Even as we begin a new millennium, with our astounding rate of technological innovation, we still love the homely flicker of a wood fire to keep us warm. We share this with countless generations before us. As with most things the wood fire has its advantages and disadvantages. Some of these are canvassed below.
The Benefits of wood fuelled heaters:
- Wood heaters are capable of providing very high heat outputs. Most wood heaters on the market today, if run at their maximum burn rate and regularly refuelled, will produce heat outputs of 20 to 30kW. By comparison, a typical oil heater has a maximum heat output of 7 or 8kW. The very high heat output of the wood heater means that rooms can be heated quickly and the heat can be circulated through the whole house, thus achieving comfort levels only otherwise possible with central heating.
- Alternatively, many wood heater models are capable of burning one load of firewood for 10 hours or more without the need for refuelling. This means heaters do not have to be re-lit in the morning or when coming home from work. It also means the living space remains warm the whole time.
- Wood heaters can be very cheap to run. For example, firewood costing $300 per tonne means the energy cost is about 2.55 cents/MJ (mega joules). By comparison, petrol at $1.20/L works out at 4.5 c/MJ, or electricity at 33c/kWh is 12.85 c/MJ (ie for radient heat not heat pump). If the same appliance heats water, the cost efficiency of wood is enhanced significantly.
Firewood and wood-fires are simple and easy to use and maintain. Firewood is safe and simple to store compared to oil or gas. This means an entire winter’s fuel supply can be acquired well in advance, providing the assurance that blackouts or strikes will not mean cold winter’s nights. There is a sense of control associated with firewood that more industrial, corporatised fuels lack.
- There are some very important environmental benefits associated with plantation grown firewood .
- The amount of carbon dioxide emitted when wood is burnt is the same as that removed from the atmosphere when the tree was growing. However, approximately half the biomass of the tree remains under the ground as sequestered carbon.
- A sustainable firewood industry based on plantation grown wood provides habitat for wildlife and helps prevent problems like soil erosion and salinity.
- There are also broader economic advantages in supporting a firewood industry composed of small, labour intensive local businesses, which currently generate around $100 million per year in rural wages, or ½ million days of work (roughly equivalent to 2000 full-time jobs).
- The wood heater industry also provides direct and indirect benefits. Present wood heater sales are estimated at about 20,000 units per year, worth about $30 million and supporting around 1000 full-time equivalent positions (manufacture, retail, installation and maintenance).*
Problems associated with wood heaters:
There are two potential downsides to using wood as a fuel:
Taking 4 to 5 million tonnes of firewood per year (Australia’s estimated harvest) out of our woodlands and forests is having serious ecological impact. Activities such as the removal of fallen timber, dead branches, live trees and hollow logs (from the ground, or standing dead trees) are removing habitat for many species. . It is estimated that 303 native species in Australia use hollow logs.
Other impacts on biodiversity of wood collection include the spread of weeds and diseases like Phytophthora.
It is possible that Australia could sustain a significant firewood industry without ecological damage, but only if a strong regulatory framework is constructed to ensure firewood comes from plantations, logging residues or other sustainable sources.
Such regimes should have been in place 25 years ago, so that the 5 million tonnes per year of firewood now collected could be met in a sustainable fashion. However, the industry is attempting to make up for this lost time and invites firewood consumers to be discerning in the purchase and use of their firewood.
Wood fires create emissions. These emissions, especially particulates, may create health problems in the community. The extent of such problems depends upon many factors, such as the size and density of the urban area, the local climate and topography, the type of wood heaters used, whether seasoned wood is being burned, and how people operate their heaters.
However, if the wood merchants, heater industry and consumers are well informed and responsible, these problems can be solved or effectively managed.
It is of the utmost importance that consumers ensure that their heaters meet current design standards, that they are professionally installed and that they burn only seasoned, dry wood.
It is worth noting that dense, old growth wood, if burnt in an efficient heater, yields no more heat per unit of weight than less dense, fast grown plantation wood. Dense wood just burns more slowly and potentially produces more smoke. An exception to this is pine, which burns marginally hotter than hardwoods because it contains flammable resins. (Care should be taken to ensure that only an appropriately designed heater is used if a significant quantity of pine is to be used as fuel, otherwise potentially flammable deposits may accumulate in the flue).
*Please note these numbers are some years old.