FAQ | Ariston


What is the difference between a storage water heater and a instant water heater?
Both instant and storage water heaters generate hot waters, but their attributes and features differ.

There are 3 types of instant electric water heaters: mechanical, electronic and digital. The mechanical kind is the least expensive and features step-less control. Electronic type lets you control the power setting while digital type comes with a temperature display panel besides having power setting control. The instant water heater operates with a 3-3.3kw element and generally works for individual supply points, therefore if you have 2 bathrooms, you will need 2 instant water heaters. Unlike storage water heater, instant water heater does not require pre-heating before using as it generates hot water instantly. The water temperature can vary according to the water pressure. For example, if water pressure is low, the water temperature will go up and vice versa. The average life span for an instant water heater is around 3 to 5 years.

A storage water heater has an inner tank for storage of water. The capacities range from 15 litres to 100 litres. The inner tank can be made with stainless steel or copper. It operates with a 1.5kw to 3kw element and can supply hot water to more than one point (multi-point system), which means that it can supply hot water to more than 1 bathroom as well as kitchen simultaneously. A mixer is used to regulate and provide constant water temperature so it is not affected by the change in water pressure. However, the water stored need to be pre-heated before used. To save energy and prevent loss of heat, insulation is placed between the storage tank and outer casing of the heater. A storage water heater also comes with an automatic thermostat to cut off the power supply when it reaches the preset temperature. Therefore the additional electricity consumption for switching the heater on the whole day is negligible. The average life span for a storage water heater is around 5 to 7 years.
How to calculate the electricity consumption for a water heater?
Formula for calculation of electricity consumption:

Electricity cost = Power (kw) x Usage Time (hr) x Electrical Tariff

The following is a simple illustration of the consumption of 2 types of heaters on the basis of 2 users.

User 1 & 2 - uses 5 minutes of hot water each
User 3, 4 & 5 - uses 3 minutes of hot water each
Total: 19 minutes hot water required
Electrical tariff (dated Apr-Jun 2017) - S$0.2139

Electricity Consumption:
Instant water heater : 3,3kw x 19/60 x S$0.2139 = S$0.224
Storage water heater : 1.5kw x 70/60 x S$0.2139 = S$0.374

The above calculation does not take into consideration of other factors such as capacity of water heater, frequency of bath per user and original temperature of water in the tank.
How much time is required for the hot water to recover?
For instant water heater, the recovery of hot water is instant.

The recovery rate for storage water heater varies according to the power of the heater.

Initial recovery rate:
a) Inlet temperature = 25 deg C or 77 deg F
b) Bathing temperature = 42 deg C or 108 deg F

Recovery rate gallon/hour (Small capacity - 1.5kw )
= Andris/Ti Shape (1500) / 2.42x (108 - 77)
= 20 gallon / hour
= 1.3 litres / min

Recovery rate gallon/hour (Bigger capacity - 2.5kw)
= Inox/PRO R/PRO R Slim (2500) / 2.42 x (108 - 77)
= 33 gallon / hour
= 2.1 litres / min
How to choose a suitable size of water heater?
The following is a simple illustration on how to size and select a proper water heater.

  1. Normal bathing temperature = 40 deg C.
  2. Cold water inlet temperature = 25 deg C.
  3. TUV/SUD/PSB maximum allowed temperature = 77 deg C.
  4. Ariston maximum temperature setting = 70 deg C.
  5. US heater maximum temperature setting = 60 deg C.

Calculation of % of hot water required when mix with cold water:

[(mixed water) - (cold water)] / [(hot water) - (cold water)]
= [40 - 25] / [70 - 25]
= 15 / 45
= 33% of mixture is hot water (for Ariston heater)

Amount of mixed water produced at temperature 40ºC:

Ariston ( 30 litres ):
33/30 = 100/x
x = 91 litres

Ariston ( 50 litres ):
33/50 = 100/x
x = 152 litres

From the sizing program, we understand that the amount of the warm water (40 deg C) produced for bathing is not only depended on the capacity of the tank but also the pre-set temperature.

The below table may be used as a reference guide in determining a proper storage water heater for your home:



Andris Lux 15, Andris R 15, Inox AA-25

Shower & basin

Andris Lux 30, Andris R 30, PRO R 50H, PRO R 50H (L), PRO R S 30, PRO R S 40, Inox AA-40, Inox AA-50

Bathtub & basin

PRO R 50H, PRO R 50H (L), PRO R 80H, PRO R 80H (L), PRO R S 56, PRO R S 80, Inox AA-50, Inox AA-65, Inox AA-80

Corner bathtub & basin

PRO R 80H, PRO R 80H (L), PRO R S 80, PRO R S 100, Inox AA-80

What types of safety features can be found in storage water heater?
There are three safety features:
  1. Thermostat
    First level safety feature. It is of precise control of the water temperature by the user. And stop the heating process when it reaches the desired temperature.
  2. Thermal cut-out
    In case of over-heating, in the event whereby thermostat fails to work, the second sensor in the thermal cut-out provide an all-pole disconnection to the appliance from the electric supply.
  3. Pressure relief valve
    The valve is to be fitted in the inlet. The function is to prevent an excessive rise of pressure in the water tank. When pressure exceeds the 8 ± 0.5 bars, the spring in the valve will be depressed in the opposite direction to release the pressure and water will start to drip through the 4.5mm outlet on one side of the valve. This outlet should be discharge to the drainage system.
How to proper maintain a water heater to prolong the life span of the heater?
Routine preventive maintenance of water heater can provide you many years of trouble-free heater. There are several points which you should take note::
  1. Keep free from gasoline or other flammable or combustible materials around the vicinity area of the water heater
  2. It is not uncommon for the water heaters to generate hissing noise when in operation, even for the new heater. However, you should contact your professional plumber or our service center should the hissing or the noise level increases substantially as this noise may be caused by the heating element which required cleaning.
  3. The purpose of magnesium anode is to neutralize stray galvanic currents, thus preventing corrosion. Therefore, it is advisable to replace the magnesium anode in the Andris series, SL series, PRO R Slim series, PRO R SIN series and Inox AA series regularly, e.g. bi-yearly. Please call our service center for providing this service with charge.