Testing of stoves involves determining how much fuel is used to perform various tasks. The reason for the interest in fuel and stove efficiency is that most fuel used in stoves in biomass (mostly from trees and bushes). This fuel has to be collected by someone, usually women and children. If a stove that can burn less fuel is affordable and convenient to use, people switching to a fuel-saving technology can save time collecting fuel. This stretches the existing resource and saves labour.

Some stoves are specifically designed to burn small diameter fuel which can be described as 'kindling'. The small branches of bushes and scrubby trees frequently have such fuel as a significant proportion of their total wood mass. This fuel is frequentl left on the ground when people collect firewood as it is not deemed to be a very useful fuel. In some countries it is the only fuel available but it is burned in a very wasteful fashion in open fires.

The Viro Stove is designed to burn wood up to 110mm in diameter and up to 200mm long. It has three provisions for secondary air, two of which are controllable.combining It has preheated primary and secondary air. Nearly all the available heat contained within the biomass fuel can be liberated. It also means there there is less smoke, particulate matter and Carbon Monoxide (CO) emitted, compared with most other stoves and open fires.

The Viro Stove is constructed from a custom made 25 litre paint can. It has two grooves in the sides which provide support for components at certain points. This allows for the stove parts to be nested for shipment and later assembled without welding. There is a top deck which supports the pot rest, two air controllers, a secondary air preheating tube and a basket-type fire grate. Inside the top section there is a flame shield to protect the outside top of the stove from heating up too much and to reflect the flame's heat back to the pot. The pot (up to a No. 4 cast iron three legged pot or any flat bottomed pot up to 230mm in diameter) sits inside the upper section to receive maximum heat transfer and to shelter from the wind.

The primary and secondary air control levers slide horizontally. The air supply to the fire is closed modulated so that there is enough primary air to pyrolize the fuel at a rate commensurate with the power demand and enough secondary air to burn the biomass gases completely. This gives significant control over the fire's heat output while simultaneously becine able to cope with a wide variety of fuels (from wood to dung) and still have a good emissions rating.

The average fuel load is between 300 and 1200 grammes of wood.
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