Is a Heat Pump Water Heater Cheaper To Run Than an Electric Immersion Heater?
Is a Heat Pump Water Heater Cheaper To Run Than an Electric Immersion Heater? Yes, typically a heat pump water heater is a whole lot cheaper to run than an electric immersion heater when you need to produce the same amount of hot water. Electric immersion heaters use direct electric resistance heating and give you about 1kwh of heat for every 1kwh of electricity you use on the spot. Heat pump water heaters take in extra heat from the surrounding air instead, and they typically deliver several kwh of usable heat for each kwh of electricity they use. If a heat pump operates at a coefficient of performance of 3, it will only use about one-third the amount of electricity for the same useful heat as an immersion heater would.
Why is a heat pump water heater cheaper to run?
It all comes down to how the two systems make hot water.
An electric immersion heater has an electrical heating element inside the hot water tank. Electricity goes through the element and is turned directly into heat.
A heat pump water heater uses electricity mainly to run a compressor, fan, controllers, and a refrigeration circuit. Its evaporator takes in thermal energy from the surrounding air, and the heat pump transfers that energy into the stored water.
As a result, the electricity the heat pump uses is only a small part of all the energy it delivers to the domestic hot water.
Explore our specialist product pages for more information about our heat pump water heater ranges:
Wall hung air source heat pump water heaters
Residential air source heat pump water heaters
Commercial air source heat pump water heaters
How much money could a heat pump save you compared to an immersion heater?
Let’s take a simple example where a household needs 6kwh of useful heat for the hot water.
An immersion heater would need approximately:
6kwh of electricity
If a heat pump achieved an average CoP of 3, it would theoretically need:
6 kWh ÷ 3 = 2 kWh of electricity
If electricity costs 25p per kwh, the theoretical cost would be:
SystemElectricity usedCost at 25p/kwhImmersion heater6kwh£1.50pHeat pump at CoP 23kwh£0.75pHeat pump at CoP 32kwh£0.50pHeat pump at CoP 41.5kwh£0.38p
These figures are for illustrative purposes only and don’t predict actual household running costs, but they do show why CoP has such a big impact on the cost of producing hot water.
Does a heat pump always achieve its advertised CoP?
No. A CoP is not a set efficiency figure.
Heat pump performance changes based on the conditions under which the appliance is working. Important factors include the temperature of the air entering the evaporator, the incoming cold water temperature and the required hot water temperature.
If the heat pump has to make water at 60°c from relatively cold air, its CoP will usually be lower than when it makes 50°c water from warmer air.
This means actual electricity savings should be calculated using realistic operating conditions rather than just using the highest CoP quoted on a product’s spec.
What happens if the heat pump uses its electric immersion heater?
Many heat pump water heaters have an electric immersion heater as well.
It may be used for backup, to speed up hot water recovery, for high demand or for a high-temperature legionella control cycle.
When the immersion heater is operating, it doesn’t provide the same efficiency advantage as the heat pump’s refrigeration cycle. Frequent use can therefore increase overall running costs significantly.
A correctly sized system should normally allow the heat pump to provide the majority of everyday domestic hot water heating, with the immersion heater acting primarily as a supplementary or backup heat source.
Do higher hot water temperatures increase running costs?
Generally, yes.
As you need hotter water, the compressor has to create a bigger temperature lift between the heat source and the hot water. This normally reduces CoP.
Higher cylinder temperatures can also increase standing heat losses, as there is a bigger temperature difference between the stored water and its surroundings.
For this reason, constantly running at the maximum temperature available is not the most economical approach.
What else affects the cost of heating hot water?
Running costs are influenced by more than just the CoP.
Hot water cylinder capacity, household water usage, insulation, standing heat loss, electricity tariff, operating schedule and immersion heater usage all contribute to annual electricity consumption.
Solar PV can also work particularly well with a heat pump water heater. Where surplus solar electricity is available during the day, the system can potentially schedule some of its water heating to coincide with that generation.
Is a heat pump water heater worth replacing an immersion heater?
For homes that currently use direct electric resistance heating to produce most of their domestic hot water, a heat pump water heater can offer a significant reduction in electricity consumption.
The potential saving needs to be balanced against the higher initial purchase and installation cost of the heat pump system.
However, on running costs alone, a correctly sized and properly installed heat pump water heater should normally be significantly cheaper to run than heating the same amount of water entirely with an immersion heater. The greatest savings are achieved when the heat pump provides most of the annual hot water demand and unnecessary immersion heater operation is kept to a minimum.