Pellet burners

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.

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.

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 produce much more.

Running a pellet burner costs around 8¢ to 15¢ per kWh. 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.

Shop around for the cheapest source of pellets – there are big variations in price. If there's a pellet mill close to you, try there 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 12¢ per kWh; a $15 bag would work out at 15¢ per kWh.

If you can source pellets from the mill at $450 per tonne (the equivalent of $9 per bag), running costs are 9¢ per kWh.

Compared to sources such as 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.

In the past few years pellet burners have enjoyed a reasonable uptake, but the market remains small compared to other heating options. The limited number of wood pellet suppliers (often only one per town or city) means that if a pellet manufacturer in your area goes bust, pellets could become prohibitively expensive. We recommend you ensure there is a well-established pellet supplier near you before investing in a pellet burner.

• 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.
• 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.
• 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).
• 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.
• Controls: Pellet-burner controls – the on/off switch, start button, and heat-control knob – are electrical.
• 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.
• Thermostat: Allows the room temperature to be automatically maintained at a set temperature.
  
• Timer: Allows the fire to be automatically started and stopped at pre-set times.
• 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.

Installation

• 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.
• Building consents: A building consent is required to install any solid fuel space heater (woodburners, pellet burners, and diesel burners). The requirements vary between regions – check with your local council to find the requirements in your area. Some regions have more stringent regulations due to recurring air pollution issues, especially Nelson and Christchurch where low emission burners are mandatory.