Immersion Heaters Explained: How They Work and Which Type to Choose

An immersion heater provides hot water by using an electrical heating element submerged directly in a hot water cylinder or tank. It can be used as a primary source of hot water in some properties or as a backup when a boiler or other heating system isn't available.

Whether you're replacing an existing element or choosing one for a new installation, understanding how immersion heaters work and the differences between copper and Incoloy elements can help you make an informed choice.

What Is an Immersion Heater?

An immersion heater is an electrical heating element fitted into a water cylinder or tank. When switched on, electricity passes through the element, generating heat that transfers to the surrounding water.

Many domestic immersion heaters are installed in hot water cylinders and include a thermostat to regulate the water temperature. Depending on the installation, an immersion heater can work independently of the central heating boiler or provide an alternative way to heat stored hot water.

You can browse Plumbco's range of immersion heaters to compare available products.

How Does an Immersion Heater Work?

An immersion heater uses electrical resistance to generate heat. When the element is powered, it warms the water around it until the thermostat reaches its set temperature and switches the heating element off.

If the water temperature subsequently falls, the thermostat can switch the element back on when required.

Immersion heaters can be controlled manually or through compatible timers and heating controls. Scheduling operation around your hot water requirements may help manage electricity use, depending on your tariff, cylinder insulation and household demand.

Electrical installation, replacement and maintenance should be carried out by a suitably qualified professional.

Where Are Immersion Heaters Used?

Immersion heaters are commonly fitted to domestic hot water cylinders, including systems where water is heated by a boiler or another heat source.

They can be useful in several situations:

• Backup hot water: Providing an alternative source of hot water if the main heating system is unavailable.

• Properties without a gas boiler: Heating stored water in suitable electric hot water systems.

• Supplementary water heating: Providing additional heating flexibility where the cylinder and controls are designed for it.

• Replacement installations: Replacing a worn or faulty immersion heater with a compatible element.

The correct element depends on the cylinder design, connection size, electrical supply and manufacturer's requirements.

Copper vs Incoloy Immersion Heaters

One of the key considerations when choosing an immersion heater is the material used for the element sheath. Copper and Incoloy are two options you'll encounter when comparing products.

Neither material is automatically the best choice for every installation. Water chemistry, operating conditions and the manufacturer's recommendations should all be considered.

Copper Immersion Heaters

Copper elements are widely used in domestic hot water applications and offer good heat-transfer properties.

When considering a copper immersion heater, check the manufacturer's guidance on water quality and suitability for your cylinder. Copper may be suitable for certain installations, but its performance and service life depend on the operating environment.

Incoloy Immersion Heaters

Incoloy is a family of nickel-based alloys used in heating elements. Particular Incoloy grades can offer useful corrosion resistance and mechanical properties in demanding operating conditions.

An Incoloy immersion heater may be suitable where the manufacturer specifies it for the water chemistry and application. However, the exact alloy grade and product design matter, so don't assume every Incoloy element is suitable for every hard-water area.

Which Is Better: Copper or Incoloy?

The best choice depends on the specific installation rather than the material name alone.

Before choosing, consider:

• Water chemistry: Mineral content and other water characteristics can affect element performance and scale formation.

• Manufacturer recommendations: Check which element material is approved for your cylinder and intended use.

• Operating conditions: Consider the temperature, usage pattern and other conditions the element will experience.

• Compatibility: Confirm the element's dimensions, connection and electrical rating match the existing installation.

If you're replacing an existing element, check the cylinder manufacturer's instructions and the specifications of the original part before ordering.

How to Choose the Right Immersion Heater

Before buying a replacement or new immersion heater, check the following details.

1. Connection size and fitting

Confirm the connection type and size, along with the length and dimensions required for your cylinder. An element that doesn't fit the cylinder correctly may be unsuitable for installation.

2. Electrical rating

Check the element's voltage and power rating against the existing electrical supply and cylinder requirements. Do not assume that elements with similar dimensions have the same electrical specifications.

3. Element material

Compare copper and Incoloy options in line with the manufacturer's recommendations and the water conditions at your property.

4. Thermostat and controls

Check whether the element includes a thermostat and whether it is compatible with your existing controls. Timers and other controls must also be suitable for the installation.

5. Cylinder compatibility

Always confirm that the immersion heater is suitable for your particular cylinder, including its fitting arrangement and installation requirements.

If you're unsure which product you need, seek advice from a qualified installer before ordering.

Find Immersion Heaters at Plumbco

Plumbco stocks plumbing and heating products for trade customers and the public. Explore our range of immersion heaters to compare available elements and check their specifications.

Whether you're looking for a copper or Incoloy immersion heater, make sure the product matches your cylinder, electrical requirements and intended application.

If you need help identifying a replacement element, contact the Plumbco team with the details of your existing heater or cylinder so you can check which products may be suitable.