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Water heater

The production of domestic hot water (DHW) represents 24% of the energy consumption in a home, it is important to choose efficient equipment that will ensure a lower energy consumption.


Gas water heaters are the most used equipment for the production of hot water, as they ensure good performance, with an efficiency of 88% for the entire nominal load.

These are considered instantaneous equipment because, when they are turned on, they immediately start to heat the water. However, until the water reaches the ideal temperature, it will still take a few seconds.

This period of time is one of the main points of wasting energy and water when using a water heater, and will be all the greater as the distance between the heating system and the consumption point. Another disadvantage of this type of equipment is related to the system stops because, each time the equipment is turned on or off, the alternation considerably increases the consumption of water and energy and deteriorates the equipment.

It should be noted that most of these devices do not support the supply of hot water at two points of consumption at the same time, as the power of the device does not allow the heating of such volume of water. For this to be possible, very high powers are required. If we consider the instantaneous flow foreseen for an individual shower of 0.15 L / sec, 9 L / min are spent in a conventional bath. For the supply of hot water at two points of consumption simultaneously, it will be necessary to have an equipment with twice the power, that is, an equipment that ensures the heating of at least 18 L / min.

Below are some possible flow / power combinations to determine the water heating capacity of your equipment:

Esquentador antigo

Um esquentador com mais de 10 anos, devido à sua baixa eficiência, apresenta um consumo anual de 191€.

Esquentador Classe A

Para o mesmo tipo de utilização um esquentador classe A, representa um custo anual de 154€.


Ao substituir o seu esquentador antigo por um classe A poderá obter reduções anuais nos consumos energéticos na ordem dos 37€.

Other tips
  1. Avoid using hot water for quick washes, such as washing hands or teeth, in order to avoid unnecessary energy and water consumption;
  2. Turn off the water tap while washing your teeth, hands, shaving or doing the dishes;
  3. Change baths for showers – a shower can consume about four times less water than a bath;
  4. Install temperature regulators with a thermostat, especially in the shower, as these allow you to save between 4% and 6% of energy;
  5. Set an operating temperature between 30ºC and 35ºC, which is sufficient to convey a feeling of comfort in personal hygiene;
  6. It is very important that the accumulators and the hot water distribution pipes are well insulated;
  7. Avoid leaks and “dripping” from the taps – simply dripping from a tap can mean a loss of 100 liters of water per month;
  8. Correct maintenance and a good regulation system allows total savings of over 20% in common services.
Energy label

Since September 2015, all new hot water installations must have an energy label.

The energy label applies not only to products, but also to systems, that is, to all heating solutions consisting of conventional heaters, temperature controllers and / or solar thermal systems.

How to read the energy label:

  1. Supplier name or trademark and model
  2. Supplier model
  3. Water heating function, with load profile indication
  4. Energy efficiency class of the water heating system
  5. Seasonal efficiency class of traditional heater
  6. Indication that the system includes a solar device
  7. Indication that the system includes a hot water tank
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