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23 November 2020

Is Using Gas to Heat Buildings and Hot Water a Low Carbon Option in NZ?


How do the greenhouse gas emissions of different fuels compare?

These emissions vary considerably between different countries. Therefore, heating systems that make perfect sense in one country may not make nearly as much sense in another. For example, in Australia if a building or home uses electricity instead of gas for heating and domestic hot water (DHW), it will be emitting up to 4.7 times MORE greenhouse gases (GHG) than directly burning fossil fuel gas in a boiler or instant water heater.

This is because in Australia a large proportion of electricity is generated by coal-fired power stations. The GHG emissions in the most populous Aussie states (NSW, VIC, ACT, QLD) for electricity are relatively high at 0.87 kgCO2e/kWh, whilst burning gas has emissions of 0.19 kgCO2e/kWh.

There is a similar but slightly less extreme picture in the UK, where electricity is 1.3 times more carbon-intensive than directly burning gas (0.23 electricity vs. 0.18 gas, kgCO2e/kWh).

In this context, the logic of using efficient gas appliances makes reasonable sense, especially as we transition to even more sustainable and lower carbon heating options in future.

If we apply the same logic in NZ, do we get a similar outcome?

In NZ, natural gas has emissions of 0.195 kgCO2e/kWh (LPG is worse at 0.222), whilst our electricity is around 85% renewable and so has emissions of only 0.097 kgCO2e/kWh. This makes electric appliances 50% LESS carbon-intensive than using a gas appliance.

Therefore burning gas, no matter how efficient the gas appliance, has at least twice as much negative environmental impact in New Zealand as using readily available alternatives.

Electricity is the clearest direct alternative to gas (natural and LPG), with distribution throughout both islands and GHG emissions half that of burning gas in NZ.

Combining electricity with a high-efficiency solar thermal system or heat pump makes the numbers even better, with an average efficiency of x 3 for standard heat pumps and up to 5 for CO2 heat pumps. With the choice between standard electric hot water cylinders and hot water heat pumps, most heating and DHW loads in a home can be met without using gas. These systems apply to larger buildings as well.

The second widely available and extremely low carbon option is wood pellets. In NZ these are 100% made from waste wood (sawdust and wood shavings mainly), with carbon emissions at a tiny 0.003 kgCO2e/kWh. This means that burning wood pellets instead of gas in any building in NZ reduces the GHG emissions by an impressive 98.5%.

Wood pellets are made in Taupo, Nelson and Invercargill, by three companies with national distribution networks and active market competition. There are a large number of distributors of high-quality pellet fires and pellet boilers that can fulfil the space heating and DHW loads of any commercial building or home. These systems can be as easy to use as a gas boiler and are very widely used in very demanding markets such as Germany, Austria and France.

Ask yourself, based on the greenhouse gas reductions we have agreed to as a society plus the easy and affordable alternatives, is there any thoughtful reason to be specifying a gas hot water or heating system in any home or building?

Get in touch with Marcus Baker at Apricus NZ Eco Energy if you want to discuss these ideas further and investigate what practical alternatives are available.
Email: [email protected]
Phone: 07 312 3382

View more information on Apricus Eco Hotwater, including contact details.
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