Appliances
Pellet burners
Introduction
Pellet burners have some real advantages – if you can source pellets at a reasonable price.
There’s plenty to like about pellet burners. They’re convenient to use and an effective form of low-pollution carbon-neutral heating. But the high cost of the pellets in some areas has slowed the take-up of these heaters.
We take a look at how they work, their pros and cons, and include a database of 26 models tested for emissions and efficiency.
Different from a woodburner
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 (pictured right), 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.
In some models, a thermostat can be used to keep an even room temperature – and a timer can provide automatic switching-on and -off.
In freestanding and fireplace-insert models, a hopper load of pellets lasts for around 24 hours of continuous burning – and these models produce a similar amount of heat to a conventional woodburner. Basement furnace models product much more.
Running costs
Shop around for the cheapest source of pellets – there are big variations in price. If there's a pellet mill close to you, try them first.
To get a good price, consider buying a year’s worth of pellets.
Rule of thumb
The dollar cost of a 20kg bag of pellets roughly equals the running cost in cents per kWh. So – for example – a 20kg bag of pellets at $12 a bag will give you heating at 12c per kWh; a $15 bag would work out at 15c per kWh.
If you can source pellets from the mill at $450 per tonne (the equivalent of $9 per bag), running costs are 9 cents per kWh.
Checklist
If you are thinking of buying a pellet burner, here's what to consider.
Furnace
Fireplace-insert pellet-burners produce as much heat and are as efficient as freestanding models. To distribute heat throughout the home basement-furnace models are connected to water-filled radiators in the house, to under-floor heating, or (via a heat exchanger) to standard central-heating air-ducts.
Wetbacks
Some models can be installed with a wetback (water heater). This can reduce your hot-water bill (but possibly not enough to recoup the wetback's expensive installation costs).
Heat output
The maximum output of most pellet burners installed in a living room is in the 9 to 11 kW range. But overheating the room is less likely with a pellet burner because the heat output is controllable over quite a wide range – usually 1.9 to 11 kW.
Controls
Pellet-burner controls – the on/off switch, start button, and heat-control knob – are electrical.
Cleaning
Pellet fires produce less ash than a conventional woodburner. Weekly emptying of the ash tray and cleaning out the burner is usually enough. Most models have a pull-out ash tray.
Flue system
Flues are typically 75mm in diameter (smaller than a conventional woodburner's). Flue arrangements can be varied: fireplace-insert models can have their flue inside an existing chimney; freestanding models often have their flue exiting the room horizontally through an exterior wall and then running up the outside of the house.
Installation costs
Every house is slightly different, but installation costs should be similar to those of a woodburner. Remember there needs to be a power outlet nearby.
Safety guards
The surfaces of a pellet burner can get very hot and be a danger to small children. Protective guards are available and highly recommended.
Building consents
You must obtain a building consent from your local authority before you install a pellet burner.
Running costs
Running a pellet burner costs around 8c to 15c per kWh (see Different from a woodburner for more information). The top of this range is about double the cost of running a woodburner (using bought firewood) or a heat pump, but less than half the cost of running a conventional electric heater.
Depending on fuel prices in your region, a pellet burner may also be competitive with a reticulated (flued) gas heater or central heating.