describes activity, I'm editing number 59) and thought I'd send it along.

Reflecting on the Rocket I might point out a interesting point: no secondary

air. I've tried adding heated secondary air into the top end of the internal

chimney above the combustion chamber but haven't noticed an improvement in

amount of smoke or in fuel efficiency. I ended up thinking that enough

primary air is left at the top of the combustion zone anyway. Adding air may

just reduce temperatures. I'll test this further with better equipment.

The Rocket stove is trying to create supportive conditions for complete

initial combustion which seems to pretty much work when the right amount of

fuel is introduced. The added draft created by the insulated chimney above

the fire pulls in lots of air, which like a fan, makes a hotter, vigorous


Anyway, here are Larry's principles of stove design:



Rocket Stove Principles

Dr. Larry Winiarski

Technical Director

Aprovecho Research Center

1.) Insulate, particularly the combustion chamber, with low mass, heat

resistant materials in order to keep the fire as hot as possible and not to

heat the higher mass of the stove body.

2.) Within the stove body, above the combustion chamber, use an insulated,

upright chimney of a height that is about two or three times the diameter

before extracting heat to any surface (griddle, pots, etc.).

3.) Heat only the fuel that is burning (and not too much). Burn the tips of

sticks as they enter the combustion chamber, for example. The object is NOT

to produce more gasses or charcoal than can be cleanly burned at the power

level desired.

4.) Maintain a good air velocity through the fuel. The primary Rocket stove

principle and feature is using a hot, insulated, vertical chimney within the

stove body that increases draft.

5.) Do not allow too much or too little air to enter the combustion chamber.

We strive to have stoichiometric (chemically ideal) combustion: in practice

there should be the minimum excess of air supporting clean burning.

6.) The cross sectional area (perpendicular to the flow) of the combustion

chamber should be sized within the range of power level of the stove.

Experience has shown that roughly twenty-five square inches will suffice for

home use (four inches in diameter or five inches square). Commercial size is

larger and depends on usage.

7.) Elevate the fuel and distribute airflow around the fuel surfaces. When

burning sticks of wood, it is best to have several sticks close together,

not touching, leaving air spaces between them. Particle fuels should be

arranged on a grate.

8.) Arrange the fuel so that air largely flows through the glowing coals.

Too much air passing above the coals cools the flames and condenses oil


9.) Throughout the stove, any place where hot gases flow, insulate from the

higher mass of the stove body, only exposing pots, etc. to direct heat.

10.) Transfer the heat efficiently by making the gaps as narrow as possible

between the insulation covering the stove body and surfaces to be heated but

do this without choking the fire. Estimate the size of the gap by keeping

the cross sectional area of the flow of hot flue gases constant. EXCEPTION:

When using a external chimney or fan the gaps can be substantially reduced

as long as adequate space has been left at the top of the internal short

chimney for the gasses to turn smoothly and distribute evenly. This is

tapering of the manifold. In a common domestic griddle stove with external

chimney, the gap under the griddle can be reduced to about one half inch for

optimum heat transfer.