|Home||Electricity efficiency||SolarPV systems||Gas consumption||Wood burning stoves|
Experiences with a wood burning stove
|In a bid to reduce gas consumption in my home, I
installed a wood burning stove in my main living room. This is a 5kW stove
(Westfire Uniq 15, a Danish make) in which only wood should be burned. It has
an 84% efficiency rating, which makes it one of the most efficient and far more
efficient than a traditional open fire (which tend to be more like 30%
efficient as most of the heat goes up the chimney). It comes with a five year
warranty. Supplied as an optional extra, I fitted a duct to the outside wall to
avoid air being taken from the room.
Other types of stove - sometimes with an adjustment - permit smoke-free coal or wood to be burned. I was not interested in using coal as this always has to be bought.
This and other versions of stove are available with soapstone tops or surrounds. This warms up during use and realise the heat gradually while the stove is still cooling. However, they are significantly more expensive and I was advised by my suppliers that soapstone was not worth the additional cost.
Heating the roomMy living room is unusually large (10.5 metres by 3.5 metres) so I was interested to know how quickly it would heat up. The following chart illustrates how the temperature builds up in two different parts of the room. Although under specified for the size of my room, the Westfire 15 does a good job but is best when the fire is lit well before nightfall.
Heat from the stove rises and, in the absence of other drafts and circulation, heats the room from the ceiling downwards. I found that the temperature at chair level was significantly lower than the temperature experienced 1.8 metres higher. In the large draft free room, the air was not circulating enough to mix the heated air with the colder air at floor level. Therefore I experimented using old computer fans to create a small airflow in different parts of the room. The tests weren't extensive but they suggested that, although stimulating more air movement may be important, a fan needs to produce a more powerful airflow than could be produced by these small, quiet fans (see chart above).
Using a stove fan to improve air circulationStove fans claim to improve air circulation and thereby also reduce fuel usage, so I bought one to experiment. These sit on top of the stove, get hot and use a thermocouple to create electricity to drive the fan (see photograph). They come with two or three fan blades.
Although these work (in the sense of spinning and throwing warm air forward), they are expensive (about £160) and I'm not convinced that they have created much extra air circulation other than immediately above the stove. My tests will continue this winter.
However, they are quite fun and a great talking point for curious visitors!
Is a wood burning stove cost effective?Stoves are expensive to buy and have installed. Installers are able to charge a fortune because the stove and flue installation must comply with building regulations. Installation costs can be double the cost of the stove. Given this, their running costs need to be low for them to be an attractive financial investment. Their running cost is mainly determined by the price of firewood.
It is too early for me to predict accurately how much wood I need through a winter season, particularly as it is not yet particularly cold. I'm burning through about 1 'trug' full (15-18kg) every 1.5 days from late afternoon through the evening. When the temperature falls I'll need to light the stove at the beginning of the day and even then it won't heat the whole house sufficiently. Wood consumption might rise to 2 'trugs' per day or more. If I assume about 12-16 'trugs' per 'bulk bag' (250-290kg per bulk bag) then from October to March I would need approximately 5-6 tonnes of wood per year (ie 23 bulk bags or 365 trugs). At £100-£200/tonne that's £500 - £1,200 per year (or £2.75-£6.60 per heated day).
5-6 tonnes equates to about 7.5-9 cubic metres of stacked wood (it depends on whether it is soft or hard wood). My current stack (see photograph) amounts to 3.4 cubic metres so I would have to restack these shelves at least twice a winter.
Last year I estimate my gas bill for space heating was £470 (see my Gas Consumption page); lower than average because I was using the wood burning stove casually. If I assume it would have been twice this without the stove, £940, that's almost mid way between the £500 - £1,200 I estimate for the cost of wood. (This is consistent with other research which suggests that wood burning is comparable to gas heating in terms of £/kWh.)
If I have to pay for the wood, the stove, its installation, regular cleaning and maintenance, then a simple wood burning stove does not seem a financially attractive alternative to heating by gas central heating. Since heating by electricity or LPG are more expensive than gas, wood might be an attractive alternative in that case. Of course, if I can get the wood for free then it's a different argument but I still need to take into account the cost of finding it, cutting it and the space to store and season it.
Should you buy a stove?Whatever the financial arguments, for many people, the cons tend to outweigh the pros of having a wood burning stove.
Written in November 2011