Can a Heat Pump Water Heater Replace Your Electric Immersion Cylinder?
Can a Heat Pump Water Heater Replace Your Electric Immersion Cylinder? Yes, heat pump water heaters can replace conventional electric immersion cylinders but use a lot less electricity to produce the same amount of hot water. An immersion heater just uses electricity to get hot and then dump it straight into the water – but an air source heat pump gets its power from the surrounding air and transfers that heat to your water. This lets a heat pump provide a whole bunch of useful heat for each unit of electricity it runs on, depending on the COP (or Coefficient of Performance) and the conditions it’s operating in.
Why Replace an Immersion Cylinder with a Heat Pump?
A traditional electric hot water cylinder is actually pretty straightforward – an electrical element just sits in the middle of the cylinder and heats up the water.
At the point of use, 1 kWh of electricity gives you 1 kWh of heat. That’s it.
Heat pump water heaters work differently though – they use their electricity to power the compressor, fan and controls, but most of the energy they use to heat the water actually comes from the air around us.
If your heat pump is operating with a COP of 3 – so it’s pretty good – then 1 kWh of electricity could give you around 3 kWh of useful heat. That can make replacing a direct electric cylinder pretty appealing if a big chunk of your annual electricity bill is used to heat your hot water.
For properties where a smaller-capacity water heater is appropriate, see our 100 litre wall hung heat pump water heating system, suitable for a range of compact domestic and light commercial installations.
For higher household demand, explore the 200 litre domestic air source water heating system or 300 litre domestic air source water heating system.
For large-scale domestic hot water requirements, see our 400 litre commercial air source water heating system or 500 litre commercial air source water heating system.
Is it a Straightforward Swap?
Not always, unfortunately. A heat pump water heater is not exactly a like-for-like swap for an immersion cylinder.
A normal electric cylinder doesn’t need any air – a heat pump does though.
An integrated heat pump water heater has all the bits like the compressor, evaporator and fan inside it, so it needs enough air to get the job done and also makes cooler air and condensate. So the place you choose to put it needs to be checked to make sure it’s got:
- Enough airflow (or is near some ducting)
- The right temperature range (minimum and maximum)
- A way to drain the condensate
- Enough space to install it
- Access for servicing and maintenance
- Not too much noise from the fan and compressor
- Hot and cold water connections
- The right electrical connections
A utility room or garage is usually a better spot than a small, cramped cupboard.
Will it Give You the Same Amount of Hot Water?
It can, provided you get the size right.
Heat pump water heaters are generally slower to heat water than an electric immersion element. Instead of relying on super-fast reheating they just store enough hot water for when you need it.
This means that getting the cylinder size and recovery time right is pretty important.
The one you choose needs to be big enough to meet the needs of you and your family, and also refill the water fast enough when you need it.
Choosing the wrong size could leave you with a cylinder that’s always needing a boost or running its immersion heater, which defeats the point of getting an energy-efficient heat pump.
Do Heat Pump Water Heaters Still Have an Immersion Heater?
Many integrated heat pump water heaters still come with an electric immersion heater.
It’s just not intended to do all the work like before – maybe it’s just for backup, rapid recovery or a special hygiene cycle.
Some newer systems – and there’s a type called a R290 heat pump water heater – can actually get the water really hot without needing to use the immersion element that often.
Having an immersion heater still comes in handy though because it gives you a backup plan in case the heat pump is out of action.
Will it Reduce Electricity Consumption?
In most cases – yes. Compared to a direct electric immersion heater, a heat pump will save you energy.
For example if you need 6 kWh of useful heat to heat the cylinder, a direct electric immersion heater would use about 6 kWh of electricity.
But a heat pump with a COP of 3 would only need about 2 kWh of electricity to give you the same 6 kWh of heat.
In real life there are loads of factors that can affect how much energy you use – temperature, the temperature of the incoming water, how hot you want the water, how much you use it, how much heat is lost from the cylinder and if you use the immersion element at all.
The key point is that a heat pump is just moving heat around rather than making it all from scratch with electricity.
Can it Work with Solar PV or Off-Peak Electricity?
And the answer is yes, in both cases it can make a heat pump water heater even more attractive.
With solar PV you can schedule the heat pump to run when you’ve got excess solar power – so you get to use that extra energy to heat your water.
With an off-peak or time-of-use electricity tariff, you can heat the cylinder when the rate is lower and then store the energy as hot water for later.
A well-insulated cylinder is basically a simple form of thermal energy storage.
Is a Heat Pump Water Heater a Good Replacement for Your Immersion Cylinder?
For a place that uses an electric immersion cylinder for all or most of its hot water, a heat pump water heater is one of the most effective ways to save on the electricity bill for water heating.
It just needs a bit more planning than just swapping one cylinder for another – airflow, condensate drainage, noise, cylinder capacity and installation space are all things you need to consider. While a dedicated air source heat pump water heater that’s properly chosen and installed will do the trick – it can deliver the same reliable hot water as an electric cylinder on a day-to-day basis – all without using nearly as much electricity to get the job done.