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Performance of Electric Storage Water Heaters Vastly Varied Based on Capacity and Type Advocating for Upgrading Energy Efficiency Labelling Scheme to Cover Double-Tank Models

  • 2024.01.15

After a hard day’s work, many people enjoy having a hot shower to rinse off fatigue. When using an electric storage water heater, the heating speed, duration of continuous hot water supply, safety, power consumption, and price are the 5 major consideration factors when making a purchase. The Consumer Council and the Electrical and Mechanical Services Department (EMSD) tested the performance and safety of 12 models of electric storage water heaters on the market, including single-tank and double-tank, shower type and unvented type models. As the rated capacity of models vary considerably from 14L to 35L, the Council compared the models based on their “per litre of capacity” to ensure that tests were objective and fair. The rated power input of all models was 3,000 watts, and after testing, the heating speed per litre of capacity did not vary much among models. Simulating consumers’ showering habits, the volume of 40°C hot water supply and the duration of continuous hot water (40°C to 45°C) supply were measured, and in both scenarios shower type models were found to have a better overall performance. In safety tests, the overall performance was satisfactory, except for 2 shower type models which failed the abnormal operation test. When using a shower type electric water heater, consumers must ensure that the heater is installed with proprietary or manufacturer-approved mixing faucets and shower heads, and must not install any on/off control valve at the water outlet or the shower head. Otherwise, the water tank may explode due to excessive pressure.

The performance tests were conducted in accordance with the latest edition of the IEC standard. The energy efficiency performance of 3 single-tank models was found as not conforming, whereas the measured standby power consumption of double-tank models was higher than that of single-tank models. In view that many double-tank electric water heaters are now available on the market, the Council recommends EMSD to include them in the Mandatory Energy Efficiency Labelling Scheme (MEELS) as soon as possible, so consumers can make informed choices. The 12 electric storage water heater models tested by the Council included 6 shower type and 6 unvented type models, while 7 were single-tank models and 5 were double-tank models, with prices ranging from $1,280 to $6,980 (excluding installation fees). The 2 models with the highest ratings were both priced at around $3,000, reflecting that product quality and price are not necessarily correlated.

Similar in Heating Speed

Shower Type Models Performed Better in Continuous Hot Water Supply

When using an electric storage water heater, consumers are the most concerned about whether there is enough hot water for showering, and the heating time required. The time required for supplying hot water with a temperature rise of 50°C was measured. In terms of heating time per litre of capacity, shower type models ranged from 1.12 minutes to 1.28 minutes, while that of unvented type models ranged from 1.07 to 1.37 minutes, which were similar in overall performance. The rated capacity of the tested models ranged from 14L to 35L, and the actual total heating time ranged from about 17 to 42 minutes among the models. For the same design, the larger the capacity, obviously the longer the heating time required.

Tests also simulated a shower in winter with a water flow rate of 5L per minute and measured the duration of continuous supply of hot water (40°C to 45°C). Shower type models performed better overall, with continuous hot water supply ranging from 0.41 minutes to 0.54 minutes per litre of capacity, among which 3 models reached 0.5 minutes or above, while that of the unvented type models ranged from 0.3 minutes to 0.4 minutes. However, even for the model with the capacity up to 35L and longest duration of continuous hot water supply, the actual duration of hot water supply was less than 15 minutes, while that for models with less capacity was found to be as short as 6.6 minutes. To prolong the duration of hot water supply, consumers may consider using shower heads with a lower water flow rate that is compliant with specifications.

In another test, cold water was heated up in the water heater models to their maximum water temperature, then the maximum volume of hot water (40°C) supplied was measured while the power was kept on. Results showed that the hot water quantity for unvented type models ranged from 1.52L to 2.09L per litre of capacity, while shower type models once again performed better, ranging from 1.98L to 2.47L.

Double-Tank Models Had Higher Standby Power Consumption

Advocating for Inclusion into the Energy Efficiency Labelling Scheme

Many people habitually keep their electric water heaters on for long periods in winter to have hot water always available. In the test, the thermostats of the models were set at 65°C, and the power consumption in standby mode for a long period (no less than 48 hours) was measured. It was found that the measured standby power consumption per 24 hours ranged from 0.35 kWh to 0.85 kWh for single-tank models, and from 0.95 kWh to 1.8 kWh for double-tank models, revealing that double-tank models had higher standby power consumption than single-tank models. Assuming an electric water heater is in standby mode for around 5 hours per day (i.e. 1,800 hours per year), and based on an electricity tariff of $1.7/kWh, the estimated annual electricity cost for the shower type single-tank models would be $44 to $103, while that for the double-tank models would be as much as $157 and $161 respectively; for unvented type single-tank models, the estimated annual electricity cost ranged from $87 to $108, while that for the double-tank models was from $120 to as high as $229.

The test was conducted in accordance with the latest edition of the IEC standard. Among the 7 single-tank models, 3 were found with a discrepancy between the measured standby power consumption and the rated values previously submitted by their agents to the EMSD that exceeded the permissible discrepancy limit (+5%) of the MEELS. As for energy efficiency grading, the calculated energy efficiency grading for 2 models were Grade 4 and Grade 2 respectively, which were both 1 grade lower than indicated on their energy labels (Grade 3 and Grade 1). The relevant results have been forwarded to the EMSD for follow-up.

To boost energy efficiency, EMSD conducted a consultation in August 2023 on the grading of washing machines, refrigerators, and electric storage water heaters. Based on recommendations in the consultation documents and test results conducted in accordance with the latest edition of standards, the Council found that only 1 out of the 7 single-tank models could maintain a Grade 1 rating. However, as the proposed grading requirement are not yet implemented, the results are for reference only. The Council supports the EMSD’s policy and measures in enhancing the energy efficiency grading and anticipates that the EMSD will adopt the latest version of IEC 60379 as soon as possible, and to include double-tank electric water heaters in the MEELS, to facilitate consumers in making accurate comparisons of the energy efficiency of different types of electric water heaters.

2 Shower Type Models Failed 1 Safety Test

Apart from performance and power consumption, the safety of electric water heaters must not be overlooked. The EMSD conducted safety tests including abnormal operation, protection against access to live parts, and markings and instructions, etc.  2 shower type models did not pass the abnormal operation test. The test simulated the malfunctioning of the electric water heater’s thermo control, and the inner tank was either without water or filled with water to a level slightly higher than the heating element while operating at 1.15-time or above the input power. 2 models were found with minor damage to the heating element, failing to comply with the standard requirements, but it should not pose safety hazards under normal operation.

Manufacturers Urged to Improve Installation and After-sales Services

Most of the complaints about electric water heaters received by the Council in the past 3 years were related to repair, maintenance, and installation services, with water leakage of the inner tank being the most common problem. The full warranty of the tested models ranged from 1 to 3 years, while the warranty of inner tanks were longer, ranging from 2 years to life-time. However, if water leakage of the inner tank occurred after the full warranty had expired, consumers still had to pay on-site inspection charges even if the inner tank was still within its warranty period. In addition, only a small number of models provided warranty renewal services, with annual fees ranging from $480 to $680. To promote sustainable consumption, the Council urges agents and retailers to extend warranty periods with a more reasonable price package.

Consumers may refer to the following tips when purchasing and using electric storage water heaters:

  • There are 2 types of electric storage water heaters, namely unvented type and shower type, which have different operation principles, installation and usage. Consumers can consider their household environment and family size to choose the right type and water storage capacity;
  • When purchasing a single-tank electric water heater, consumers can refer to the energy label of the product and choose a model with higher energy efficiency. The power should be switched off immediately after use for safety and energy-saving;
  • Shower type electric water heaters should only be installed with proprietary or manufacturer-approved mixing faucets and shower heads. Do not install any on/off control valve at the water outlet or shower head, and do not connect to the wash basin or bathtub. Otherwise, once the tap is turned off, pressure release will be blocked and the water tank may explode due to excessive pressure;
  • Check the temperature and pressure relief valves of unvented type electric water heaters regularly to ensure there is no obstruction or damage by foreign objects;
  • Never install or modify an electric water heater by yourself. Should there be any abnormal conditions, such as circuit breaker tripping, abnormal emission of steam from the shower head or the pressure relief valve drain pipe, stop using the water heater and switch the power off immediately, and engage a registered electrical contractor for inspection and repair.


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