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Zero Carbon Central Heating and Hot Water in Residential and Commercial Buildings

Currently around 70% of the total carbon emissions from New Zealand’s buildings are emitted during their operational use¹. A large portion of these carbon emissions are for space heating and domestic hot water, especially in residential and high occupancy buildings. To have net zero buildings, owners will need to have plans in place to remove fossil fuel boilers, together with other fossil fuel combustion, such as in kitchens and use energy more efficiently.

This is completely practical with technologies currently available. It is simply that the motivation has sometimes been lacking to implement non-fossil fuel systems. Gas boilers and water heaters are widely used in new buildings and these can be directly replaced with low or zero carbon heat sources, such as wood pellet boilers, hot water heat pumps and solar hot water systems.

Wood pellet boilers

Pellet boilers can be used to supply high temperatures and volumes for central heating and domestic hot water. They can also be flexibly used in buildings of all sizes by cascading multiple smaller boilers in exactly the same way gas boilers are currently used.

There are three main benefits of wood pellet fuel:

  1. Wood pellets in NZ are manufactured exclusively from waste sawdust, therefore have the lowest carbon footprint of any fuel available in NZ, at 0.003 kgCO2e/kWh²
  2. Being made from waste materials there is an extraordinary stability in the cost of fuel with manufacturers offering up to fifteen-year fixed price fuel contracts, currently averaging at 8c/kWh for commercial customers³
  3. Wood pellets are a very practical, energy dense fuel that does not require any manual handling, being transferred by air into and inside buildings. A national network of manufacturers and blower trucks already exists, albeit under the radar of most designers and building owners, enabling easy and reliable fuel deliveries throughout the country

ÖkoFEN pellet boilers are often installed in plant rooms, in the same way as gas boilers plus a compact area for pellet storage in Flexilo bag hoppers. For buildings with limited indoor space containerised ÖkoFEN Energy Boxes are used for placement outside. The heating and DHW service connections are then run inside the building for a practical and 100% renewable heating system.

Hot water heat pumps

New Zealand is blessed with an electricity grid that is low carbon by international standards and this is projected to decarbonise further over the next 30 years. There is a rapidly increasing range of heat pump technologies that make very efficient use of this renewable electricity for heating and DHW.

Heat pumps are now available in a range of sizes for all building loads, plus new technologies enable waste heat from within a building to be harvested to dramatically increase complete system efficiency.

Innovative refrigerants are making an impact with significantly reduced global warming potential if they leak, unfortunately a reality when using refrigerants. Carbon dioxide gas is one of the most prominent of these ultra-low carbon refrigerants for DHW systems.

Reclaim CO2 hot water heat pumps use at least 75% less energy than electric or gas DHW heaters and operate efficiently at air temperatures down to -20°C. All heat pumps can be combined with a buildings’ solar PV system for further energy and carbon savings using self-generated electricity.

Solar hot water

Solar hot water systems remain an extremely high efficiency technology that makes best use of free, zero carbon solar energy for heating water. Combined with sufficient hot water storage a solar hot water system can deliver up to 75% of the DHW needs for residential and commercial buildings. The remaining energy can be provided by renewable electricity from the grid for an extremely low carbon DHW system.

Apricus evacuated tube solar hot water systems work efficiently even in overcast and cold weather because of the insulating vacuums in the tubes. The systems generate four times as much energy per square metre as a solar PV system and are entirely modular, making best use of roof space and complementing other renewable technologies for a low carbon building.

Net zero carbon heating and DHW design

Complete system design and integration with building design is an important aspect in our path to net zero buildings. Designers, engineers and owners throughout NZ are finding suitable systems for their projects with the help of Apricus Eco Hot Water, experts in low carbon space heating and DHW. Get in touch with the team at Apricus today to discuss how they can assist your journey to a net zero building. Call 07 312 3382 or email [email protected]


  1. BRANZ, average NZ commercial reference buildings Auckland, Wellington & Christchurch 2007 from NZGBC A Net Zero Roadmap for NZ Buildings, 2019
  2. Ministry of Environment carbon emissions factors, 2020
  3. Nature’s Flame offer up to 15-year fixed price pellet fuel contract with annual CPI linkage, Azwood offer up to 10 year fixed price pellet fuel contract with three review points for inflation
View more information on Apricus Eco Hotwater, including contact details.
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