Woodburners test results
Compare heat output, emissions, specifications and more in our database of over 150 models.
Home, heating & renovation
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Choosing the right woodburner depends on your house and whether you want a wetback. Getting the best performance depends on the size and type of wood you burn. We explain what to look for and compare over 150 models in our product database.
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Choosing the right woodburner depends on your house and whether you want a wetback. Getting the best performance depends on the size and type of wood you burn. We explain what to look for and compare over 150 models in our product database. Join Consumer and use our expert test results and recommendations to find the model that's right for you.
The large amount of radiant heat produced by woodburners suits many of our houses – especially older, poorly insulated and draughty homes with high ceilings. A properly sized and installed woodburner can heat the whole home.
Many people also like the toasty radiant heat a woodburner produces. Some models can heat hot water and all of them can be used during a power cut. Many have a flat top surface for heating a kettle – or even for emergency cooking.
Burning wood is carbon-neutral because it's a renewable resource, but burning it cleanly is the key to making it enviro-friendly.
The NES sets standards for emissions and efficiency. The emissions figure is the number of grams of smoke particles for every kilogram of dry wood burnt. The NES requires that this be less than 1.5g/kg. If you live in Canterbury or Nelson the rules are even tougher.
The efficiency figure is the percentage of the theoretical maximum heat contained in the firewood that the burner delivers to the room. The NES requires this to be 65 percent or greater for woodburners in urban areas.
All new woodburners must be tested for compliance with the 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.
However, several tests – including our own – have shown the emissions figures obtained in the lab can be exceeded many times over when the woodburner is installed in a house and is burning real firewood.
That means NES-compliant woodburners are still probably significant polluters. It also means regional authorities may have poor information when trying to assess the pollution impact of the woodburners installed in an “airshed” in their area.
This means, for instance, a burner that automatically adjusts its airflow to minimise emissions during the burn cycle cannot be allowed. Additionally, the test doesn’t include the start-up period – when there’s often the most pollution.
Once the testing is completed, the internal design of the burner isn’t allowed to be changed. So it’s illegal to retro-fit any device to the burner, or its flue, that might improve performance.
The upshot is that the NES test which was meant to improve the cleanliness of woodburners has stifled design innovation. We’re aware of several technological developments that have been “caught” by the rules and so haven’t been implemented.
A new standard called the Canterbury Method (CM1), sponsored by Environment Canterbury (ECAN), could be the solution. This CM1 standard won’t replace NES – but because it requires better emissions and efficiency performance than existing standards local authorities will be able to choose to use it.
The new method has been developed in response to the needs of people rebuilding houses after the Christchurch earthquakes. It allows CM1-approved woodburners to be installed in some areas where woodburners had been banned for new houses.
The new method takes a different approach from the NES: it specifies the desired emissions and efficiency but not how to achieve them. It also tries to mirror how people actually use their woodburner. So it has a full-burn test cycle that measures a woodburner’s performance through light-up, warm-up, burn, refuel and die-down.
We know of two woodburners that can pass this test:
Both of these burners have received resource consent to be installed in Canterbury properties where a wood fire could not previously be used.
We look forward to more innovative and clean burning products being developed under this new standard.
This means it's trickier to state a definitive heat output for woodburners than for other types of heater, because different testing methods will give different heat outputs – even for the same woodburner.
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Firewood must be seasoned (less than 25 percent moisture content) and must also be the right size (fits through a 110mm hole) to burn with maximum efficiency and minimum pollution. That means buying firewood several months (hardwood dries more slowly than softwood) ahead of winter and storing it (where air can circulate but it’s sheltered from the weather) … or paying more for dry firewood.
Calculate the right size woodburner for the area you want to heat. Measure the floor and ceiling areas in square meters (length times width in metres). Usually the ceiling area is the same as the floor. Measure the wall and window areas in square meters (height times width in metres). Enter the areas you have measured into the calculator below.
"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.
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Pellet burners have some real advantages – if you can source pellets at a reasonable price.
Most pellet burners look like a conventional woodburner and are available either as a free-standing model or an insert into a fireplace. You can even get a basement-furnace model for central heating.
But pellet burners burn only compressed wood pellets, which you buy in 15kg or 20kg plastic bags or in bulk. The pellets are loaded into a hopper at the back of the unit and are fed into the fire through an automatic feed system.
Adjusting the rate the pellets are consumed gives you control over the amount of heat produced.
Compared to sources like firewood, there are a limited number of wood pellet suppliers in New Zealand. Check there is a manufacturer near you before investing in a wood pellet burner. If you have access to cheap firewood it’s probably best to go with a log burner.
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