Wood burners

Well operated, modern wood burners are energy efficient, produce low levels of air pollution and use one of NZ’s most renewable forms of energy.

Pros and cons of modern wood burners

  • They can be relatively cheap to run - even if you have to buy firewood.
  • Wood is renewable - and New Zealand has extensive areas of forestry.
  • Wood burners work during power cuts - many free-standing models can be used for cooking as well as heating.
  • Wood burners can be particularly suited to cold climates - but be sure to check the Ministry for the Environment’s list of authorised wood burners (link below), to make sure yours is compliant with the National Environmental Air Quality Standards, and rules that apply in your region.
  • Some wood burners can be equipped with a wetback system to heat water - check with your supplier about this option.
  • The greenhouse gas emissions from burning wood from sustainable forests are small. 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. This means the net greenhouse gas emissions from burning wood from sustainable forests (where new trees are planted after tree felling) are small in comparison to heating with gas, coal or electricity1.

  • New, correctly operated low-emissions wood burners are clean burning and reduce the impact on air quality.

  • Even modern low-emission wood burners can emit harmful air pollution if they are used incorrectly or poorly maintained2. Never burn wet, chemically-treated or painted firewood, or household rubbish.

List of authorised wood burners - Ministry for the Environment website

Learn how to light a smoke-free, efficient fire - Warmer Cheaper website

Find out what to look for in a wood burner and compare models - Consumer website

Wood burner checklist

  • Insulate first - starting with your ceiling and floor. This will make your house easier and cheaper to heat properly.
  • Make sure you have a sheltered space to store and dry your firewood - exposed to some wind but protected from the rain.
  • Get a building consent - from your local council, before you install a wood burner. Check with them to find out if they have any extra requirements for solid fuel burners. If an illegally installed wood burner causes a fire, it may invalidate your insurance cover.
  • Choose a Ministry for the Environment authorised wood burner - burners installed on properties less than 2 hectares in size must meet certain emissions and efficiency standards. Check out the Ministry for the Environment's list of authorised wood burners (link above). Buy the most-efficient wood burner that suits your needs.
  • Free-standing or insert model? - Freestanding wood burners tend to be more efficient and cheaper to install. However, if you want to replace an existing open fire, an insert model can be fitted into the same space and will be much more efficient than the open fire.
  • Work out what size you need for your home - wood burners need to be carefully matched to the room you want to heat. Ask your heating supplier to advise you on the right size heater for your needs.
  • Decide whether you want more radiant or convective heat - wood burners release their heat through a combination of heat radiation (which heats objects) and convection (which heats air). The amount of each varies from model to model.
      • Radiant heat - wood burners that produce mostly radiant heat make the room feel warmer than the air actually is. This makes them particularly suitable for large rooms with high ceilings and for rooms where you have poor insulation and draught issues.
      • Convective heat - convective wood burners heat the air around them, which then rises to the ceiling. This means you get less heat in the bottom part of your room, unless you use a ceiling fan to mix up the hotter and cooler layers of air. Convective heat makes it easier to move some of the warm air to other parts of your home with a heat transfer kit.
  • Wetback models - use the heat of the wood burner to heat water, by circulating water between the wood burner and the hot water cylinder through pipes. The hot water cylinder needs to be placed reasonably close to the burner. A wetback can be cost-effective if you use the wood burner daily for extended periods in winter, and if your household uses a reasonable amount of hot water. Note that some wood burners won’t meet emissions and efficiency standards with a wetback fitted - check with the supplier.
  • Use a certified installer - quality installation is fundamental to your wood burner's performance and safety. We recommend that you have your wood burner installed by a Solid Fuel Appliance Installation Technician certified by the New Zealand Home Heating Association.
  • Install a heat transfer kit - most wood burners generate more heat than you need for one room. Unless your house is open-plan or has internal door openings that go right up to the ceiling, excess heat won’t easily get to other rooms. Heat transfer kits distribute the heat by pumping the warm air into other rooms in your house. You can buy these kits from DIY and electrical stores, but we recommend you contact a professional tradesperson for advice as there are a lot of factors that can affect how well they work.

Local council website directory - LGNZ website

New Zealand Home Heating Association website

Using wood burners wisely

Burning dry, untreated and unpainted wood of the right size and operating the wood burner correctly helps reduce the impact on air quality in parts of NZ that are prone to winter smog.

  • Follow the manufacturer's operation and safety instructions.
  • Use safety guards to protect children and pets.
  • Plan ahead and use well-seasoned, dry firewood - stored under cover in a well-ventilated, windy and sunny place for at least a year to dry out before use.
  • Burn firewood of the right size – less than 110mm diameter.
  • Use the right wood at the right time - lighter wood (often called 'softwood') like pine is good for making kindling and getting a fire started. Once the fire is well established, denser wood (hardwood) will burn for longer and give more heat. If you can, use wood from plantation forests (for example pine and gum) rather than native woods like Manuka.
  • Don’t burn chemically treated wood, salt impregnated wood like driftwood or household rubbish - as it can corrode your wood burner and flue, emit toxic gases and leave toxic residues in the ash and flue.
  • Don’t burn coal in a wood burner, unless the manufacturer specifically says you can - otherwise you can damage your wood burner.
  • Regulate the heat output by adjusting the amount of fuel you load - don’t dampen the air control.
  • Keep the air setting high enough for a clean burn - too much or too little air cools the fire, and produces smoke. Place large pieces of wood on a good bed of embers and set the burner at a high temperature.

Learn how to light a smoke-free, efficient fire - Warmer Cheaper website

Maintaining your wood burner

Maintaining your wood burner regularly is important for safety, performance and longevity. If a poorly maintained wood-burner causes a fire, it may also invalidate your insurance cover. Chimneys and flues need to be cleaned at least at the start of each heating season. Most wood burners and flue systems have parts that you need to replace or clean periodically. Don’t burn coal in a wood burner or you’ll damage it. Ask the manufacturer to recommend someone to inspect and service your wood burner, or contact a member of the New Zealand Home Heating Association.

New Zealand Home Heating Association website

Open fires and older wood burners

Open fires are often inefficient - most of the heat is lost up the chimney. They also create a draught that draws cold air into the house and produce large amounts of air pollution. Older wood burners and pot belly stoves can also be inefficient and produce air pollution unless maintained and refurbished to keep them in good working order.

What to do with unused open fires

If you have an open fire that you don't use, stop draughts by putting some crumpled up newspapers into an old plastic shopping bag to block up the chimney. If you do block the chimney, make it very obvious so nobody tries to light a fire with the chimney blocked.
You can also replace an open fire with a modern enclosed wood burner which will perform much better. Insert models can often be fitted into an open fire space.

 

References

The Ministry for the Environment’s Guidance for voluntary greenhouse gas reporting - 2016: Data and methods for the 2014 calendar year. In addition to the direct carbon dioxide emissions released when burning wood, there are other greenhouse gas emissions from transporting and processing firewood, plus direct methane and nitrous oxide emissions released during wood combustion.

2 Ministry for the Environment’s Health and Air Pollution in New Zealand Study