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How to choose logs for a wood burning stove

Posted by Cathy Debenham on 31 March 2011 at 10:12 am

Moisture content and the density of the wood are the two main things to bear in mind when choosing logs for a wood burning stove. Not only will they affect the amount of heat you get per kilo of fuel, but they will also make a difference to how well the wood burns - whether you get nice flames or tar and smoke.

Moisture content has the most effect. For the wood to burn, any water in it must evaporate. This evaporation process - ie steam going up the chimney - means that less of the energy released will be used as useful heat.

If your logs aren't dry, then the fire will smoulder and create tar and smoke. This in turn can damage the lining of the chimney (or gunk it up), and blacken the glass of the the stove.

So, to maximise the heat you get from the wood, either buy it well seasoned, or make sure that you dry it yourself before burning. Cracks in the wood, and bark that comes off easily, are both ways of telling if it is well-seasoned. Also you can tell by the weight of the log, or by using a moisture meter.

Fresh green logs with a moisture content of around 60% will provide 2,000 kWh of heat per tonne. Air dry logs with moisture content of c.25% will provide twice as much heat.

The other key issue is the density of the wood. Hardwood (which comes from deciduous, broadleaf trees, such as oak or ash) tends to be heavier than softwood (mainly conifers). This means a tonne of hardwood will need less storage space than a tonne of softwood. Hardwood also burns for longer than softwood, so you won't have to top up the stove so often.

However, softwoods are cheaper to buy, and easier to light.

This article is based on information provided by the Biomass Energy Centre

Photo by Scott Campbell

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Comments

1 comments - read them below or add one

Certainly Wood

Certainly WoodComment left on: 1 April 2011 at 9:09 am

I agree with all Cathy's comments. Over 80% of stove problems are caused by wet wood so it is a national problem, particularly when you buy wood from garage forecourts. Here the wood is not only so wet, but also invariably softwood if bought from the supermarket garage forecourts.

Hetas have recently launched a new quality assurance sheme called the Solid Biomass Assurance Scheme and this is the 1st of its kind in the UK. Certainly Wood was the 1st to become approved under this new scheme. It has helped our business focus even more on our quality, which we are able to keep consistenly high due to the use of our wood fired kilns.

Seasoning wood naturally is brilliant if you have the space to do it, bearing in mind a single stove is likley to require approx 3-4 m3 of logs per season. Therefore if you are going to dry your own over 2 years you need to have cut and stored approx 8m3 of logs at any one time. Thats a lot of space.

This is where kiln dried comes into its own and whilst slightly more expensive it does give customers the luxury of being able to buy in small quantities logs that are "oven ready" and with the piece of mind they will perform everytime - Clean burn with maximum heat output which is key as Cathy says.

Verys sensible to arm yourself with a moisture meter too to check on the quality that you are buying. All too often log supplies say it has been seasoned for 2 years but often it is still green. For more info on all this have a look here:  www.certainlywood.co.uk

 

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