As winter approaches, a water heater that delivers hot water efficiently and safely is a necessity for many a household.
But given the many choices of water heaters in the market, it is no easy task to find one that fits the bill all round in performance and safety as well as ease of use.
The Consumer Council, in collaboration with the Electrical and Mechanical Services Department (EMSD), has tested and evaluated 12 models of household electric storage water heaters.
Included in the test were 6 models of the unvented type (also called central type) and 6 models of shower type (open-outlet type).
The former can be connected to multiple hot water taps (e.g. bath tubs, wash basins) while the latter can only be fitted with one unblocked showerhead without any on/off control valve.
In the test, the samples were rated overall based on: performance (60% on energy efficiency, preheating time, average temperature and maximum time of hot water delivery), safety (30%) and ease of use (10%).
On a 5-point overall rating, 2 samples of the unvented type were awarded 4.5 points and 4 samples scored 4 points. For the shower type, 2 samples achieved 4.5 points, 2 samples scored 4 points and the remainder 2 received only 3.5 points.
On safety, the test results indicated that all 12 samples were in compliance with the major requirements in the safety standard IEC60335-2-21.
In particular, all 6 unvented samples scored fully in overall safety rating, while only 2 of the shower type reached the same level in safety.
3 of the shower type samples received a slightly lower 4.5-point overall safety score. In a safety test which simulated the rare event of abnormal operation conditions of faulty thermostat and no water supply leading to an abnormal temperature build-up, the overheating resulted in damage to the samples' electrical insulations.
For the remainder one shower type sample, it received only 3.5 points in overall safety due to insufficient clearance and creepage distances at some internal parts, and unsatisfactory fire resistance of the plastic enclosure.
In October last year, a shower type electric water heater in a residential flat exploded. It was suspected that the accident was caused by the faulty thermostat and the installation of an on/off control valve at the water outlet.
Consumers are strongly advised that the water outlet of a shower type heater must remain unblocked. Never install an on/off control valve at the water outlet of the heater or connect the outlet to a basin or tub, to prevent excessive high pressure build-up inside the tank that could result in explosion.
On performance, the test results revealed considerable variations in energy efficiency - the higher the efficiency the less energy consumed in stand-by condition - which is both an environmental concern and impact on cost increase in electricity.
Under the grading criteria of EMSD's Energy Efficiency Labelling Scheme, 3 of the samples would have been awarded the top score Grade 1 on the basis of the test. 3 other samples would receive only the least score Grade 5.
The samples were compared also for their delivery of hot water. Under the test condition, a sample's thermostat was set at 65℃ and switched off after preheating. For the unvented type, the average temperature of hot water delivery ranged from 40℃ to 58℃, while the shower type from 46℃ to 63℃.
For the maximum time of hot water delivery (measured with the thermostat set at the maximum and hot water delivered at 50℃ and 5 litres per minute until the temperature dropped to 40℃), the unvented type was found to range from 8.6 to 17.3 minutes while the shower type from 5.1 to 13.6 minutes.
Other safety advice for users to observe:
- The installation and alteration of any electric water heater must be carried out by a registered electrical contractor and a licensed plumber.
- If any bnormality is found, switch it off immediately and arrange inspection by an experienced technician.
- Switch off the heater after use; and arrange for regular inspection to maintain the device in safe condition.
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