Wood burners
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How wood burners work
A good wood burner heats the room in two ways:
- by convection (warm air) and
- by radiation – this heats objects directly.
Energy efficiency
Modern wood burners produce limited air pollution and average 75 % efficiency.
In comparison the efficiency of open fires can be as low as 10 % and basic wood burners such a pot belly stoves are only 45 % efficient.
In each of these cases you also produce large amounts of air pollution. If you do have an open fire that you don’t use, make sure that you block up the chimney to prevent draughts and heat loss.
It is cheaper to burn firewood in an efficient wood burner than to get the equivalent amount of heat from electric or gas heating. Some people even have access to free firewood.
Wood quality
The quality and condition of the wood are important. It should be well seasoned (dried for at least a year) and stored under cover. Where possible, use wood from plantation forests rather than native types such as Manuka.
Choosing a wood burner
When choosing a wood burner, consider:
- the size of the area you want to heat
- the thermal needs of your house
- the home layout.
Unless your house is very open-plan you need to consider how to get the heat to all the rooms in the house.
Most wood burners generate far too much heat for one room, and you may need a fan and ducting system to get the heat into other rooms.
Installation
A wood burner can be freestanding on a hearth or inserted into a fireplace to replace an open fire. Putting the burner in an existing fireplace can make installing the flu easier, but also means that the room will take a bit longer to both heat up after the burner is lit, and cool down after it goes out, due to the extra heat that the fireplace itself will absorb.
Option of a wet-back system for hot water
If the layout of your house and its hot water system are suitable, wood burners can be equipped with a wetback system to heat household hot water.
This can complement a solar water heating system, to make up for the shortfall in the sun's heat during winter months.
Remember that the heat being used by the wetback is not available to heat the house.
Take this into account when choosing the best size burner for your home.
Emission discharge standards
All wood burners installed on properties less than 2 hectares must have a discharge of less than 1.5 grams of particles for each kilogram of dry wood burnt, and a thermal efficiency of at least 65%.
Take action
Use an authorised woodburner
Check the Ministry for the Environment’s List of authorised woodburners. [Ministry for the Environment website.]
Get building consent approval
Wood burner installation needs a building consent from your local council. Contact your local council to find out more at Local council website directory. [Local Government NZ website.]
Check emission standards
Check the discharge standards for wood burners at National environmental standards: Authorised wood burners. [Ministry for the Environment website.]
More information
- Consumers’ Institute Woodburners free checklist. [Consumers’ Institute website.]
- Rules for domestic fires and wood burners (PDF 229 KB) [Auckland Regional Council publication.]