0
0
Posted: 22nd October 2025 | Author: Nationwide Supplies
Back to news
Immersion heaters can be a practical way to heat water - especially in homes without a gas boiler - but are they the most cost-effective option? With rising energy bills, it’s worth taking a closer look at how much they actually cost to run so you can decide whether an immersion heater is the right choice for your property or project.
Whether you're considering one for daily use or as a backup, this guide will walk you through the ins and outs of immersion heater running costs, key factors, and efficiency tips to help you make an informed decision.
Before deciding on an immersion heater, it’s important to take a step back and look at the bigger picture. Understanding how effectively an immersion heater would suit your specific needs and circumstances can help you make a well-informed choice. Here are some of the most important pros and cons.
One of the advantages of an immersion heater is that it heats water directly within the storage cylinder. This reduces the heat lost through pipework that can occur with centralised heating systems, especially in older homes. Less heat loss means getting more out of your energy bill - a win for efficiency.
If your hot water needs are minimal or confined to certain times of day, this direct heating method can offer practical benefits. However, overall cost savings still depend heavily on usage patterns and how well your system retains heat once it's warmed.
Immersion heaters are powered by electricity, which generally costs more per kilowatt-hour than gas. This means that if you’re relying on your immersion heater to supply all your hot water on a daily basis, it can quickly become expensive.
For example, running a 3kW immersion heater for an hour could cost around £0.75 based on current average energy prices - and that adds up if used regularly. So, for everyday use, immersion heaters may not be the most budget-friendly option.
How well your hot water cylinder is insulated plays a big role in how efficient your immersion heater is. A properly insulated tank retains heat for longer, meaning the heater doesn’t need to kick in as often to maintain temperature. Lagging jackets or integrated foam insulation help keep heat loss to a minimum, especially overnight or during off-peak usage.
If your immersion heater is struggling to keep water warm or you find yourself reheating more than expected, poor insulation may be to blame. Upgrading your insulation is a simple and affordable way to reduce overall running costs and get more value from your setup without the need for a full overhaul.
An integrated thermostat means your immersion heater will cut out once the water has reached the desired temperature, meaning you’re not wasting money heating your water more than needed.
Basic or outdated heaters may lack this feature and use up unnecessary energy, especially if the heater is left on for long periods without supervision. Modern units with built-in thermostats or connected to external timers offer much better control, preventing overheating and helping cut down on electricity consumption.
If you're using an older immersion heater, it’s worth checking whether an upgrade or a plug-in timer could help you manage running times more effectively. Left unchecked, inefficient operation is a key reason why immersion heaters earn a reputation for being costly to run.
If you only need hot water occasionally - for example, in a holiday let, second home or as a backup for a gas boiler - immersion heaters can be a very sensible choice. They’re easy to install, require minimal maintenance and heat water on demand when switched on.
In this context, the higher running cost per use becomes less of a concern because you're not relying on it as your main hot water source. If you need an immersion heater for everyday use, it might not be as cost-efficient - but it’s still worth weighing it up as an option against other water heating methods to see how an immersion heater might work for you.
Top tip! Consider whether you could save money by using your immersion heater at off peak times or during cheaper periods on a time-of-use tariff.
You may have heard people advise leaving heating systems on 24/7 during cold seasons to maintain a steady temperature in the home and keep costs down since the system doesn’t have to heat up from scratch each time. But is this the right way to go with an immersion heater?
The short answer is no. Leaving an immersion heater on constantly isn’t usually the most efficient way to heat your water. Even with a thermostat to regulate temperature, the heater will still use energy to maintain heat throughout the day - even when you’re not using hot water. Over time, this can lead to higher-than-necessary energy bills.
For example, a standard 3kW immersion heater running for three hours a day costs around £2.43 daily (based on an average electricity rate of £0.27 per kWh). That’s roughly £68 per month (calculated as 28 days here).
Now, if you leave your immersion heater on all day, that doesn’t mean it’ll be working at full power all that time, so it’s not quite as simple as increasing the usage up to 24 hours per day. But if we say for example that your immersion heater runs for six hours instead of three, that doubles your energy costs to £4.86 per day and £136 per month - just for your immersion heater!
Want to understand how your personal energy costs would be affected? To find the kWh, multiply the kW rating of your heater by the time in hours you expect to use it. Then times the resulting number by your unit rate for electricity.
A better approach is to run the immersion heater only when needed. Using a timer or manual switch helps match heating times to your household’s routine and cuts down on waste without having to compromise on comfort.
Immersion heaters aren’t the best choice for everyone, but they can be an excellent addition to your property in the right circumstances. By understanding how they work and how to manage their usage wisely, you can decide whether an immersion heater is right for you.
Back to news
