What's the difference between multi-fuel stoves and wood burners?

Firstly, you need to understand the difference between burning wood and burning multi fuels such as anthracite or smokeless coal. To burn effectively a smokeless coal fuel load needs combustion air delivered from underneath, whereas a wood fuel load doesn’t and only needs an air supply from above. These differences are reflected in the way that wood burners and multi fuel stoves are made.

Multi Fuel Stoves

Since smokeless coal requires combustion air (known as primary air) from below then a multi fuel stove must feature an open or partially open fire grate in the base of the fire chamber that lets this air pass through. Primary air supply is usually controlled by a slider or knob positioned towards the bottom of the door and is used to manage the flame pattern and burn rate of the smokeless fuel load. To stop coal ash blocking the air passages in the fire grate and starving the fuel of combustion air the fire bed should be riddled to encourage ash to fall into the ash pan below the fire grate. For convenience some multi fuel stoves feature an external riddler which allows you to riddle the ash without opening the door.

To burn wood efficiently a supply of combustion air delivered from above the fuel load is needed. This is called secondary air and its supply is controlled by a slider usually at the top of the stove, just above the door. Generally there is no need to use the primary air control when burning wood, except perhaps to boost the combustion air supply at the beginning of firing to ensure a quick start, after that the wood fire should be controlled solely by operating the secondary air control with the primary air closed off. There is no need to riddle the wood ash either. Having two separate air controls for the two types of fuel gives you maximum control over how effectively each burns and many people choose multi fuel stoves because of this fuel choice flexibility, even though they generally do not choose to exercise it, tending to stick with the fuel that they like best. Some stove manufacturers produce multi fuel fire grates that can be simply closed for wood burning and which can also be used for external riddling (for example Charnwood and Dunsley Heat).

Wood Burning Stoves

Given that wood really only needs combustion air delivered from above (secondary air) and doesn’t require its combustion air arriving underneath the fuel load (primary air) a true wood burning stove generally will not have an open fire grate, but instead feature a plain steel or vermiculite fire chamber floor. There is no need for an ash pan either as it is important to allow the wood ash to quickly build up to create an ash bed that will not only help the wood to burn more efficiently but will also provide a heat reflecting barrier to prevent damage to the stove base. There is therefore also no need for an external riddler. As always there are exceptions and some wood burners may still feature a small open grate and an ash pan for ease of cleaning whenever the bed of ashes needs to be removed. On older wood burning stove designs, again there are two separate controls for primary and secondary air and in such situations the primary air control is used to boost the combustion air supply for speedier lighting, The fact that most wood burners have no fire grate, no fire grate carrier frame and no ash pan tends to make them cheaper than the equivalent multi fuel stove version. In some cases, Charnwood being the best example, if you ever change your mind a multi fuel innard set for the appropriate wood burner can be bought as an option and retro fitted very easily.

NB It’s worth pointing here that many modern stoves, whether they are wood burning or multi fuel, feature single user-friendly air controls which have been designed to supply the correct mix of primary and secondary air ideally suited to wherever you are in the burn cycle and whatever fuel you are burning.