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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%.
Contrast this to the traditional open fire, which admits far too much air, cooling the fire and giving an efficiency of 15-20%. Some even have negative efficiency – they draw cool air into the house, warm it and send it up the chimney!
It can feel daunting when you first look at our database. Use these tips to narrow down your choices and hone in on your ideal model.
If you live on a property smaller than 2 hectares then you need to install a woodburner that meets National Environmental Standards (NES). Models that meet these standards are also known as clean air or urban models. Most woodburners in our database are NES-compliant, meaning they have emissions of 1.5g/kg or lower and an efficiency of at least 65%. However, depending on where you live, NES compliance might not be enough. If you live in some parts the Bay of Plenty, Hawke’s Bay, Nelson, Canterbury or Central Otago then the rules about emissions can be much stricter.
(ULEBs) are a new technology designed for installation in areas where older burners are outlawed. These burners meet stringent standards and are able to be installed in clean-air zones where all other fires are prohibited. They’re also highly efficient.
Only allowed on sections larger than two hectares are also available. They generally offer better overnight-burn capability than urban models, ideal for farmers keen for their fire to still be blasting when they wake up early in the morning. The trade-off is higher emissions and lower efficiency.
Working out the heating capacity (kW) required for your home is critical. Woodburners lack the fine control of a heat pump – too small and it won’t be able to keep your home at a healthy temperature, too large and you risk turning your home into an uninhabitable oven. As a rough guide, models under 10kW are best suited for smaller, well-insulated spaces, while large and/or poorly insulated spaces need more than 10kW. For a more accurate gauge on the ideal output for the area you want to heat, use our calculator.
If you have an existing open fireplace you can opt for an insert woodburner that fits inside the old fire cavity. Freestanding models are the best option for newer households, and can now be placed closer to walls with smaller clearances than older freestanders.
Radiant fires offer an intense, toasty heating effect, ideal if you’ve got high ceilings or poor insulation. Convector fires produce a softer, ambient heat through a cyclic convection effect. They heat more evenly but are better for homes with good insulation and low ceilings. Many models are “radiant and convection”, combining both heating modes.
Models with high efficiency give more bang for your buck, extracting more useful heat from each log. Choosing a model with low emissions means less risk of your chimney producing smoke that causes respiratory issues and stinks up your street. Our emissions and efficiency scores give an indication of the relative performance of each woodburner – a score above 7.0 indicates above-average performance.
Woodburners range in price from $1000 to more than $5000. You should also factor in the cost of installation and building consents (usually several hundred dollars more). While ULEBs are the most expensive burners, their greater efficiency means you’ll spend less on firewood.
Finally, consider how the woodburner looks. Some have much bigger windows than others, which can enhance your living area’s ambience, while others have a variety of coloured panels. Some ultra-low emission burners even have a USB charging port. Insert woodburners have varying fascia mimicking the detailing of old fireplaces.
Many people like the toasty radiant heat a woodburner produces. The flip side of woodburners is their contribution to air pollution and their relative lack of convenience.
Woodburner design is an important part of achieving low emissions – but so is the wood itself. We’ve compared prices for pine, macrocarpa and hotmix and explain what to consider when you buy.
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.
This means that some woodburners are compliant without a wetback but not compliant when fitted with one. This is because the heat removed by the wetback reduces the woodburner’s efficiency to below 65%.
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.
One problem with woodburners is they can over-heat the lounge while the rest of the house remains cold. This isn’t healthy. The most common commercially available heat transfer systems use ducting to move warm air. We think the rule on wetback “efficiency” is holding back development of woodburner systems that could distribute heat around the house using a wetback and water radiators.
Tip: If your house is not open plan, think seriously about installing a heat-transfer system.
Pellet burners have some real advantages – if you can source pellets at a reasonable price. Find out what to look for and compare models.
Ethanol burners are popular in Europe as a chic eco-friendly alternative to the hassle of a conventional fireplace. Are they a good option for your home?
Consumer Powerswitch lets you check if you could save money on electricity and gas. Just enter your details into the calculator to find the cheapest energy deals.