Get the best out of your firewood
THE most important thing any homeowner can do to ensure their woodburner is operating efficiently is to use the correct wood.
John Swarbrick, technical manager for Aber Holdings, which manufactures Kent home heating products, said all types of seasoned natural softwood may be used in a woodburner but chemically treated wood or salt-impregnated wood such as driftwood should not be used at all.
‘‘These may corrode the components of the burner and flue system. These materials may also emit toxic gases when burnt and will leave toxic residues in the ash and flue.’’
And fossil fuels such as coal are not suitable, he said.
‘‘Do not burn garbage or large quantities of paper, cardboard or similar materials.’’
Swarbrick said the moisture content of the wood greatly affects woodburner performance.
‘‘Well-dried wood is the best thing you can give your burner. This should be seasoned for at least nine to 15 months to lower the moisture content to less than 25 per cent.’’
Softwoods and hardwoods burn well. Most hardwoods are denser than softwoods and will burn longer, hence hardwood is often used to maintain an overnight burn. He warns that poorly seasoned wood means more work.
‘‘You will be carrying heavier loads, getting less output per load and your glass door is more likely to get covered in creosote. A wet piece of wood placed in a hot fire will burn but will spit and splutter, even causing water and creosote to be splattered on the glass and, likely, lead to a flue being restricted over time.’’
The best way to see if a burner is working properly is by the appearance of the flames from the amount of wood it uses, he said.
‘‘Wood is stored energy. If you want a large amount of heat to be produced by your fire, you should use a large amount of wood. If you want less energy, use less wood. Make sure there is enough air flow, so do not overfill a firebox.’’
In normal operation, do not attempt to regulate the output of the burner by using the air control but rather by adjusting the amount of fuel, he said. He advises on cold days when a large heat output is needed, the firebox should be fully loaded after establishing the fire. When the heat has reached a comfortable level put smaller amounts of wood on the fire to maintain it.
‘‘Optimum efficiency will be achieved when you add only the amount of wood needed until the next time you are free to refuel.’’
Many fires will even burn one log at a time once the burner has heated up and a good ember bed exists.
On warmer days, just burn less wood. Make sure the air setting is kept high enough for a clean burn and the room is also adequately ventilated.
‘‘The cleanest burns will occur when large pieces of wood are placed on a good bed of glowing coals and the burner itself is at a high temperature.’’
To promote good air flow around the pieces, he advises using wood of different sizes and shapes. It is possible to load up to two-thirds the height of the firebox chamber but avoid over-firing.
‘‘If the top of the firebox is glowing, you are over-firing. This will damage the burner.
‘‘Store your ready-to-use firewood well away from the burner while it is in use.’’
To get the best possible heating value out of wood, it needs to be seasoned properly. This is best accomplished by planning ahead, as wood can take up to two years to dry out fully.
‘‘A fresh-cut tree can be up to 50 per cent water, which means half of the weight of the log you are carrying is of no use to you.’’
He said that after 12 months of seasoning, the moisture content may have dropped to between 10 and 20 per cent, which will be about as low as it can go without artificial drying.
The shorter the piece of wood and the greater the surface area exposed to the air, the faster it will dry. A good way to prepare your wood is to cut it to firebox-sized lengths and split any pieces over 150mm diameter as soon as the tree is felled.
The siting of a wood pile will greatly assist or hinder the drying process, Swarbrick said. While it should be adjacent to the house or wood storage area, the area should be free of long grass and away from water to provide good circulation of dry air. Place the piles so wind will blow between the pieces of wood and leave 600-1200mm between the faces of parallel wood piles.
It is also advisable to have wood stacked in full sunlight to take advantage of the sun’s drying rays.
Swarbrick said a two- or threesided wood shed is the most convenient place to store wood but if it has to be stored outside over winter, cover the top but not the sides. Allow 300mm overhang on the roof or cover to minimise rain entry.
In a endorsement of modern solidfuel heaters, he said EECA, the Government’s energy efficiency agency, has voiced support for burning clean, dry wood.
‘‘It is regarded as a sustainable resource that is plentiful in New Zealand.’’