What are immersion heaters?

An immersion heater is an electric heating device used to heat liquids such as water or oil. It features a metal heating element, typically made from copper, stainless steel, brass or titanium, that is immersed directly into the liquid. When electricity passes through the element, it generates heat that is transferred directly into the surrounding liquid. This direct heating method makes immersion heaters a popular choice for both domestic hot water systems and industrial liquid heating applications.

This process efficiently raises the liquid’s temperature, making immersion heaters ideal for domestic heating, industrial tanks or as a backup source of hot water alongside a central heating system.

How Immersion Heaters Work

An immersion heater converts electrical energy into heat through a resistive element (often a coiled metal loop or nichrome wire). As electric current passes through the electric heating element, resistance generates heat, which is directly absorbed by the liquid.

The temperature increase is easily controlled using a built-in thermostatic control or adjustable control panel, allowing homeowners to set precise water temperatures for hot water systems, electric water heaters and oil boilers.

Key Features and Components

Construction

An immersion heater is usually cylindrical in shape and built for durability, with its heating element encased in a protective sheath to ensure safety and efficient heat transfer. Common materials include:

• Copper immersion heaters – ideal for standard hot water cylinders.
• Titanium immersion heaters – corrosion-resistant and suited to hard water areas or industrial use.

Heating Element

The electric resistance heater at the core determines the unit’s heating power. Its length and wattage affect how quickly it heats water inside a hot water cylinder or storage tank. In many homes, immersion heaters act as a secondary or backup heat source to a gas boiler, combi boiler or heat pumps. This is particularly useful when the main system is switched off or during maintenance.

Installation

Immersion heaters are fitted into a water cylinder or hot water tank via a mounting flange or threaded connection, commonly found in:

• Domestic hot water storage cylinders (vented or unvented)
• Industrial boilers and electric water heaters
• Oil tanks or chemical process containers

Homeowners on Economy 7 or off-peak electricity tariffs often schedule their immersion heater to operate overnight, taking advantage of lower electricity rates.

Temperature Control & Safety

Modern immersion heaters come equipped with thermostatic control, a pressure relief valve and an on/off switch or timer dial. These components help:

• Prevent overheating and energy waste
• Maintain consistent water temperature
• Automatically shut off once the desired temperature is reached
• They also improve energy efficiency, particularly when paired with a smart thermostat or Immersun Power Diverter for homes using solar panels or solar panel systems.

Types of Immersion Heaters

There are two main types of immersion heater, each suited to different applications:

• Submersible immersion heaters – fully submerged in the liquid, providing even heat distribution.
• Flanged immersion heaters – mounted externally on a tank or vessel, often used in industrial or commercial applications.

Common Applications

Immersion heaters are used across a wide range of domestic and industrial settings, including:

• Residential hot water systems and electric water heaters
• Used alongside combi boilers or Megaflo systems as a reliable backup source of hot water.
• Supporting oil boilers or gas boilers to provide additional hot water capacity.
• Integrated with solar water heating systems or renewable energy setups to maximise efficiency.
• Food processing, chemical and laboratory applications

They are also ideal for off-grid homes, energy-efficient properties and unvented hot water systems that rely on electric heating options instead of the gas network.

Energy Efficiency and Renewable Integration

Pairing an immersion heater with solar panels or a solar panel system allows you to use excess solar energy to heat your water, reducing reliance on fossil fuels and the gas network. This setup improves energy efficiency and lowers running costs, particularly under incentive schemes like the Smart Export Guarantee or the Renewable Heat Incentive (RHI).

Similarly, homes using a heat pump can benefit from an immersion heater as a backup water heater, ensuring a consistent supply even during colder months or maintenance periods.

If you’re on an Economy 7 or night-rate electricity plan, running your immersion heater overnight can take advantage of off-peak electricity for significant savings. This makes immersion heaters an excellent option for energy-efficient homes looking to reduce carbon output and manage costs effectively.

Safety and Maintenance

To ensure safe and efficient operation, it’s important to:

• Regularly inspect the heating element for sediment build-up or corrosion
• Ensure the thermostatic control and pressure relief valve are working correctly
• Keep your hot water cylinder insulated with an insulating jacket or foam tubing to prevent energy waste

Following the manufacturer’s guidelines and maintaining your heater can extend its lifespan and help reduce electricity consumption and running costs.

Final Thoughts

An immersion heater is a versatile, cost-effective and energy-efficient heating solution for both domestic and industrial applications. Whether it’s providing hot water as part of a central heating system, operating independently in an electric heating setup or supporting a renewable energy system, immersion heaters deliver reliable, controllable heat all year round.