What is the most efficient electric water heater?
What is the most efficient electric water heater? The most efficient electric water heater is a heat pump water heater, and you’ll see that being sold in the UK under various names, like an air source heat pump hot water cylinder or a domestic hot water heat pump.
The thing about a standard electric immersion heater, a direct unvented cylinder or an instantaneous electric water heater is that they are super efficient, at 100% efficiency at the point of use. So if you think about it, 1kW of electricity gets converted into 1kW of heat in the water.
Air-source heat pump water heaters
But an air-source heat pump domestic hot water heater works differently. Rather than just using electricity to generate all the heat, it extracts low-grade heat from the surrounding air and then turns it into usable heat for your hot water. That means it can deliver up to 2 or 4 kWs of heat for every 1 kW of electricity used, depending on the air temperature, the temperature of the water, the quality of the installation and your usage pattern. And that’s precisely what the Energy Saving Trust says about heat pumps – they’re a low-carbon heating option that takes heat from the air and can provide hot water as well as heating (Source: Energy Saving Trust)
So to answer the question “Which electric water heater uses the least electricity?”, it’s pretty clear that the answer is a heat pump water heater. However, the water heating system will be an electric storage heater system; due to how heat pumps operate, they are not available as an instantaneous version. Thus, the question is, ‘What is the most efficient electric storage heater?’ The answer is also an air-source heat pump domestic hot water heater.
Instantaneous electric water heater options
But of course the best option for you is going to depend on your specific situation. For example, with a small hand wash basin, a compact instantaneous electric water heater may be more sensible because there’s just not much water stored and you don’t lose much heat. But if you’re looking at installing something for a house, flat, office, changing rooms, a salon, or a commercial hot water system with regular demand, a heat pump cylinder will almost certainly be the most energy-efficient electric option.
Direct electric cylinders
A well-insulated direct electric unvented cylinder is nice and simple, reliable and relatively cheap to put in, but it will generally cost more to run than a heat pump cylinder. And if you’ve also got solar PV and an immersion diverter, that can certainly cut the running costs down a bit, but it’s more about changing the energy source rather than making the heater itself more efficient.
In UK market terms, typically the most efficient electric water heater is going to be an air source heat pump water heater, but the actual product that will be most suitable for you is going to depend on your hot water needs, how much space you have, the temperature of the water coming in, the condition of your electrical supply and your budget.
