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How can I produce the most cost-effective hot water?

Hot water available at all times for your convenience and pleasure: a user-pays facility. But when the choice of how to heat the water is sound, the expense can change from excessive to very affordable - and very ecological.

There are two ways of acquiring hot water: 

  • instantaneously (water heater)
  • or through storage (boiler).

Each system has its advantages and its limitations.

Water heater, flexible and fast

It can produce water ad infinitum (unlike the hot water cylinder) but at a slower flow rate. It is fine for a single tap or several very close together. It is economical to purchase and to operate (no losses as no storage) and small models are available, for a single stand-alone sink, for example.
This equipment mainly operates on gas, or electricity for top-up models. A mixed wall boiler is one option (instant domestic hot water and hot water for heating) for apartments and small houses.

Hot water cylinder, for larger quantities

The stored water (hot water cylinder) can provide showers for a family, but when the cylinder is empty you have to wait for it to fill up again. It is more cumbersome and more expensive to buy, but can be heated in a variety of ways, some of which are more economical:

  • direct electricity (preferably dual hourly rate): this is the most costly in use
  • gas: less frequent
  • connected to the boiler (gas, oil, pellets). Disadvantage: the boiler continues to run during the summer. But it becomes too large for a heat requirement of just a few showers. It will operate under poor output conditions and will wear more quickly.
  • thermal solar panels, which will supply you with 60% of your hot water consumption free and will be coupled to a boiler for top ups

Hot water cylinder + heat pump + photovoltaic = the winning combination

This latest innovation has a bright future: it is a hot water cylinder where a micro heat pump heats the water.
To achieve this, it takes free heat from the ambient air in an unheated room. For 1 kWh of paid-for electricity consumed, it recovers up to 4 kWh of free heat. And if, on top of that, the electricity is generated by photovoltaic panels, the energy consumed is free.

Ideally, this hot water cylinder should be coupled with the boiler: in summer, the boiler is switched off and the heat pump produces hot water. In winter, the heat pump is shut down and the boiler heats the water through a coil installed in the hot water cylinder. This system is still relatively inexpensive (reckon on € 2,500 excl. VAT including fitting), but it depreciates in a few years and the prices are dropping gradually.

When carrying out major renovations, why not modernise your hot water installation with the latest technologies. The Energy Managers of large apartment blocks are also following this trend with interest. Read about the experience of the Foyer Anderlechtois public housing corporation in this account .

Sami Naouar

Between 2006 and 2008, the Foyer Anderlechtois carried out a huge renovation project on a building in the area of the rue des Droits de l'Homme. During the works, the Foyer Anderlechtois paid special attention to managing the building's domestic hot water.

Read the testimonial

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