Appliances
Woodburners
Introduction
With winter biting a woodburner may appeal. Our database includes nearly 70 models, including wetbacks and inserts.
This report explains how woodburners work, the emission rules, and what to look for when buying a woodburner. And our database of 69 freestanders, inserts and wetbacks sorts out the cleanest and most efficient models.
This report does not contain heat output data. Currently no one organisation within New Zealand holds a complete list of output figures; they have to be obtained from each individual manufacturer. We are currently in the process of negotiating with the Home Heating Association to collect this information.
Models in our database
All woodburners in our database comply with the Ministry for the Environment emission rules.
Pros and cons
Nothing's nicer than toasting yourself in front of a cosy fire. Using a woodburner to heat your home means you're not captive to energy companies and their ever-rising prices - and you can still be warm if there's a power cut.
Burning wood is carbon-neutral because it's a renewable resource, but burning it cleanly is the key to making it enviro-friendly.
Apart from solar heating, all winter-heating options carry an environmental cost. The Ministry for the Environment estimates that about 30 towns and cities regularly exceed the standard for ultra-fine-particle air pollution.
Smoke particles are measured in microns: one thousand microns equals a millimetre. It's the fine (10 microns or less) particles in smoke that, when inhaled, can lodge in the lungs and cause respiratory diseases.
That's the reason you should burn the right-sized dry wood in a modern efficient woodburner.
Woodburners are really cheap to run if you can scrounge the right firewood and they're still cheap even if you buy it. Of course, there's some extra hassle in sourcing, (possibly) chopping, and storing firewood - and in having to do this many months before winter strikes. You also have to light the fire when you want heat ... and refuel it ... and empty the ashes. But it's you - and not the power company - who's in charge of the heating.
Emission rules
Cold winter air laden with smoke particles is no joke - it's a health issue for us all, but especially for Canterbury, Nelson, and Otago residents, where winter air pollution is worse than in other places.
On 1 September 2005, the Ministry for the Environment tightened the emission rules for new woodburners for all urban areas.
Before, the smoke had to consist of no more than four grams of particulate (smoke particles) per kilogram of dry wood burnt. Under the new rules, the limit for woodburners installed after 1 September 2005 is only 1.5g, and the burners must be at least 65 percent efficient.
Because of their pollution problems, in Canterbury and Nelson the authorities have gone further. Canterbury has lower emission-limits than what the National Environmental Standard (NES) requires and they both carry out physical checks on woodburners, to make sure production-line models' critical dimensions are the same as those of "sample" models submitted for testing. (See "Compliance testing" below.)
One upshot of this is that the Canterbury and Nelson local authorities discovered that some woodburner models in stores had design changes and weren't the same as the sample that had been submitted to the lab for testing.
And, as we reported in our 2007 news item, the Ministry for the Environment also did some checking. This led to a number of models being removed from the ministry's online list of authorised woodburners (which is limited to models that meet the Canterbury and Nelson requirements). It also prompted the ministry to investigate further.
Not good enough!
In its 2008 investigations, the ministry randomly selected 10 woodburners and bought them anonymously. It then checked their efficiency and emissions, and whether they were true to their design.
The results were disturbing. Of the 10 burners, only 2 passed all the tests. Of the remaining eight, one was borderline in its efficiency and seven failed. Two failed because of a minor problem, three because of a moderate problem. One had a serious problem, and another a very serious problem.
These are major shortcomings. Some woodburner manufacturers should be blushing.
What's more, it's probable that non-compliant woodburners have been installed in urban homes since 2005.
Check your local air quality
Regional councils monitor air quality every day and most put the data on their websites. The following cities and towns have monitoring data live on their regional council website:
Tauranga, Rotorua, Whakatane, Te Kuiti, Tokoroa, Taupo, Hamilton, Putaruru, Reefton, Rangiora, Kaiapoi, Christchurch, Ashburton, Timaru, Waimate, Geraldine, Alexandra, Clyde, Cromwell, Arrowtown, Ranfurly, Central Dunedin, Mosgiel, Milton, Invercargill, and Gore.
Compliance testing
All new woodburners must be tested for compliance with the National Environmental Standards (NES) - and this must be done by an approved laboratory. The manufacturer sends a sample model to the lab, which notes the critical dimensions of the model and tests its burner's efficiency and emissions.
If a model passes the tests, it's NES compliant. The manufacturer then labels all production of that model as such.
Wetbacks
There seems to be some confusion about the efficiency requirements of woodburners that have wetbacks.
Woodburners for urban areas have to comply with National Environmental Standards (NES), which means they must have a minimum "space-heating efficiency" of 65 percent. (See Emission rules for more about the National Environmental Standards for woodburners.)
"Space-heating efficiency" is the efficiency of converting the wood's heat energy into space (air) heat. The water heating from the wetback isn't included in the efficiency calculation - so when some of the wood's energy is going into water heating it means that relatively less is going into space heating.
This means not all woodburner models can be fitted with a wetback in urban areas - but some can.
Wetbacks are expensive to install and require the hot water cylinder to be placed reasonably close to the burner. The payback period for a wetback depends on how you use your woodburner. If the woodburner is not used every day, a wetback is unlikely to be cost effective.
Checklist
If you're about to buy a woodburner, here's what to consider.
Type
Freestanding models are generally the most efficient (for a given firewood load, they return the most heat to a room). They're also the cheapest to install. But if you have an existing open fireplace, an insert model is most often the way to go. Although insert models are not as efficient as freestanders, they're way better than an open fire.
Heat output
Choose a woodburner with a heat output suitable for your home. If you have a non-draughty well-insulated home in the north of the North Island then 10kW should be plenty. A larger house - or the same-sized but less-well-insulated and draughty house - further south will require more heat output. Think in terms of 12-14kW.
In non-open-plan houses there's no point in overheating the lounge while the rest of the house stays cold. Install a heat-distribution system to help spread the heat throughout the house.
Be careful about manufacturers' heat-output claims - some grossly exaggerate what you'll get. Always check the compliance plate (pictured). This has to be on every woodburner that's sold - and it states the tested heat output, along with the efficiency and emissions rate.
Radiant/convector
Radiant burners beam heat directly to objects in the room, and are best for less well-insulated houses with high ceilings. Convectors heat the air then circulate it into the room, and are best for well-insulated, non-draughty houses with low ceilings. All woodburners work in both modes to an extent, but most are designed to be predominantly one or the other.
Controls/cleaning
The controls should operate smoothly, and it should be relatively easy to clean the outer surfaces and empty the firebox.
Flue system
The flue must have a larger diameter outer shield around it where it passes through the ceiling and attic space. Some of the newer designs have this air-gap vented outside rather than into the room (outside venting stops hot air escaping from the room). Some other woodburners get the air needed to burn the wood from outside the house rather than from within the room: this improves efficiency and reduces drafts.
Emissions
The lower the particulate emissions from your fire, the less of a health hazard you'll be causing. You can find this out from the woodburner's compliance plate. See Emission rules for more information about emissions.
Wetbacks
A wetback uses copper pipes to circulate water from the woodburner to the hot-water cylinder and back. They're expensive to install and the hot water cylinder needs to be placed reasonably close to the burner. The payback period for a wetback depends on how you use your woodburner: if the woodburner's not used every day, a wetback is unlikely to be cost effective. See our section on wetbacks for more information about this type of woodburner.
Safety guards
Woodburner surfaces can get very hot and can be a danger to small children. Protective guards are available, and highly recommended.
Building consent
Before you buy a woodburner, make sure your local authority will allow you to install the model you want: some councils will only allow installation of models from their recommended list. You will also need to get a building consent before you install your woodburner (you're unlikely to get one retrospectively). If an illegally installed wood-burner causes a fire, it may invalidate your insurance cover.
Installation
A poor installation job can ruin the heating and emissions performance of the best of woodburners. Check that your installer has New Zealand Home Heating Association certification or is otherwise suitably experienced.
How woodburners work
It's a two-stage process. First, if the wood is hot enough, the combustible creosotes and resins will evaporate out of the timber and will be burnt as gases (if these gases are not burnt completely the result is smoke).
The evaporation of the gases turns the wood to charcoal, which then burns easily and cleanly - and produces most of the heat.
To burn as cleanly as possible, the fire needs to be as hot as possible. It also needs the right amount of air to support the combustion. Too much air cools the fire and smoke is produced. Not enough air has the same effect.
Modern woodburners burn efficiently because the firebox is lined with firebrick material, making a hotter fire. The combustion air is carefully admitted to give the most complete combustion possible. The resulting efficiency (conversion of the fuel energy into heat in the room) is around 65 percent.
Contrast this to the traditional open fire, which admits far too much air, cooling the fire and giving an efficiency of 15 to 20 percent. Some even have negative efficiency - they draw cool air into the house, warm it and send it up the chimney!
What to buy
The following models of freestanding, insert and wetback woodburners are worth considering. For more information on the performance of all models, see the Woodburners database.
Freestanding models
- Atlanta Bay
- Bronte AG (top outlet)
- Ethos Genesis
- Ethos Phoenix
- Kent Quantum Max Clean Air
- Masport LE 2000 Series 2
- Metro Eco Euro Ped (with direct vent)
- Metro Eco Euro Rad
- Metro Eco Euro Trad (with direct vent)
- Metro Eco Tiny Rad
- Metro Eco Tiny Trad
- Milan Caldo C/A Harmony Series
- Osburn 1600
- Pyroclassic IV
- Quadra Fire 2100 Millennium ACC
- Quadra Fire 4300 Millennium ACC
- Warmington Lewis
- Woodsman Matai ECR 165
- Woodsman Pelorus - 165
Wetback models
- Ethos Aquos FS100W with wetback
- Lady Kitchener AG Clean Air with wetback
- Osburn 1600 with wetback
- Pyroclassic IV with wetback
Insert models
- Athena Bay AG
- Ethos Ares (with flue shield)
- Forte Bay AG
- Masport LE 4000 Provincial
Our advice
- Don't buy a woodburner without making sure it complies with the emission rules and that your local council will allow it to be installed.
- Make sure you get a building consent before you install your woodburner.
- Insulate your home as much as possible. Better-insulated homes require less heating.
- If your home isn't open plan, install a heat-distribution system.
- Buy the cleanest-burning woodburner that suits your needs.
- Burn only dry seasoned wood - and make sure it's less than 11cm in diameter.
More information
- Ministry for the Environment's list of authorisied woodburners: www.mfe.govt.nz
More from consumer.org.nz
Report by Bill Whitley.