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Electric mini-tank water heater or instant water heater?
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Comparison of a mini-tank storage water heater and electric instant water heater
In this article we compare compact electric storage water heaters with instant water heaters.
What kind of solution to chose for small needs as the sinks, washbasins, showers? We pay very little attention to the consumption regarding the production of domestic hot water (DHW). Even if the housings are better and better insulated and so the needs in heating keeps decreasing, the needs of DHW change only very little. In all cases, the rule to adopt for these compact solutions is to place them the closest way possible to the water drawing point.
Electric mini-tank storage water heater
 mini-tank water heater |
Electric instant water heater
 Ariston design instant water heater |
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| Specialisation | (+) Whatever your needs are, a weak flow (washbasin) or more significant flow (kitchen sink, shower), the tank has a constant efficiency as long as it’s not empty
(-) Needs a security group and an air bleed circuit |
(-) Depending of the use the required flow is variable (washbasin 2 litres per minute, sink 5 litres per minute, shower 8 litres per minute). This implies the water heater to be perfectly sized for the need in order not to have lukewarm water or variable temperature. Requires a high instant electric power (around 8-9 KW – beware of the dimension of your electric installation and the cost of complementary subscription if needed)
(+) Does not require any installation of security group (and thus a connection to a drain pipe) contrarily to a hot water tank |
| Operation offered | (-) Risk of operation disruption when the tank is empty
(- / +) Time period to heat water again (subject to models, very reduced for small volumes – 30 mn) |
(+) No risk of hot water disruption (continuous operation) and instant operation
(+) No risk of water hygiene because there is no storage (-) According to the regions, in winter the water from water service reaches 5-6°C to 10°C, in summer 12-14°C. This means that the water heater must produce a sufficient quantity of energy to heat with a variation of at least ∆T=40°C for the shower. All the devices do not have this capacity. In the case of a shower, this element is essential |
| Consumption | (-) We heat water at a constant temperature (between 55°C-65°C) which is superior to the needs. Waste of energy
(-) Unavoidable energy losses when the water is being stored (heats the room even in summer) (-) Déperditions énergétiques inévitables quand l’eau est stockée (réchauffe la pièce même en été) |
(+) Significant electric consumption but only for a little while (the time of water drawdown)
(+) According to the use, we heat water at a lower temperature than with a tank. Washbasin (35°C), Sink (48°C), Shower (40-45°C). Adjustable target temperature. (+) Zero heat loss because there is no water storage (-) No possibility to benefit from off-peak rates |
| Maintenance, lifetime | (+) Longer lifetime than a boiler
(+) Zero maintenance or very reduced (resistance) (+) Great reliability |
(+) Zero maintenance or very reduced (resistance)
(+) No risk of tank perforation at the end of its lifetime because there is no water storage (+) Longer lifetime than a boiler (+) Great reliability |
| Compactness, Design | (+) Sometimes a more elaborated design | (+) Very compact (under the sink, in the cupboards, etc) |
| Prix | (+) Purchase price (between £200 and £500 excluding installation) | (+) Purchase price (between £200 and £500 excluding installation). Lower operation costs |
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