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Hot water systems and water use

Many New Zealand households spend more on heating water than on heating their home (EECA).

The type of hot water system and how you use water in your home are important considerations to help reduce energy and water consumption.

The BRANZ House Condition Survey records information on the types of hot water systems present in New Zealand houses. It also provides data to help understand how efficiently water is being used in the home, for example whether cylinders and pipes are insulated, evidence of leaking taps, temperatures at the hot water tap and the rate of flow in the shower.

Shower flow rates

The flow rate from your shower can have a significant impact on your hot water use and therefore energy bills. The Energy Efficiency and Conservation Authority (EECA) recommends a flow rate of less than 9 litres per minute.

Shower flow rates are recorded in the House Condition Survey by timing how long it takes to fill a 4-litre bucket with water from the shower at normal temperature. The results (converted into flow rates in litres per minute) show that nearly half of all showers measured in the survey exceeded the EECA recommended rate. Reducing the flow rate by just 1 litre per minute could save around $80 a year for a household of three. For more information on reducing your hot water use, see EECA's Energywise website.

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Almost half (49%) of showers tested had a flow rate that exceeded the maximum flow rate of 9 litres per minute recommended by EECA.  

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15% of showers exceeded a flow rate of 15 litres per minute. For each 5-minute shower, that's 30 litres more water used than if the flow rate were reduced to the recommended rate of 9 litres per minute. 

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Reducing the shower flow rate by just 1 litre per minute could save 5 litres of water for every shower. For a household of three over a whole year, that could save the equivalent of around 5 spa pools. [Assumes shower time of 5 minutes. See Shower head calculator]

Leaking taps 

Leaking or dripping taps not only waste water but can represent significant yet avoidable costs if hot water is being lost. The BRANZ House Condition Survey records evidence of leaking taps and leaking showers (with capacity to assess up to three bathrooms in any one house). The results show over 9% of houses surveyed had a leaking tap or showerhead. Wellington Water estimates that a tap dripping every few seconds could add up to around 28 litres every day, which, over three months can amount to up to 2,500 litres

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9% of houses had signs of a leaking tap or showerhead. If left over a whole year this could be enough to fill a small swimming pool. 

Hot water tap temperatures

The New Zealand Building Code states the maximum water temperature at the tap for showers, baths and hand basins in the home should be 55°C. Hotter than this risks scalding household occupants. Whilst 55°C is the maximum for all homes, in some places (e.g. where young children are present) the temperature should be no higher than 45°C at the tap.

The House Condition Survey records the temperature of the hot water tap in all bathrooms. The results show that in 31% of the houses surveyed the measured temperature exceeded 55°C.

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Hot water temperature at the tap exceeded the maximum of 55°C in 31% of houses surveyed

Hot water cylinder thermostat settings

If hot water is sourced from a cylinder, the cylinder thermostat temperature should be set to 60°C. This is hot enough to kill harmful bacteria in the stored water, such as legionella, but not so hot that it risks scalding temperatures at the tap. Heating hot water cylinders beyond 60°C also wastes energy and money.

The average temperature of all cylinder thermostats recorded in the HCS was 62°C. However, this ranged from a minimum of 40°C to a high of 85°C. A quarter of houses surveyed had a cylinder set at 65°C or higher, and one in ten were set at 70°C or higher. [These results are based on a subset of the complete HCS dataset (i.e. smaller sample size) as nearly one-fifth of houses surveyed did not have a cylinder and in nearly one-third of houses the thermostat setting was not accessible/readable at the time of the survey.]

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Hot water cylinder and pipe insulation

Insulating the hot water cylinder and first metre or so of hot water pipe coming off the cylinder helps keep the heated water warm, reducing energy (and therefore cost) required to heat it. Whilst modern cylinders may have insulating material by design, older cylinders (pre-2002) are likely to be poorly insulated and need wrapping (Saving money on hot water).

The House Condition Survey records the presence of a hot water cylinder wrap and hot water pipe insulation. Results show two-thirds (66%) of hot water pipes lacked insulation and four-fifths (79%) of cylinders were not wrapped. Depending on the age of the cylinder and pipes, adding insulation could save $80 a year on your energy bill, yet costs only around $60-70 to install (Saving money on hot water).

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