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Since the beginning of time, wood has cooked man’s food, preserved his food, fired his pots, and made weapons and implements his for survival, but perhaps its most common use, even today, is to keep him warm.
It would be easy to assume, therefore, that burning wood has become second nature.
But that’s not the case, according to Luke Marinovich, one of the country’s largest wood and heated suppliers who says wood burning is a learned and practised art.
‘How often have you seen a stick of Manuka in a fireplace bubbling at the ends? Or wondered why there’s not as much heat in the wood you are using now as there was in the last lot you used?
‘People come to us for answers to questions like these all the time.’
Acoording Marinovich, a number of things should be considered when using wood for heating, and he offers the following advice.
He says users should understand the types of fuel wood which is available, its advantages and limitations, then recognize the various types of heating systems in order to select the best fuel for that application. Finally it was essential to know how to light a good fire.
Seasoned fuel is important – Fuel wood ranges from soft woods like pine to hardwoods like Manuka. But whatever wood is chosen, the key to a successful fire is to ensure the fuel is as ‘dry’, or as ‘seasoned’, as possible.
Marinovich says that while surface water doesn’t really matter, because that will evaporate quickly, it is important to reduce the SAP levels within the cell structure of the wood itself, and that takes some time.
Softwoods will season quite quickly, in about 6 to 8 months, but it can take up to 18 months for Manuka to dry to an acceptable level.
Gathering and stacking wood in the open air over the summer period is advantageous, because the warmth of the sun and the breeze will automatically evaporate some of the SAP. When the wood gets wet from seasonal rain, the rain water replaces more SAP. Because water is more quickly evaporated, the fuel dries faster.
‘Most reputable wood merchants will build their stocks of wood over the summer months in order to offer partially seasoned fuel, but it is generally not economic to hold stock for the full seasoning period.
Users should purchase wood well enough in advance to allow for the extra seasoning it is likely to need.
Choose a suitable fuel – It doesn’t really matter what fuel wood is used, because all wood has about the same heat capacity per kilogram, whether it’s a soft wood like pine, or a hard wood, like Manuka. The same volume of Manuka will give more heat than an equivalent volume of soft wood, with less refuelling.
Manuka is a good all round fuel, but it must be properly seasoned for peak efficiency, and burnt on an established fire.
A recent development is a fuel made from a selection of mixed woods – a sort of a fuel cocktail – generally gum, macrocarpa and pine.
‘This excellent fuel is somewhat cheaper than Manuka and burns longer than straight softwood.’ said Marinovich.
Softwoods are perhaps the most common fuelwoods available and while they burn well, the heating appliance or fire will need more regular refuelling. One disadvantage of macrocarpa, which is classified as a softwood, is that it tends to spark more than other fuels.
Another fuel option is compressed Samdust ‘Logs’ which burn well in all appliances.
‘These are naturally dried during the production process. ‘They also come in easy to handle boxes, but these logs must be kept dry to prevent absorption of water and subsequent disintegration, but they burn.’
‘Marinovich strongly cautioned against using treated timber of any kind, because the chemicals could pose a health hazard, and be corrosive, even to brickwork.
He suggested careful examination of wood for a green or pink tinge, or markings to indicate chemical treatment. Old painted timber could also pose a threat if it has been painted with lead based paint.
While dry salt borne drift wood could be used in an open fire, its use in any other type of heating appliances should be avoided because it will cause corrosion of the heated or its flue system.
He warned users to look carefully at bagged fuel offered by small operators, because the wood was often packed as soon as it was cut and will never season properly because the packing will prevent the air circulation required for drying.
‘The established outlets ensure that the fuel is air dried for a considerable time before packing’
Radial cracking at the end of logs is a good indication of dryness, as is a ‘ring’ when two pieces of wood are knocked together. A dull thud indicates excessive moisture is present.
Good kindling is necessary to build a good fire. The best is dry, thin pieces of a soft wood like pine, or dry pine cones. Cones however are not recommended as a primary fuel, as they burn quickly, and will need constant replenishing.
Professional suppliers generally sell bulk wood by cubic measurement, and have special hoppers designed to measure the quantity.
‘Selling by weight can be misleading, because weight of wood will depend on its moisture content’
Users who don’t have the ability to store large amounts of fuel can purchase by the bag, but because of the extra labour involved, there is a price premium of about 15%.
It’s important to understand the capabilities and limitations of your heating appliance before selecting a fuel.
Open fires generally have a maximum efficiency of 12%, which means most of the heat generated is carried up the chimney.
Because a fireplace relies heavily on radiant heat for its effectiveness, a mix of coal or carbonettes and hardwood is best. Annual fuel usage in an open fire will be considerably higher than other appliance options.
A pot belly stove is a little more efficient, but the design of the combustion system and gaps around the joints can lead to high fuel consumption.
These appliances provide radiant heat, and it can be difficult to maintain an all night burn because of the amount of fuel they require.
Because the fuel opening in a pot belly is small, many suppliers now produce specially cut fuel for these stoves’.
Best economy will be gained from a modern high efficiency double burning heated which offers both convected and radiant heat.
These appliances have an efficiency approaching 70%, and have the flexibility to safely heat a room or a whole house for weeks on end.
Where ever practical, it makes sense to replace an open fireplace or pot belly with one of these.’
A consumer could expect an annual usage of 2-3 cubic metres of hardwood for whole house heating with a high efficiency heated. Other options will use considerably more fuel, and require more attention, yet not provide the safety or total comfort expected from a high efficiency appliance.
The key to any successful fire lay in the initial lighting.
‘It’s important to have a good base to work from.
* – Set small pieces of dry kindling or pine cones over loosely crumpled newspaper balls or several firestarters, on the grate or on the base of the fire. Light, and wait until the fire is established.
– Place a few medium pieces of dry wood on the burning kindling.
– When these pieces are burning brightly, place the larger pieces on top.
In an open fireplace, this procedure can take some time, while in a high efficiency heated, effective heat will be produced in about twenty minutes.
So what about ash disposal? With the exception of a high efficiency heated, which needs cleaning only every 6 weeks, ashes should be removed each day.
Providing that only untreated wood has been burnt, ash can safely be dug into the garden as it makes an excellent addition to the soil.
Ash which results from burning coal, or coal based fuels, treated, or lead-based painted timber should never be put into the garden, and needs careful disposal. Make sure the ash is cold before removing it from the heating source.
‘Simply looking at the stacks of fuel in a yard is a good indication of its condition.
When you get it home, stack it loosely in a dry, draughty place for as long as possible before usage.
To dry that little bit longer, and useful heat won’t be wasted driving off extra moisture.