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Is your wood fuel up to standard?

Posted by Cathy Debenham on 24 July 2009 at 10:03 am

A log's a log isn't it? Well, not if you want it to burn well it isn't. As with all woodfuel, the efficiency with which it burns depends greatly on its moisture content. For logs to burn efficiently in a boiler the moisture should be at or below 25%. That’s not all. They should also be seasoned, and cut to the right size.

So how do you know whether your supplier is offering you logs of a high or low standard when there is no kite mark that you can measure things against? The answer is to plan your supply chain, and become an informed customer according to Stephen Green, biomass project manager at RegenSW.

He suggests that by now you should have next winter’s seasoned log supply already in storage. He also advises you get a wood moisture meter, so that you can check the moisture level both in the wood you buy and that which you’re storing (prices start at around £10 on ebay).

The lack of standards in the log market, which has boomed recently thanks to the rise in energy prices, is because it is dominated by the grey market. Firewood is often sold by the load or half load, which makes it almost impossible to compare prices between suppliers. Ask your supplier for a more specific indicator of volume. It’s also helpful to know what size the logs are cut to and whether they’ve been split, so you know how suitable they are for your appliance. Large and small are a bit too vague.

Moisture content will be affected by whether or not the logs have been seasoned, and if so, for how long. Whether they’ve been stored under cover and how long they since they were split will also have and impact. Freshly cut, green material will have a moisture content of 55%, compared with 20-25% for two-year seasoned wood that has been split.

Buying appropriate pellets and wood chips is not so complicated. Although there isn’t a UK standard in operation, most of the industry has adopted the Austrian Onorm standards. Boilers and stoves will specify which standard of fuel is needed for it to operate effectively.

Moisture content is just as important for the performance of both fuels, so it's worth putting a wood moisture meter on your Christmas present list for them too.

Photo by iangbl

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5 comments - read them below or add one

Between the Green

Between the GreenComment left on: 2 December 2010 at 11:42 am

Hi, Jon. Brilliant, thanks for the clear advice. Apparently the wood is Tanalith E from Arch Chemicals, and I'v emailed them to ask for specific info.

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Jon Edge

Jon Edge from Fair EnergyComment left on: 21 November 2010 at 12:35 pm

Hi Between the Green, there are health and environmental concerns burning treated wood in a biomass boiler and as a rule you shouldn't burn any wood that has glue, varnish, paint or preservative in it. The risk of respiratory illness is possible and depends on the substances involved among other factors, so the safest approach is not to use any treated wood at all, especially if acids are being created in the emissions.

Suppliers of wood fuel and especially pelllet know not to let any treated wood into the fuel supply, so there should be no risk from a reputable and regulated supplier.

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Cathy Debenham

Cathy DebenhamComment left on: 15 November 2010 at 3:46 pm

Hi Between the Green. This is a quote from Jon's latest blog (point number 14), which partially answers your question: "There should never be any wood which has paint, varnish, glue or any other additives as this could produce harmful emissions and damage the boiler. Chip and pellet should be bought at the correct moisture content and without any harmful substances in."

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Between the Green

Between the GreenComment left on: 13 November 2010 at 11:57 am

Since last February, I have been burning offcuts in my biomass boiler. These come from a workshop where they make sheds, fencing and other outdoor stuff, so the wood has been treated with some sort of preservative.

Are there any health risks involved in burning this treated wood? My son has been ill since about the same time and we are wondering if there is a connection.

We also burn pellets. Can we be sure that the sawdust that went into these comes from untreated wood, or is there the same risk as with the offcuts?

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John Smith

John SmithComment left on: 29 July 2009 at 10:00 am

If the wood is too wet then it can be dried. If it is too long then cutting it shorter is very laborious and half the pieces are then too short. My boiler manufacturer, Baxi,  advises against burning too much Oak at once so the wood species also matters.

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