Energy efficiency of electric water heaters (ErP)

Since 26 September 2015, all TESY water heaters are equipped with energy efficiency labels in conformity with a new ErP (energy related Products) Directive of the European Union. The energy efficiency labels attached to the various domestic appliances enable the consumer to take an informed decision when making a purchase. They contain information about the consumed electric power on an annual basis, the type of the appliance and a number of its other features.

Energy label

The energy label has an equal outer appearance in all EU member states and is language neutral. The information is conveyed through pictograms, which substitute the text in the different languages within the Community. The black arrow shows the energy efficiency class of the specific appliance under the EU Directive. The color arrows with letters specify the different classes of energy efficiency. Dark green corresponds to the most energy efficient class, whereas red identifies the class with the lowest energy efficiency

Thanks to the energy label, the consumer can now choose an appliance of the highest possible energy efficiency, thus saving on electricity and water bills and contributing to the protection of environment through reduction of carbon dioxide emissions and the use of less resources like electric power and water.

Parameters to be stated only for the electric water heaters

ANNUAL CONSUMPTION OF ELECTRIC POWER in kWh per year or AEC (Annual electricity consumption) specified in kWh/annum (parameter from the energy label) This is the consumption of electric power on an annual basis, as measured in laboratory conditions. The parameter is comparable for all electric water heaters, sold on the territory of the European Union and may help you calculate the approximate difference in your annual expenses for electric power, if you used different brands of electric water heaters. The annual electricity consumption (AEC) can only be compared between appliances of brands with identical drain profiles (M, L, XL, etc.).

MANUFACTURER-SET TEMPERATURE FOR ECONOMY / COMFORT OPERATIONAL MODE - Tout of box (parameter from the product leaflet) In some models of electric water heaters, the most energy efficient mode of work providing sufficient amount of hot water is when the temperature is set to a level, which is lower than the maximal admissible one. Such a mode can be reached at a temperature of 65℃ or even 60℃. It is this temperature enabling the attainment of the highest energy efficiency class that is designated as Tout of box.

MAXIMAL TEMPERATURE, AT WHICH THE ELECTRIC WATER HEATER’S THERMOSTAT CAN BE SET - Tmax (parameter from the product leaflet) Apart from Tout of box, the manufacturer is also obliged to declare the maximal temperature, at which the thermostat can be set (Tmax), and which sometimes differs from Tout of box.


(parameter from the product leaflet)

   As it is perfectly possible two similar in size electric water heaters of different brands to provide substantially different amount of warm (mixed) water for domestic use, the European regulating authority requires from manufacturers to state a parameter measured in identical laboratory conditions and using a strictly prescribed methodology. V40 is measured in litres (L) and shows the amount of warm (mixed) water with a temperature of 40℃, which can be drained from a switched off electric water heater after the water in the appliance has been heated to the declared Tout of box For water heaters with volume capacity of up to 36 litres, this parameter is not to be specified. V40 is a comparable parameter, if declared with one and the same Tout of box.

What is it that affects the amount of hot water provided by an electric water heater?

Inarguably, the net volume of the water tank is of significance for the amount of HHW, (hot household water), but in practice it is not the only factor. Apart from the appliance’s volume capacity, the quantity of hot water very much depends on how fast the incoming cold water is mixed with the hot water already in the heater during use. This process can be optimally managed by an inbuilt nozzle with PISTON effect. Its function is to let the cold water pass through, without allowing its fast mixing with the hot water. The electrical water heaters equipped with the innovative PISTON effect ensure more hot water and comfort. Another important factor affecting the amount of hot water is the temperature, at which the heater works. The water heaters ensure the greatest amount of HHW when their thermostats are set to the maximal temperature.

Parameters to be stated only for the indirect heated storage water heaters

(parameter from the energy label)
For the indirect heated storage water heaters, a parameter must be stated that shows the energy losses through the appliance’s insulation for a period of 24 hours, measured at strictly defined laboratory conditions.
(parameter from the energy label)
The manufacturer must state the exact volume that the water heater can store.