There are well over 1,500 woodstove models to choose from. Which one you select will remain largely a matter of personal preference: but do check that the manufacturers’ suggested rates of heat output are compatible with the heat required in your house. Also, a cast iron stove will last longer than one of thin sheet steel; 6mm steel plate should, however, last as long as cast iron. As with all equipment, the simpler the stove, the less chance there is of a breakdown. A simple pivot draught control should last as long as the stove (fifty to a hundred years for cast iron); but electric fan assisted heat transfer may be an unnecessary and complicated addition.
It must be emphasised that by replacing part of your central heating system with a wood-stove you will not be helping to reduce the national domestic consumption of energy. All you will be doing is hastening the day when the meagre wood resources of some countries are finally exhausted – unless sustainable forestry policies are aggressively pursued. The only way to reduce energy consumption is to insulate the building, for example by lining walls and sealing off draughts.
Once you have insulated your house you can consider the best way to heat it. A woodstove will save energy if it replaces an open fire: when coal or wood is burned in a grate, 80 per cent of the energy contained in the fuel is lost up the chimney. In a closed wood-burning stove only 40 to 50 per cent of the available energy is lost up the chimney. This also compares well with a central heating system where maybe 40 per cent of the energy is lost.
Demolition sites are good sources of waste wood, which would otherwise be burnt without doing more than warm the hands of a few building workers. In managed forests you can find trimmings and slab wood (the bits with bark on one side which are cut off to square the log prior to sawing). Slab wood is often burnt on site at sawmills as it would be a fire risk if stored in large quantities. The estimated two million tonnes of waste wood produced each year in the UK could be used to heat 5 per cent of houses if these were properly insulated. It is no good burning waste wood in a picturesque log fire, whether such a fire is the only source of heat in a draughty cottage or a conversion piece in a centrally heated home. From the point of view of energy consumption, the only efficient thing to do is to burn wood in a long lasting, closed wood-burning stove.
Selecting the right model
Some of the most efficient stoves available in the UK are the airtight box stoves: these consist of a sealed container to hold the wood with an adjustable air inlet to control the rate of burning. Copies of the original Scandinavian designs are also now being manufactured. Of these, the taller models with extra baffles provide longer pathways for the hot flue gases before they go up the chimney. This both ensures more complete combustion of the wood and gives a greater area of hot metal to radiate heat to the room. A stove run with the door open, and there are combination stoves which can be either open or airtight, will consume more wood per kWh of heat emitted into the room than an airtight stove; running a stove with the door open so that you can see the flames is not going to save energy. The only thing to be said against the more efficient airtight stove is that when it is burning on its lowest setting creosote forms on the inside of the flue, and this could lead to a chimney fire; so the chimney should be swept regularly.