The large amount of radiant heat produced by a wood-burning fire 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.
By burning dry wood in a clean-burning woodburner you win 3 times over:
- Wood is a sustainable heating fuel.
- You get more heat from a clean-burning (non-smoky) fire.
- Cleaner burning means fewer smoke particles lodging in all our lungs.
That’s the positive stuff. The flip side of woodburners is their contribution to air pollution and their relative lack of convenience.
If you burn wood carelessly or burn wet wood you can create a health hazard through ultra-fine pollution lodging in people's lungs. Modern woodburners can burn much more cleanly than older models. But our tests have shown that clean burning only occurs if the fire is carefully tended – and with the right-sized dry wood.
Air pollution is not inconsequential. The ultra-fine soot particles in wood smoke are a health hazard. They can lodge deep in the lungs causing premature death, hospitalisation and respiratory illness. It’s not just the people of Christchurch and Nelson who are at risk: there are many monitored areas (“airsheds”) where there are health risks from wood-fire pollution.
Woodburners aren’t as convenient as heat pumps or central heating systems. You “regulate” the room temperature through the amount of wood you burn and there’s no timer-controlled automatic starting system. You also have to buy firewood in advance and store it.
If you're about to buy a woodburner, here's what to consider:
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.
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 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. This has to be on every woodburner that's sold – and it states the tested heat output, along with the efficiency and emissions rate.
Convector vs radiant
All woodburners both heat the air and radiate heat on to objects that are within a few metres of them. But some woodburners are marketed as predominantly one type or the other. It depends on the external design of the firebox. Convectors are best for well-insulated non-draughty houses with low ceilings. Radiant-type models suit older and less-well insulated (or draughty) houses with higher ceilings.
A convector heater heats the air immediately around it. Hot air is lighter (less dense) – so it rises away from the heater and gets replaced with cooler air which is in turn heated. This convection air-current means that the warmest air in the room ends up near the ceiling with the coolest air near the floor. Convector heaters are air warmers.
A radiant heater “shines” heat on to anything in its path. That could be you if you’re near the fire, or furniture within a few metres of the fire.
The controls should operate smoothly, and it should be relatively easy to clean the outer surfaces and empty the firebox.
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.
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.
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.
Woodburner surfaces can get very hot and can be a danger to small children. Protective guards are available, and highly recommended.
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.
A poor woodburner installation job can ruin the heating and emissions performance of the best models. Check that your woodburner installer has New Zealand Home Heating Association certification or is otherwise suitably experienced.
A heat-transfer kit usually removes warm air from the lounge and ducts it to a colder part of the house. Alternatively it can be set up to duct cold air from elsewhere in the house and deliver it to the lounge for heating. Either way the doors must be left open or ajar so that the air can circulate and even out the temperatures.