What are the most eco-friendly heating options this winter?

Log burners

Why: Newer models of log burners can function in a much more eco-friendly fashion than traditional burners. The net carbon emissions of a log burner are zero - provided your wood supply comes from a renewable resource - as it is simply releasing the carbon which has been sequestered into the growing timber. Burners work best when they are fired with dry wood, rather than damp wood, which improves efficiency and minimises pollution.

How: If your home has a good thermal envelope - the ability to retain heat with insulation or window glazing - log burners can be a very efficient means of heating. They can even be fitted with a wetback to heat water, allowing for yet more energy efficiency and power savings.

Cost: Log burners range from about $1500 to many thousands, but they can be very cheap to run if you use good-quality wood. Improving the thermal envelope of your home can increase the efficiency of the log burner further, which will make it a better investment.

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Heat pumps

Why: For every kilowatt of energy that a heat pump consumes in an hour, an average of three kilowatts of heat will be generated - an incredible gain from minimal use of energy. On average, 75 per cent of our electricity comes from a renewable resource. The figure for Auckland, however, is in the region of 36 per cent, so some of the electricity used in your heat pump will have been generated by the burning of coal or gas, giving it a small carbon cost.

How: Heat pumps are particularly efficient because the outside unit simply draws heat from the external air and transfers it to units inside the home. This is much more energy efficient than if the unit was generating heat itself.

Cost: Installing a cheap single-unit heat pump generally costs around $1000. A multi-unit system can cost from around $2000, but will allow a larger area to be heated. Regardless, the costs will be made up for in energy savings, thanks to heat pumps being so efficient.

Pellet fires

Why: Pellet burners are fired using sustainably sourced pellets made from recycled sawmill waste, including shavings and sawdust. The pellets burn very cleanly, making them carbon neutral, producing no negative effects for the community and environment. There will, however, be a minor carbon cost to the actual production of the pellets.

How: Because the pellets are loaded into the back of the burner and automatically fed into the fire, you can have precise control over the rate of burning and the strength of the fire. Some pellet fire installations can even be controlled with a thermostat, or switched on and off with a timer. For this reason, pellet burners are the most efficient environmental option when it comes to indoor fires.

Cost: The downside of pellet burners is that they're expensive. A single-storey flue starts at around $4000 to buy and install, with the added expense of buying the pellets.

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Insulation

Various types of insulation can have significant effects on the efficiency of home heating systems. Glass, wool and polyester insulation can all be placed in ceilings, walls and under floors, as a new or retro fit installation.

Glass insulation provides thermal resistance of ~R2.5 per 100mm; wool gives ~R1.8-2.3 per 100mm in blanket form; and polyester gives R1.8-2.0 in its low-density form.

Glass and wool can both contain high proportions of recycled fibre, either from New Zealand or overseas, depending on the plant of manufacture. Polyester is petrochemical-based - derived from petroleum.

Whilst the World Health Organisation used to say glass fibre was a carcinogenic, it has now removed that classification. Glass and wool come out as being the best types of installation when considering eco-friendliness.

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