If you’re designing a new home, planning a renovation or trying to reduce your household’s costs it is important to factor in how your hot water heating solution impacts the environment and what its ongoing costs are.
Did you know that heating your hot water uses an average of 45-46% of every new home’s total household energy? This makes it a crucial consideration for any modern bathroom or kitchen design and a significant opportunity to reduce energy use in your home.
Here are 6 ways of heating your home’s hot water taking into consideration environmental impact, energy savings, benefits, and drawbacks of each system in review.
1. CO2 Hot Water Heat Pump
Approx. annual energy use: 850 kWh*
Approx. annual running costs: $247*
Uses renewable energy: Yes
Approx. annual greenhouse gas emissions: 83 kgCO2e*
Pros: The lowest energy use and greenhouse emissions. Best suited when roof space does not allow for solar hot water and cylinders can be installed outside to conserve space.
Cons: Installation costs can be slightly higher than solar hot water & conventional cylinders.
CO2 heat pump water heaters absorb warmth from the air, amplify it and transfer it to heat water. They use electricity to operate the compressor rather than heating an electric element. Systems such as the Reclaim CO2 heat pump are nearly five times more efficient than a conventional hot water cylinder with an electric element. These systems can also be combined with solar PV to maximise power savings, multiplying your savings by up to 5.
View information on >> Reclaim CO2 Heat Pumps.
2. Evacuated Tube Solar Hot Water
Approx. annual energy use: 1332 kWh*
Approx. annual costs: $386*
Uses renewable energy: Yes
Approx. annual greenhouse gas emissions: 130 kgCO2e*
Pros: The next best in energy savings and greenhouse emissions with the benefit of lower installation costs. These are the best option to combine with a wetback and in off-grid homes.
Cons: The system may revert to electrical heating during periods of heavy use at night or on days with limited sunshine hours.
The solar hot water collector converts sunlight into usable heat, by passing the water continuously through the solar tubes on your roof and storing it in your hot water cylinder. The acts like a solar-heated battery, storing the energy for use when you need it later that evening and the following morning. The Apricus evacuated tube solar collectors passively track the sun, reaching peak output in the early morning and maintaining this until late afternoon. With a vacuum in each tube, these systems are extremely well insulated and operate however cold the weather, whenever there is sun.
View information on >> Apricus Solar Hot Water Systems.
3. Pellet Boiler (combined with central heating)
Approx. annual energy use: 3,995kWh*
Approx. annual costs: $479* (Domestic)
Uses renewable energy: Yes
Greenhouse gas emissions: 12 kgCO2e*
Pros: Pellet boilers are ideal for providing space heating and hot water in any home with central heating. They can warm a house using radiators and/or underfloor heating systems, plus heat the cylinder/s, hot tubs, spa pools and swimming pools. Pellet boilers are a very effective and sustainable option for larger residential and commercial buildings with high hot water demand, such as apartments, hotels and sports facilities. The larger boilers are highly automated and require minimal maintenance.
Cons: Pellets do need to be purchased for a continuous supply of energy. Smaller, domestic systems are less automated so require some weekly intervention.
A pellet boiler is a heating appliance that burns wood pellets to heat water for central heating and domestic hot water. Wood pellets in New Zealand are an easily obtainable 100% renewable fuel made from waste sawdust and wood shavings in Taupo & Nelson.
View information on the >> Easypell Domestic Wood Pellet Boiler.
4. Electric Cylinder
Approx. annual energy use: 3,995 kWh*
Approx. annual costs: $1159*
Uses renewable energy: Partially, NZ electricity is ~80% renewable
Approx. annual greenhouse gas emissions: 390 kgCO2e*
Pros: An electric cylinder is the most common and most affordable hot water system to install.
Cons: A hot water cylinder uses at least 3 times more energy than a solar hot water system and up to four times more than a CO2 hot water heat pump.
5. Instantaneous Gas
Approx. annual energy use: 4,994 kWh*
Approx. annual costs: Natural gas $699 / LPG $899*
Uses renewable energy: No
Approx. greenhouse gas emissions: Natural gas 974 / LPG 1,108 kgCO2e*
Pros: Gas califonts or instantaneous gas systems can heat hot water on demand so you will never run out, as long you have gas available.
Cons: There is a delay in starting a gas water heater, often meaning they are slower to deliver hot water than a system with a cylinder. Instantaneous gas systems burn fossil fuels which release greenhouse gas emissions and are contributing to the climate crisis. Installation costs are generally higher than a standard electric cylinder.
6. Wood Fire plus Wetback
Approx. annual energy use: 3,995 kWh
Approx. annual costs: Varies depending on cost of wood (if any) and running time
Uses renewable energy: Yes
Approx. annual greenhouse gas emissions: Between 89 to 390 kgCO2e depending on above
Pros: If you run a fire during winter, then you might as well make good use of the energy you are already producing. A wetback combined with a solar hot water system can provide almost completely free and extremely low-carbon hot water all year round. A wetback is an ideal complement to solar for off-grid homes.
Cons: A wetback is usually only useful in reducing your winter energy bill when the fire is going, compared to a heat pump or solar system which provides savings all year round. The Clean Air Act limits which fires can have a wetback, especially in urban areas. A cylinder must be near the fire and there will be significant additional installation costs compared to a standard electric cylinder.
*Energy use & approx. annual costs:
Calculated for average household hot water use for a family of four, using 200L per day, requiring 3,995 kWh of heat energy per year at standard efficiency.
*Greenhouse gas emissions: kgCO2e/year
Calculated using kgCO2e/kWh factors from MfE Measuring Emissions, 2019, assuming average annual hot water energy use of 3,995 kWh. Reclaim CO2 heat pumps have 4.7 COP, Apricus solar hot water reduces electricity use by at least 75%, published efficiency figures for gas water heaters, electric cylinder assumed to be 100% efficient. Heat loss from cylinders not included, assumed to be according to MEPS requirements and varying by cylinder size.
