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Water Efficiency Labelling and Standards
(WELS) Scheme

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Download the guide

• Water Wastage of Instantaneous Gas Water Heaters (PDF - 1909 KB)

Summary

Eight instantaneous gas water heaters (IGWHs) were tested, including:

• a mechanical ignition type
• a number of electronic ignition types
• types designed for external mounting
• a type designed for internal mounting
• a range of capacities
• different (current) energy star ratings types.

These IGWHs were tested to determine the quantity of water which flowed through the test unit from the time the unit was turned on until the time the flow from its outlet reached an appropriate temperature differential relative to the final steady state temperature of the water.

Each of the test water heaters were installed in accordance with the manufacturers' instructions and instrumentation appropriately connected. A data logger was used to collate the data. The test procedure which was applied closely followed the test method specified in Australian Standard AS 4552: Gas fired water heaters for hot water supply and/or central heating.

The quantity of water which flowed through the test unit until the water reached a steady state temperature was measured for a variety of water temperature settings, water pressures and water flow rates. The water which was wasted was determined from the data logger information using temperature differentials of 5ºC and from the average steady state temperature as the reference criteria.

The study found:

1. Instantaneous gas water heaters wasted substantial quantities of water and there were significant differences between water heaters in respect to the quantity of water wastage – enough to warrant these products being considered for inclusion in the WELS program. Under some (normal) conditions it was found that at the 5°C and 1°C temperature differentials, 64.6 L and 93.1 L of water was wasted daily.
2. The set up and test procedure for ascertaining water wastage should be the same as that specified for determining gas consumption.
3. The quantity of water wasted should be determined independent of gas consumption determinations, until there is positive evidence that water wastage, as determined from theoretical calculations using gas consumption data and that determined directly are equivalent.
4. Water wastage should be determined using at least:
   1. the maximum water flow
   2. the highest temperatures rises obtained without and with (if available) a remote temperature controller
   3. the standardised pressure of 320 kPa
   4. a reference temperature differential that is 90% of the steady state temperature.
      The reference differential should not exceed 5ºC.
5. To account for additional quantities of water wasted by some heaters that have a heating profile which oscillates substantially (with ever decreasing amplitude) around the steady state temperature until the steady state is reached, the water which is wasted should be determined not from a point on the initial rise of the temperature curve but from a point on the curve that is equivalent to the reference differential temperature, immediately before the steady state temperature.
6. Although the quantity of water wasted from an instantaneous water heater would be more realistically determined from data taken from a distant draw-off point (e.g. a shower that is connected to the heater via typical plumbing), rather than taken from the heater outlet itself, it is suggested that water wastage should continue to be determined from the outlet of the heater, so as to maintain parity with storage water heater procedures.
   
   Not all of the water will actually be wasted, as some end-uses (such as for bathtub filling or washing machines) will retain and use initial, below-temperature flows. For the purposes of the study, all wastage is assumed to go to drain. In future, monitoring of actual end use patterns is recommended in order to establish data on actual percentages of start-up losses wasted to drain.