Water heaters: choosing, installing, and maintaining

A water heater is one of the most important devices in any home. It ensures a steady supply of domestic hot water (DHW) and enhances daily comfort; when properly selected, it also contributes to energy savings. In a context where energy efficiency and sustainability are top priorities, choosing, installing, and maintaining your water heater correctly is key to optimising energy use and complying with current regulations.

Types of water heaters: which one should you choose?

The right water heater depends on several factors: the number of residents, frequency of use, available energy sources, and space limitations. The most common models today are described as follows:

Electric water heaters

Electric water heaters are an efficient solution for homes without a gas connection. They are generally divided into two main types depending on how they operate:

• Storage water heater (tank):
  It has a built-in tank that stores hot water. It’s ideal for homes with moderate consumption and stable routines, as you can programme heating cycles for specific times of day.
• Instant water heater: It heats water on demand, without prior storage. This type requires higher electrical power to operate efficiently.

Among its advantages are easy installation and no need for a venting system. Still, its energy consumption can be higher if not used efficiently.

Gas water heaters

Gas water heaters use natural gas or butane to heat water instantly. They’re especially recommended for homes with high consumption, as they provide continuous DHW without storage. Their main advantage is the low energy cost per litre of hot water, making them an efficient long-term option. However, they require a professional installation and a compliant flue system for exhaust gases.

Heat pump water heaters

This type of water heater uses aerothermal technology to capture energy from the air and transfer it to the water. It’s currently the most efficient option available for consumers, with very low energy consumption and performance far superior to conventional systems. In addition, these systems may qualify for public grants due to their contribution to energy efficiency. The main drawback is the higher upfront cost and the need for enough space to install the outdoor unit.

Solar thermal water heaters

Solar thermal heaters use solar radiation as their main energy source to heat water, making them a sustainable and low-impact alternative. They are typically installed on the roof of a building or home and are often combined with backup systems such as heating elements or boilers to ensure supply on cloudy days or during high demand.

Their main advantage is that they harness a free and renewable energy source. However, they require proper orientation to maximise solar gain, along with regular maintenance to ensure optimal performance.

Installation: technical and regulatory requirements

The installation of any type of water heater must follow specific technical standards to ensure safety, proper operation, and legal compliance. This includes proper equipment placement, safe hydraulic and electrical connections, and the involvement of licensed professionals to certify compliance with current regulations.

Proper location for a water heater

Choosing the right location is essential for safety and performance. Gas models must be installed in well-ventilated areas and have an approved flue system to safely expel combustion gases. Electric water heaters can be placed indoors, provided they’re kept away from heat sources and protected from humidity to avoid electrical hazards.

Legal and technical requirements for water heater installation

Installing a water heater —especially a gas one— must meet several regulatory requirements to ensure safety and proper performance. It is mandatory to register the equipment with the relevant regional authority, certifying that the installation meets the required technical standards. You must also have an installation certificate and commissioning report issued by a qualified professional.

Regardless of the type of heater, the work must be performed by a certified technician. The installation should include protection elements such as a pressure relief valve, pressure group, and backflow prevention system to avoid issues in the water network. For electric models, it’s recommended to connect them to a dedicated line with residual current protection to improve safety and prevent interference with other household devices.

Maintenance: how to extend the lifespan of a water heater

Proper maintenance not only improves energy efficiency but also reduces the risk of breakdowns and extends the life of the unit. Below are the main maintenance actions to keep your system in optimal condition:

Regular inspection

Gas water heaters should be inspected every two years by an authorised technician to check components, combustion quality, and gas exhaust. For electric models, it’s recommended to have the resistance and magnesium anode inspected yearly. The anode is essential to prevent internal corrosion in the tank.

Cleaning and descaling

In areas with hard water (high mineral content), lime buildup can severely affect heater performance. It’s recommended to descale the system every 12 to 18 months. This process helps maintain efficiency and prevents unnecessary energy consumption.

Pressure and temperature control

Maintaining water pressure between 1 and 3 bars is crucial for optimal operation. Adjusting the thermostat to a temperature between 45 °C and 55 °C optimises consumption, prevents overheating, and prolongs the heater’s lifespan while improving safety.

Component replacement

Certain parts must be replaced periodically. The magnesium anode should be changed every 2–3 years to protect against corrosion. It’s also important to check and replace seals, valves, and electrical components when worn to ensure safe, efficient operation.

When should you replace your water heater?

Although most water heaters last over 10 years, some signs indicate it’s time for a replacement: If water takes longer to heat, doesn’t reach the desired temperature, leaks or drips are frequent, or your energy consumption rises unexpectedly, your unit may be losing efficiency. You should also verify compliance with current safety and efficiency regulations. Upgrading to a newer model can result in significant energy savings and greater comfort at home.

Energy efficiency grants and deductions

In 2025, the installation of efficient water heaters may qualify for several public programmes that promote energy savings:

• Personal Income Tax deduction (IRPF): Up to 40% of the cost can be deducted if the improvement enhances your home’s energy rating.
• Regional subsidies: Many autonomous communities offer incentives for systems using heat pumps or solar thermal energy.
• National programmes: Initiatives such as PREE (Energy Rehabilitation Program for Buildings) or MOVES include eligible actions for heating and hot water systems.

To access these incentives, you must have an up-to-date energy certificate, submit a detailed bill and proof of payment, and ensure that installation was performed by an authorised company meeting technical requirements.

Comfort, efficiency, and savings: the value of making the right choice

Selecting the right water heater, installing it properly, and maintaining it well are decisions that directly affect your home’s comfort, energy consumption, and sustainability. At Endesa, we help you find the most efficient solution for your home, offering expert advice, options tailored to your needs, and access to available grants.