Electric Immersion Heaters/Boilers – A Comprehensive Guide

Electric immersion heaters, also known as LETsheat systems or unvented hot water systems, have long been a reliable method of heating water. Although technology has introduced more efficient alternatives, such as combi boilers, immersion heaters still serve a purpose in certain scenarios, particularly when a gas supply is unavailable. In this guide, we’ll walk you through everything you need to know about immersion heaters, from how they work to their costs, benefits, and drawbacks.

By the end, you’ll be equipped with all the information to decide whether this heating method is the right choice for your home.

What Is an Immersion Heater?

An immersion heater is essentially an electric water heater that works by immersing a heated metallic element into a water storage cylinder. As electricity flows through the element, it heats up, warming the surrounding water in the tank. Immersion heaters are often installed in homes where a gas supply is unavailable or in properties that require a backup hot water system.

The heater is connected to the main power supply and can be switched on and off as needed, giving homeowners control over when and how long the water is heated.

How Do Immersion Heaters Work?

Electric immersion heaters function similarly to a kitchen kettle. Once switched on, the electricity flows through the heating element, which in turn heats the water. Depending on the size of the cylinder and the power of the heater, it can take anywhere from 1.5 to 3 hours to heat the entire tank. The water typically needs to reach a temperature of at least 50°C to ensure that any harmful pathogens are killed.

Common Problems with Immersion Heaters

While immersion heaters were once a staple in homes across the UK, they come with several notable drawbacks that have caused many homeowners to switch to more modern heating solutions like combi boilers.

1. Slow Heating Time

One of the most significant issues with immersion heaters is the time it takes to heat the water. You cannot simply heat a small amount of water for immediate use; instead, the entire tank must be warmed, which can take hours. This not only wastes energy but also delays access to hot water.

2. High Energy Costs

Because they rely on electricity, immersion heaters are much more expensive to run than gas boilers. Without thermostatic controls, they can consume a substantial amount of electricity, especially if left on constantly.

3. Inefficiency

Once the heater is turned off, the water in the tank will gradually lose its heat, leading to energy wastage if the water is not used promptly. This makes immersion heaters an inefficient method of heating water compared to alternatives like combi boilers, which can heat water on demand.

Benefits of Immersion Heaters

Despite their drawbacks, immersion heaters offer some distinct advantages, particularly in specific situations.

1. Backup Hot Water Supply

One of the primary benefits of an immersion heater is its ability to serve as a backup water heating system. If your gas boiler breaks down, you can still use the immersion heater to get hot water, ensuring you’re not left without during an emergency.

2. Ideal for Properties Without Gas

For homes without a gas supply, such as flats or remote properties, immersion heaters offer a practical solution for hot water needs.

3. Flexible Energy Usage

With proper controls, immersion heaters can be energy-efficient. Thermostatic controls can shut off the heater once the desired temperature is reached, and timers can be set to heat water during off-peak hours, such as those on an Economy 7 tariff.

How Much Does an Immersion Heater Cost to Run?

The running cost of an immersion heater depends on its power rating and the length of time it’s in use. For example, a 6 kW immersion heater costs approximately £0.90 per hour to run, which can add up quickly over time, particularly if the heater is used daily or left on constantly.

To put this in perspective, using a 6 kW heater for 2 hours daily would cost around £1.80 per day or £12.60 per week. Some homeowners choose to leave their immersion heaters on all the time to avoid waiting for hot water, but this only increases their energy bills.

Improving Immersion Heater Efficiency

There are several ways to improve the efficiency of an immersion heater:

• Thermostatic Control: Installing a thermostat ensures the heater turns off when the water reaches the desired temperature and turns back on when it cools down.
• Insulating the Tank: An insulated tank retains heat longer, reducing the amount of energy needed to maintain water temperature.
• Timers: A timer can be set to turn the heater on during off-peak hours, saving money on electricity bills.

Immersion Heater Costs

The cost of installing an immersion heater depends on its size, type, and whether you need additional components like a storage cylinder. Here’s a breakdown of the two most common types:

1. Copper Immersion Heaters

These are the more affordable option, costing between £20 and £30. However, they are unsuitable for hard water areas or unvented systems, and they can’t be used with stainless steel tanks or thermal store units.

2. Titanium Immersion Heaters

Titanium heaters, which cost between £30 and £40, are the preferred choice for areas with hard water, as they are more durable and resistant to corrosion.

Immersion Heater Size Calculator

Choosing the right size immersion heater is crucial for efficient water heating. To determine the required power output, you need to know the volume of your water cylinder and the desired temperature increase. Use this formula to calculate the necessary power:

[ \text{Power (kW)} = \frac{\text{Volume (litres)} \times 4 \times \text{Temperature Increase (°C)}}{3412} ]

For example, if you have a 100-litre tank and want to raise the temperature by 50°C (from 10°C to 60°C), you would need a 5.8 kW heater.

Read about: No Hot Water from Your Boiler? Here’s How to Fix It

Should You Keep Your Immersion Heater On All the Time?

Contrary to popular belief, keeping your immersion heater on continuously is not cost-effective. While it may seem convenient to have hot water available at all times, the additional energy usage far outweighs the benefits. It’s much more efficient to use a heater with thermostatic controls and timers, ensuring that it only operates when necessary.

Are Immersion Heaters the Right Choice?

Immersion heaters have their place, particularly in homes without gas or as a backup heating option. However, for most homeowners, a more efficient and cost-effective alternative is a combi boiler, which provides both heating and hot water on demand.

While immersion heaters may be more expensive to run, they can be a lifesaver during a boiler breakdown or in properties where gas isn’t available. If you’re considering installing one, be sure to weigh the costs and benefits, and explore options to improve efficiency, such as thermostats, timers, and insulation.

Conclusion

LETsheat systems, or immersion heaters, continue to be a reliable source of hot water, especially in homes without access to gas. However, their higher running costs and slower heating times make them less efficient than modern alternatives like combi boilers. If you decide that an immersion heater is right for your home, consider implementing energy-saving strategies like thermostatic controls and insulation to reduce operating costs. For most households, investing in a combi boiler will provide greater efficiency, convenience, and overall savings in the long run.