Wood burners

Why get a modern wood burner?

Modern wood burners are highly energy efficient and produce limited air pollution. They use a form of renewable energy and so are essentially carbon neutral. Many wood burners manufactured after 2005 are likely to meet the current efficiency and air quality requirements. If you have an older wood burner, check with the manufacturer to how efficient it is compared to newer models.

By comparison:

  • Open fires are often very inefficient - most of the heat is lost up the chimney. Open fires may warm the room they occupy a little bit, but create such a draft that they draw cold air into the rest of the house. Open fires also produce large amounts of air pollution
  • Basic wood burners (such a pot belly stoves) are only about 45% energy efficient. Basic wood burners can also produce large amounts of air pollution.

Benefits of modern wood burners

  • It's cheaper to burn firewood in an efficient wood burner than to get the equivalent amount of heat from electric or gas heating
  • The average energy efficiency of modern low emission wood burners is between 65 - 70%
  • Wood is carbon neutral. While trees are growing, they capture carbon dioxide from the air. This carbon dioxide is released either when the wood is burnt, or when the tree dies and rots
  • Wood is renewable and sustainable. New Zealand has extensive areas of forestry. Generation after generation of trees can be sucessfully harvested to produce firewood
  • Some people have access to free firewood, meaning free fuel.

Choosing a wood burner

There are a number of things to consider when choosing a wood burner:

The size of the area you want to heat

Most wood burners perform best near to their maximum output. If you often run your burner at low settings (damped down) it may be too big for your needs. Modern wood burners usually meet the required emissions and efficiency standards by not being able to be damped down much. You need to take this into account if you are replacing an old wood burner.

The heating needs of your house

How well insulated is your home? Does it have thermal mass? Brick or concrete construction has a lot of thermal mass and can hold heat. Houses made of timber have low thermal mass and don't store heat well. The more thermal mass you have, the longer your house will take to warm up, but it will also stay warm for longer after you stop heating it.

The layout of your home

Unless your house is very open-plan, you need to consider how to get the heat to all the rooms. Most wood burners generate much more heat than is needed for one room, and you may want to install a fan and ducting system (heat transfer) to get the heat into other rooms. Kits are available from DIY stores, or can be installed by a tradesperson.

To get an independent idea of how much heat is needed in your room or home, visit the the Consumer website to use Consumers' NZ choosing a heater calculator.

The quality and condition of the wood you burn

It should be dried for at least a year and stored under cover. Where possible, use wood from plantation forests (pine, gum, etc) rather than native types such as manuka.

Choose an authorised woodburner

Check out the Ministry for the Environment's list of authorised woodburners.

Wood burners installed on properties less than 2 hectares in size can only discharge as much as 1.5 grams of particles for each kilogram of wood burnt. They must have a thermal efficiency of at least 65%.

Installation of your wood burner

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 it also means that the room will take longer to heat up after lighting the burner. It will also take longer to cool down after it goes out. This is due to the extra heat that the fireplace absorbs.

Get building consent approval

Wood burner installation needs a building consent from your local council. Contact your local council to find out more about consents at Local council website directory.

Option of a wet-back system for hot water

Some wood burners can be equipped with a wetback system to heat household hot water. This is as long as the layout of the house and its hot water system are suitable for this purpose.

Such an installation can complement a solar water heating system, making up the shortfall in the sun's heat during winter months.

Remember that the heat being used by the wetback isn't available to heat the house. Take this into account when choosing the best size burner for your home.

What to do with your old open fire

If you have an open fire that you don't use, make sure that you block up the chimney. This will prevent heated air escaping from your home.

Older wood burners

If you have an old wood burner, it is worth getting it inspected and serviced. Many wood burners have parts that are designed to be wear out and be replaced periodically and it isn't uncommon to find wood burners that have been partially melted inside from people burning coal in them.

Check with the manufacturer of your wood burner to see who they suggest for inspections and servicing. Otherwise contact someone in your area who sells and installs woodburners, they should be able to help you.

More information

From the Resource Centre

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